Crater Isabella, with a diameter of 175 kilometers (108 miles), seen in this Magellan radar image, is the second largest impact crater on Venus. The feature is named in honor of the 15th Century queen of Spain, Isabella of Castile. Located at 30 degrees south latitude, 204 degrees east longitude, the crater has two extensive flow-like structures extending to the south and to the southeast. The end of the southern flow partially surrounds a pre-existing 40 kilometer (25 mile) circular volcanic shield. The southeastern flow shows a complex pattern of channels and flow lobes, and is overlain at its southeastern tip by deposits from a later 20 kilometer (12 mile) diameter impact crater, Cohn (for Carola Cohn, Australian artist, 1892-1964). The extensive flows, unique to Venusian impact craters, are a continuing subject of study for a number of planetary scientists. It is thought that the flows may consist of 'impact melt,' rock melted by the intense heat released in the impact explosion. An alternate hypothesis invokes 'debris flows,' which may consist of clouds of hot gases and both melted and solid rock fragments that race across the landscape during the impact event. That type of emplacement process is similar to that which occurs in violent eruptions on Earth, such as the 1991 Mount Pinatubo eruption in the Philippines.

Voir l'image PIA00480: Venus - Impact Crater 'Isabella sur le site de la NASA.

PIA00487: Venus - Volcanic Domes on Flank of Volcanic Maat in East Ovda Region

This Magellan image is centered about 3.2 degrees north latitude, 194.9 degrees longitude in the eastern Ovda region of Venus. The image, which is 90 km (56 miles) in width and 80 km (50 miles) in length, shows some small volcanic domes on the flank of the volcano Maat. The bright flows to the east are most likely rough lava flows while the darker flows to the west are probably smoother flows. The dark flows do show some roughness, however, as can be seen by the structure in the flows to the southwest. These dark flows also have some debris that has been deposited on top of the flows. The debris may be fine material from the surrounding plains on top of the flow by wind or it may be ash from the volcano. Small volcanic domes are very common features on the surface of Venus, indicating that there has been much volcanic activity on the surface. Assuming that the central volcanic cone is symmetrical in shape and knowing the length of the cone's side and the incidence angle, radar foreshortening yields a height and slope of 688 meters and 8.2 degrees, respectively for the cone. These values are similar to heights and slopes of some volcanic cones on the Earth.

Voir l'image PIA00487: Venus - Volcanic Domes on Flank of Volcanic Maat in East Ovda Region sur le site de la NASA.

PIA00463: Venus - Barton Crater

During orbits 404 through 414 on 19-20 September 1990, Magellan imaged a peak-ring crater that is 50 kilometers in diameter located at latitude 27.4 degrees north and longitude 337.5 degrees east. The name Barton has been proposed by the Magellan Science Team for this crater, after Clara Barton, founder of the Red Cross; however, the name is tentative pending approval by the International Astronomical Union.

Barton is just at the diameter size that Venus craters appear to begin to possess peak-rings instead of a single central peak or central peak complex like does 75 percent of the craters with diameters between 50 and about 15 kilometers. The floor of the crater is flat and radar-dark, indicating possible infilling by volcanic deposits sometime following the impact event. Barton's central peak ring is discontinuous and appears to have been disrupted or separated during or following the cratering process. The extremely blocky crater deposits (ejecta) surrounding Barton appear to be most extensive on the southwest to southeast (lower left to right) side of the crater.

Voir l'image PIA00463: Venus - Barton Crater sur le site de la NASA.

PIA00236: Venus - Crater Golubkina

This Magellan image mosaic shows the impact crater Golubkina, first identified in Soviet Venera 15/16 data. The crater is named after Anna Golubkina (1864-1927), a Soviet sculptor. The crater is about 34 kilometers (20.4 miles) across, similar to the size of the West Clearwater impact structure in Canada. The crater Golubkina is located at about 60.5 degrees north latitude, 286.7 degrees east longitude. Magellan data reveal that Golubkina has many characteristics typical of craters formed by a meteorite impact including terraced inner walls, a central peak, and radar bright rough ejecta surrounding the crater. The extreme darkness of the crater floor indicates a smooth surface, perhaps formed by the pounding of lava flows in the crater floor as seen in many lunar impact craters. The radar bright ejecta surrounding the crater indicates a relatively fresh or young crater. Craters with central peaks in the Soviet data range in size from about 10.60 km (6.36 miles) across. The largest crater identified in the Soviet Venera data is 140 km (84 miles) in diameter. This Magellan image strip is approximately 20 km (12 miles) wide and this piece of the image is approximately 100 km (62 miles) long. The image is a mosaic of two orbits obtained in the first Magellan radar test and played back to Earth to the Deep Space Network stations near Goldstone, Calif. and Canberra, Australia, respectively. The resolution of this image is approximately 120 meters (400 feet). The see-saw margins result from the offset of individual radar frames obtained along the orbit. The spacecraft moved from the north (top) to the south, looking to the left.

Voir l'image PIA00236: Venus - Crater Golubkina sur le site de la NASA.

PIA00464: Venus - Magellan Data Superimposed on Pioneer Venus Data - Devana Chasma and Phoebe Regio

This image covers part of the 150 kilometer (90 mile) wide, 1 to 1.5 kilometer (0.6 to 0.9 mile) deep valley, Devana Chasma. The image is a composite of the first two orbits recorded by the Magellan spacecraft in August 1990 superimposed on Pioneer Venus topography. This image is located at the intersection of Devana Chasma and the Phoebe Regio upland. It covers a region approximately 525 by 525 kilometers (315 by 315 miles), centered 288 degrees east longitude on the equator. Devana Chasma consists of radar bright lineaments, interpreted to be fault scarps, oriented in a north-northeast direction. This part of the planet is thought to be an area where the crust is being stretched and pulled apart producing a rift valley, similar to the East African rift.

Voir l'image PIA00464: Venus - Magellan Data Superimposed on Pioneer Venus Data - Devana Chasma and Phoebe Regio sur le site de la NASA.

PIA00238: Venus - Impact Crater in Guinevere Planitia

This is a Magellan image mosaic of an impact crater located in Guinevere Planitia on Venus with a rim diameter of 12.5 kilometers (7.8 miles). The area mosaiced is located at 6 degrees north latitude, 335 degrees east longitude and is from orbits 376 and 377 obtained on Sept. 15, 1990. The image is of an area about 37 km (23 miles) wide and 80 km (48 miles) long. Material thrown out from the impact forms a bright ejecta blanket surrounding most of the crater. The object that formed this crater was probably moving toward the north (top of the picture) at a shallow angle to the surface when it hit. The two lines of evidence that support this view are the "missing ejecta" on the south and the small secondary craters seen to the north. The secondary craters are formed by large blocks thrown out of the primary crater. Most of the larger blocks landed close to the crater rim, while finer material traveled farther, creating a radial pattern. The inside of the crater shows terracing caused by slumping of the inner wall. A complex central peak is also seen; it was formed by uplift of the ground when it rebounded following impact. Resolution of the Magellan data is about 120 meters (400 feet).

Voir l'image PIA00238: Venus - Impact Crater in Guinevere Planitia sur le site de la NASA.

PIA00244: Venus - Volcanic Domes East of Beta Regio

Two unusual volcanic domes are shown in this Magellan full-resolution mosaic. The image covers an area 180 by 240 kilometers (120 by 160 miles) centered at 18 degrees north latitude, 303.5 degrees east longitude, just east of Beta Regio. The dome in the south center of the image is about 45 kilometers (30 miles) across, with a 20 kilometer (13 mile) caldera, or volcanic collapse crater, in the center. The dome in the northwest corner of the image is about 30 kilometers (20 miles) across with a small (5 kilometer or 3 mile) summit crater. The very bright radar return from the western flank of this dome indicates that it has steep slopes. The flanks of the volcanoes display prominent gullies which may have been formed by slumping of surface material or thermal erosion by lava flows. Variations in the brightness with the surrounding plains show the extent of lava flows which originated at these volcanoes. Curved or bowed fractures surrounding the southern structure indicate that there has been subsidence, or sinking, of the dome following eruptive activity.

Voir l'image PIA00244: Venus - Volcanic Domes East of Beta Regio sur le site de la NASA.

PIA00243: Venus - Volcano in Parga Chasma

This comet-like tail, trending northeast from the volcanic structure, is a relatively radar-bright deposit. The volcano, with a base diameter of 5 kilometers (about 3 miles) is a local topographic high point that has slowed down northeast trending winds enough to cause deposition of this material. The streak is 35 kilometers (about 22 miles) long and 10 kilometers (about 6 miles) wide. The volcano is located at the western end of Parga Chasma at 9.4 degrees south latitude and 247.5 degrees east longitude.

Voir l'image PIA00243: Venus - Volcano in Parga Chasma sur le site de la NASA.

PIA00475: Venus - Crater 'Stefania' in N. Sedna Planitia

Crater Stephania is located at 51.3 degrees latitude, 333.3 degrees longitude in northern Sedna Planitia on Venus. With a diameter of 11 kilometers (6.8 miles) it is one of the smaller craters on Venus. Because many small meteoroids disintegrate during their passage through the dense atmosphere, there is an absence of craters smaller than 3 kilometers (1.9 miles) in diameter, and even craters smaller than 25 kilometers (15.5 miles) are relatively scarce. The apron of ejected material suggests that the impacting body made contact with the surface from an oblique angle. Upon closer observation it is possible to delineate secondary craters, impact scars from blocks ejected from the primary crater. A feature associated with this and many other Venusian craters is a radar-dark halo. Since dark radar return signifies a smooth surface, it has been hypothesized that an intense shock wave removed or pulverized previously rough surface material or that a blanket of fine material was deposited during or after the impact.

Voir l'image PIA00475: Venus - Crater 'Stefania' in N. Sedna Planitia sur le site de la NASA.

PIA00472: Venus - Impact Crater 'Jeanne

This Magellan full-resolution image shows Jeanne crater, a 19.5 kilometer (12 mile) diameter impact crater. Jeanne crater is located at 40.0 degrees north latitude and 331.4 degrees longitude. The distinctive triangular shape of the ejecta indicates that the impacting body probably hit obliquely, traveling from southwest to northeast. The crater is surrounded by dark material of two types. The dark area on the southwest side of the crater is covered by smooth (radar-dark) lava flows which have a strongly digitate contact with surrounding brighter flows. The very dark area on the northeast side of the crater is probably covered by smooth material such as fine-grained sediment. This dark halo is asymmetric, mimicking the asymmetric shape of the ejecta blanket. The dark halo may have been caused by an atmospheric shock or pressure wave produced by the incoming body. Jeanne crater also displays several outflow lobes on the northwest side. These flow-like features may have formed by fine-grained ejecta transported by a hot, turbulent flow created by the arrival of the impacting object. Alternatively, they may have formed by flow of impact melt.

Voir l'image PIA00472: Venus - Impact Crater 'Jeanne sur le site de la NASA.

PIA00269: Venus - Stereo Image Pair of Crater Goeppert-Mayer

During the third global cycle of Magellan's radar mapping mission, images were obtained at viewing angles that were slightly different than those used in the first two cycles. This strategy was designed to produce stereo image pairs, which take advantage of distortions induced by the different views to provide details of the surface topography. This is a stereo image pair of crater Goeppert-Mayer, named for the 20th Century Polish physicist and Nobel laureate (60 degrees north latitude, 26.5 degrees east longitude). The crater, 35 kilometers (22 miles) in diameter, lies above an escarpment at the edge of a ridge belt in southern Ishtar Terra. West of the crater the scarp has more than one kilometer (0.6 mile) of relief. Perception of relief may be obtained with stereo glasses or a stereoscope. Some individuals may be able to fuse the images without the aid of those devices. The radar illumination for both images is from the west, or left side of the scene. Incidence angles are: (Cycle 1 (left) 28 degrees, Cycle 3 (right) 15 degrees from vertical. Analysis of stereo image pairs allows planetary scientists to resolve details of topographic relationships on Venusian craters, volcanoes, mountain belts and fault zones. The spatial resolution of this topographic information is approximately ten times better than that obtained by Magellan's altimetry experiment.

Voir l'image PIA00269: Venus - Stereo Image Pair of Crater Goeppert-Mayer sur le site de la NASA.

PIA00215: Venus - Alpha Regio

The eastern edge of Alpha Regio is shown in this image centered at 30 degrees south latitude and 11.8 degrees east longitude (longitude on Venus is measured from 0 degrees to 360 degrees east). Seven circular, dome-like hills, averaging 25 kilometers (15 miles) in diameter with maximum heights of 750 meters (2,475 feet) dominate the scene. These features are interpreted as very thick lava flows that came from an opening on the relatively level ground, which allowed the lava to flow in an even pattern outward from the opening. The complex fractures on top of the domes suggest that if the domes were created by lava flows, a cooled outer layer formed and then further lava flowing in the interior stretched the surface. The domes may be similar to volcanic domes on Earth. Another interpretation is that the domes are the result of molten rock or magma in the interior that pushed the surface layer upward. The near-surface magma then withdrew to deeper levels, causing the collapse and fracturing of the dome surface. The bright margins possibly indicate the presence of rock debris on the slopes of the domes. Some of the fractures on the plains cut through the domes, while others appear to be covered by the domes. This indicates that active processes pre date and post date the dome-like hills. The prominent black area in the northeast corner of the image is a data gap. North is at the top of the image.

Voir l'image PIA00215: Venus - Alpha Regio sur le site de la NASA.

PIA00212: Venus Phoebe Regio

This Magellan radar image is of part of the Phoebe region of Venus. It is a mosaic of parts of revolutions 146 and 147 acquired in the first radar test on Aug. 16, 1990. The area in the image is located at 291 degrees east longitude, 20 degrees south latitude. The image shows an area 30 kilometers (19.6 miles) wide and 76 km (47 miles) long. The image shows a broad, up to 17 km (11 miles) wide, radar bright, lobate lava flow that extends 25 km (15.5 miles) northwest across the image strip. The volcanic flow appears bright in this image because it is rough on a scale of a few centimeters to a few meters (a few inches to a few yards), much like lava flows on Earth that are called by geologists "aa" (ah-ah), a Hawaiian word that probably mimics the sound the ancients uttered while running barefoot over the rough, jagged surface. It is located near the southeast flank of Phoebe Regio and has flowed into local topographic lows. This lava flow has flooded the darker plains and appears to have buried north-south trending lineaments that cut the darker material. No obvious volcanic sources area visible in this image. The flow has a markedly uniform surface texture in contrast to the more mottled texture of adjacent deposits; this suggests it may represent the most recent in a series of eruptions that subsequently have been obscured. To the north and south are northwest trending graben crustal depression, or fault, areas that may belong to the system of fractures associated with Phoebe Regio.

Voir l'image PIA00212: Venus Phoebe Regio sur le site de la NASA.

PIA00082: Venus - Lakshmi Region

This Magellan image is centered at 55 degrees north latitude, 348.5 degrees longitude, in the eastern Lakshmi region of Venus. This image, which is of an area 300 kilometers (180 miles) in width and 230 kilometers (138 miles) in length, is a mosaic of orbits 458 through 484. The image shows a relatively flat plains region composed of many lava flows. The dark flows mostly likely represent smooth lava flows similar to 'pahoehoe' flows on Earth while the brighter lava flows are rougher flows similar to 'aa' flows on Earth. (The terms 'pahoehoe' and 'aa' refer to textures of lava with pahoehoe a smooth or ropey surface, and aa a rough, clinkery texture). The rougher flows are brighter because the rough surface returns more energy to the radar than the smooth flows. Situated on top of the lava flows are three dark splotches. Because of the thick Venusian atmosphere, the small impactors break up before they reached the surface. Only the fragments from the broken up impactor are deposited on the surface and these fragments produce the dark splotches in this image. The splotch at the far right (east) has a crater centered in it, indicating that the impactor was not completely destroyed during its journey through the atmosphere. The dark splotches in the center and to the far left in this image each represent an impactor that was broken up into small fragments that did not penetrate the surface to produce a crater. The dark splotch at the left has been modified by the wind. A southwest northeast wind flow has moved some of the debris making up the splotch to the northeast where it has piled up against some small ridges.

Voir l'image PIA00082: Venus - Lakshmi Region sur le site de la NASA.

PIA00260: Venus - Comparison of Left and Right Looking Views of Imdr Region

As the Magellan mission has progressed, areas of Venus have become accessible to the imaging radar system for a second look. During Magellan's second 243-day global mapping cycle, the spacecraft was rotated 180 degrees to view the surface from the opposite direction. This pair of mosaics show a region of Venus 575 kilometers (356 miles) by 460 kilometers (285 miles) as viewed in March, 1991 from the left or west (top image) and in November, 1991 from the right or east (bottom image). The image is centered at approximately 48 degrees south latitude, 230 degrees east longitude in the Imdr region of Venus. The incidence angle of the radar beam with the surface for both observations was approximately 25 degrees from vertical. The dark band near the right edge of the March image is due to a missing segment of data from one orbit. Much of the surface appears different in the two observations. Some of the darkest areas in the top image appear patchy and bright in the bottom image. In addition, east-west trending, alternating bright and dark bands in the lower left part of the bottom image are nearly or completely invisible in the top image. Magellan scientists are currently evaluating these apparent differences to understand their origin. Two theories have been developed. In one interpretation, the right patches in the November (bottom) image are reflections from facets of surface material that are oriented toward the east with a slope of approximately 25 degrees. This would lead to strong mirror-type reflections that are only visible from the east, the direction from which the surface was viewed in November. Under the second interpretation, the surface itself is proposed to have changed between the image acquisitions. It is suggested that materials on the surface had been rearranged sometime during the 8-month period, possibly by near-surface winds. Under this interpretation, the apparent brightening of the surface is explained as a result of the removal of loose material such as dust or sand, exposing a rougher, rockier surface that would appear brighter in a radar image. Magellan scientists hope to obtain a third view of this area in July, 1992, under a viewing geometry similar to the earlier data. This should provide the information necessary to distinguish between the "viewing direction" and "surface change" interpretations.

Voir l'image PIA00260: Venus - Comparison of Left and Right Looking Views of Imdr Region sur le site de la NASA.

PIA00267: Venus - Cycle 1, 2, and 3 Images of Imdr Region

This set of three Magellan images shows a small volcano, lava plains distorted into 'wrinkle ridges', and some unusual wispy-appearing surface deposits. The images were acquired during the first, second and third mapping cycles of the mission, in March 1991, November 1991 and July 1992, respectively. The area shown is about 400 kilometers by 100 kilometers (248 by 62 miles) and is centered near 47.5 degrees south latitude, 226 degrees east longitude, in the Imdr region of Venus. The middle image, from the second cycle, was acquired with the spacecraft facing toward the west (left), while the other images were acquired with an identical east-looking geometry. The differing appearance of the second image has intrigued Magellan scientists, because of the possibility that the bright patches observed in cycle 2 may have been caused by rearrangement of loose soil material between March and November, 1991. However, by duplicating the cycle 1 viewing geometry in cycle 3, the surface change theory has been tentatively ruled out. Instead, the radar brightness variations are attributed to reflections from an undulating surface, such as sand ripples or small dunes, that have an asymmetry in the east-west direction. The deposits are apparently associated with a 78 kilometers (48 miles) diameter impact crater, Stowe, which lies about 500 kilometers (310 miles) to the northeast. The fine-grained material created during the impact event may have settled out to form the unusual surface deposits observed here. Scientists are now trying to determine if the proposed ripple structures formed at the time of the impact, or are the result of ongoing wind action at the surface. Data quality during portions of cycle 3 was adversely affected by a faulty transmitter aboard the spacecraft, leading to the missing strips in the bottom image.

Voir l'image PIA00267: Venus - Cycle 1, 2, and 3 Images of Imdr Region sur le site de la NASA.

PIA00085: Venus - Lineated Plains in Lakshmi Region

This mosaic shows an area of the Lakshmi region that is located 30 degrees north latitude and 333.3 degrees east longitude. (Longitude on Venus is measured from 0 degrees to 360 degrees east). The area shown measures about 37 kilometers (23 miles) wide and 80 kilometers (50 miles) long. Based on data from the Pioneer Venus Orbiter and the ground-based Arecibo Radar Observatory, it is known that this region is located on the low rise that separates Sedna Planitia and Guinevere Planitia, just to the west of Eistla Regio. Two sets of parallel lineations are seen intersecting almost at right angles. The fainter lineations are spaced at regular intervals of about one kilometer (0.6 mile) and extend beyond the boundary of the image. The width of the faint lineations is at the limit of resolution of the best Magellan images. The brighter, more dominant lineations are less regular and, in places, appear to begin and end where they intersect the fainter lineations. It is not clear whether the two sets of lineations are faults or fractures, but in other Magellan images, these bright lineations are associated with pit craters and volcanic features. This type of terrain has not been seen on Venus nor on other planets. North is at the top of the image.

Voir l'image PIA00085: Venus - Lineated Plains in Lakshmi Region sur le site de la NASA.

PIA00242: Venus - Ovda Regio

This Magellan image shows part of the northern boundary of Ovda Regio, one of the large highlands ringing the equator of Venus. The scene consists largely of low-relief, rounded linear ridges. These ridges, 8-15 kilometers (5-9 miles) in width and 30-60 kilometers (20-40 miles) long, lie mostly along a 100-200 kilometer (60-120 mile) wide slope where the elevation drops 3 kilometers (2 miles) from Ovda Regio to the surrounding plains. Some of the ridges have been cut at right angles by extension fractures. Dark material, either lava or windblown dirt, fills the region between the ridges. The curvilinear, banded nature of these ridges suggests that crustal shortening, roughly oriented north-south, is largely responsible for their formation. Such crustal shortening was unexpected by Magellan scientists, who believed that Ovda Region, a likely site of hot upwelling from the interior of Venus, should be dominated by volcanism and crustal extension. This image, centered approximately at 1 degree north, 81 degrees east, measures 300 kilometers (190 miles) by 225 kilometers (140 miles) and was acquired by Magellan in November 1990.

Voir l'image PIA00242: Venus - Ovda Regio sur le site de la NASA.

PIA00239: Venus - Crater Aurelia

This Magellan image shows a complex crater, 31.9 kilometers (20 miles) in diameter with a circular rim, terraced walls, and central peaks, located at 20.3 degrees north latitude and 331.8 degrees east longitude. Several unusual features are evidenced in this image: large dark surface up range from the crater; lobate flows emanating from crater ejecta, and very radar-bright ejecta and floor. Aurelia has been proposed to the International Astronomical Union, Subcommittee of Planetary Nomenclature as a candidate name. Aurelia is the mother of Julius Caesar.

Voir l'image PIA00239: Venus - Crater Aurelia sur le site de la NASA.

PIA00245: Venus - 600 Kilometer Segment of Longest Channel on Venus

This compressed resolution radar mosaic from Magellan at 49 degrees north latitude, 165 degrees east longitude with dimensions of 460 by 460 kilometers (285 by 285 miles), shows a 600 kilometers (360 mile segment of the longest channel discovered on Venus to date. The channel is approximately 1.8 kilometers (1.1 miles) wide. At more than 7,000 kilometers (4,200 miles) long, it is several hundred kilometers longer than the Nile River, Earth's longest river, thus making it the longest known channel in the solar system. Both ends of the channel are obscured, however, so its original length is unknown. The channel was initially discovered by the Soviet Venera 15-16 orbiters which, in spite of their one kilometer resolution, detected more than 1,000 kilometers (620 miles) of the channel. These channel-like features are common on the plains of Venus. In some places they appear to have been formed by lava which may have melted or thermally eroded a path over the plains' surface. Most are 1 to 3 kilometers (0.6 to 2 miles) wide. They resemble terrestrial meandering rivers in some aspects, with meanders, cutoff bows and abandoned channel segments. However, Venus channels are not as tightly sinuous as terrestrial rivers. Most are partly buried by younger lava plains, making their sources difficult to identify. A few have vast radar-dark plains units associated with them, suggesting large flow volumes. These channels, with large deposits appear to be older than other channel types, as they are crossed by fractures and wrinkle ridges, and are often buried by other volcanic materials. In addition, they appear to run both upslope and downslope, suggesting that the plains were warped by regional tectonism after channel formation. Resolution of the Magellan data is about 120 meters (400 feet).

Voir l'image PIA00245: Venus - 600 Kilometer Segment of Longest Channel on Venus sur le site de la NASA.

PIA00237: Venus - Asteria Regio and Phoebe Regio

This view of the surface of Venus acquired by the Magellan spacecraft shows a geographically young region of lowland plains. The location is near the equator between two highland areas known as Asteria Regio and Phoebe Regio. Illumination in the radar image is from the left (west); in this transformed version the viewer looks due north with a slant angle of about 10 degrees. The region seen is about 40 kilometers (24 miles) wide and stretches 600 km (360 miles) down range to the north. Complex canyon systems that trend northeast and northwest were produced as Venus' crust was pulled apart by extensional forces. Some were filled with younger lava flows. The canyons are typically 5 to 10 km (3 to 6 miles) wide, 50 to 100 km (30 to 60 miles) long and rimmed by fault scarps a hundred meters or so high.

Voir l'image PIA00237: Venus - Asteria Regio and Phoebe Regio sur le site de la NASA.

PIA00465: Venus - Comparison of Venera and Magellan Resolutions

These radar images show an identical area on Venus (centered at 110 degrees longitude and 64 degrees north latitude) as imaged by the U.S. Magellan spacecraft in 1991 (left) and the U.S.S.R. Venera 15/16 spacecraft in the early 1980's (right). Illumination is from the left (or west) in the Magellan image (left) and from the right (or east) in the Venera image (right). Differences in apparent shading in the images are due to differences in the two radar imaging systems. Prior to Magellan, the Venera 15/16 data was the best available for scientists studying Venus. Much greater detail is visible in the Magellan image owing to the greater resolution of the Magellan radar system. In the area seen here, approximately 200 small volcanoes, ranging in diameter from 2 to 12 kilometers (1.2 to 7.4 miles) can be identified. These volcanoes were first identified as small hills in Venera 15/16 images and were predicted to be shield-type volcanoes constructed mainly from eruptions of fluid lava flows similar to those that produce the Hawaiian Islands and sea floor volcanoes - a prediction that was confirmed by Magellan. These small shield-type volcanoes are the most abundant geologic feature on the surface of Venus, believed to number in the hundreds of thousands, perhaps millions, and are important evidence in understanding the geologic evolution of the planet. The only other planet in our Solar System with this large number of volcanoes is Earth. Clearly visible in the Magellan image are details of volcano morphology, such as variation in slope, the occurrence and size range of summit craters, and geologic age relationships between adjacent volcanoes, as well as additional volcanoes that were not identifiable in the Venera image.

Voir l'image PIA00465: Venus - Comparison of Venera and Magellan Resolutions sur le site de la NASA.

PIA00462: Venus - Multiple-Floored, Irregular Impact Crater

Magellan imaged this multiple-floored, irregular impact crater at latitude 16.4 degrees north, longitude 352.1 degrees east, during orbits 481 and 482 on 27 September 1990. This crater, about 9.2 kilometers in maximum diameter, was formed on what appears to be a slightly fractured, radar-dark (smooth) plain. The abundant, low viscosity flows associated with this cratering event have, however, filled local, fault-controlled troughs (called graben). These shallow graben are well portrayed on this Magellan image but would be unrecognizable but for their coincidental infilling by the radar-bright crater flows. This fortuitous enhancement by the crater flows of fault structures that are below the resolution of the Magellan synthetic aperture radar is providing the Magellan Science Team with valuable geologic information. The flow deposits from the craters are thought to consist primarily of shock melted rock and fragmented debris resulting from the nearly simultaneous impacts of two projectile fragments into the hot (800 degrees Fahrenheit) surface rocks of Venus. The presence of the various floors of this irregular crater is interpreted to be the result of crushing, fragmentation, and eventual aerodynamic dispersion of a single entry projectile during passage through the dense Venusian atmosphere.

Voir l'image PIA00462: Venus - Multiple-Floored, Irregular Impact Crater sur le site de la NASA.

PIA00486: Venus - System of Lava Flows and Ridge Belt

This is a 225 meter per pixel Magellan radar image mosaic of Venus, centered at 47 degrees south latitude, 25 degrees east longitude in the Lada region. The scene is approximately 550 kilometers (341 miles) east-west by 630 kilometers (391 miles) north-south. The mosaic shows a system of east-trending radar-bright and dark lava flows encountering and breaching a north-trending ridge belt (left of center). Upon breaching the ridge belt, the lavas pool in a vast, radar-bright deposit (covering approximately 100,000 square kilometers [right side of image]). The source caldera for the lava flows, named Ammavaru, lies approximately 300 kilometers (186 miles) west of the scene.

Voir l'image PIA00486: Venus - System of Lava Flows and Ridge Belt sur le site de la NASA.

PIA00205: Venus - First Radar Test

After traveling more than 1.5 billion kilometers (948 million miles), the Magellan spacecraft was inserted into orbit around Venus on Aug. 10, 1990. This mosaic consists of adjacent pieces of two Magellan image strips obtained on Aug. 16 in the first radar test. The radar test was part of a planned In Orbit Checkout sequence designed to prepare the Magellan spacecraft and radar to begin mapping after Aug. 31. The strip on the left was returned to the Goldstone Deep Space Network station in California; the strip to the right was received at the DSN in Canberra, Australia. A third station that will be receiving Magellan data is located near Madrid, Spain. Each image strip is 20 km (12 miles) wide and 16,000 km (10,000 miles) long. This mosaic is a small portion 80 km (50 miles) long. This image is centered at 21 degrees north latitude and 286.8 degrees east longitude, southeast of a volcanic highland region called Beta Regio. The resolution of the image is about 120 meters (400 feet), 10 times better than previous images of the same area of Venus, revealing many new geologic features. The bright line trending northwest southeast across the center of the image is a fracture or fault zone cutting the volcanic plains. In the upper left corner of the image, a multiple ring circular feature of probable volcanic origin can be seen, approximately 4.27 km (2.65 miles) across. The bright and dark variations seen in the plains surrounding these features correspond to volcanic lava flows of varying ages. The volcanic lava flows in the southern half of the image have been cut by north south trending faults. This area is similar geologically to volcanic deposits seen on Earth at Hawaii and the Snake River Plains in Idaho.

Voir l'image PIA00205: Venus - First Radar Test sur le site de la NASA.

PIA00202: Venus - Aine Corona (F-MIDR 59S164)

This Magellan radar image shows a region approximately 300 kilometers (180 miles) across, centered on 59 degrees south latitude, 164 degrees east longitude and located in a vast plain to the south of Aphrodite Terra. The data for this image was obtained in January 1991. The large circular structure near the center of the image is a corona, approximately 200 kilometers (120 miles) in diameter and provisionally named Aine Corona. Just north of Aine Corona is one of the flat-topped volcanic constructs known as 'pancake' domes for their shape and flap-jack appearance. This pancake dome is about 35 kilometers (21 miles) in diameter and is thought to have formed by the eruption of an extremely viscous lava. Another pancake dome is located inside the western parts of the annulus of the corona fractures. Complex fracture patterns like the one in the upper right of the image are often observed in association with coronae and various volcanic features. They are thought to form because magma beneath the surface follows pre-existing fracture patterns. When eruptions or other movements of the magma occur, the magma drains from the fractures and the overlying surface rock collapses. Other volcanic features associated with Aine Corona include a set of small domes, each less than 10 kilometers (6 miles) across, located along the southern portion of the annulus of fractures, and a smooth, flat region in the center of the corona, probably a relatively young lava flow. The range of volcanic features associated with coronae suggests that volcanism plays a significant role in their formation.

Voir l'image PIA00202: Venus - Aine Corona (F-MIDR 59S164) sur le site de la NASA.

PIA00095: Three-dimensional perspective views of Venusian Terrains composed of reduced resolution left-looking synthetic-aperture radar images merged with altimetry data from the Magellan spacecraft.

The view shows part of Galindo (V40) quadrangle looking north; 200 km wide Nagavonyi Corona is in the foreground. Coronae are roughly circular, volcanic features believed to form over hot upwellings of magma within the Venusian mantle. A 2-km shield volcano behind the corona partly buries the Phoebo Regio highlands (shown as radar-bright mounds).

Voir l'image PIA00095: Three-dimensional perspective views of Venusian Terrains composed of reduced resolution left-looking synthetic-aperture radar images merged with altimetry data from the Magellan spacecraft. sur le site de la NASA.

PIA00084: Venus - Eistla Region

This Magellan full resolution mosaic, centered at 12.3 north latitude, 8.3 degrees east longitude, shows an area 160 kilometers (96 miles) by 250 kilometers (150 miles) in the Eistla region of Venus. The prominent circular features are volcanic domes, 65 kilometers (39 miles) in diameter with broad, flat tops less than one kilometer (0.6 mile) in height. Sometimes referred to as 'pancake' domes, they represent a unique category of volcanic extrusions on Venus formed from viscous (sticky) lava. The cracks and pits commonly found in these features result from cooling and the withdrawal of lava. A less viscous flow was emitted from the northeastern dome toward the other large dome in the southwest corner of the image.

Voir l'image PIA00084: Venus - Eistla Region sur le site de la NASA.

PIA00083: Venus - Adivar Crater

Many of the impact craters of Venus revealed by Magellan have characteristics unlike craters on any other planetary body. This 30-kilometer (18.6-mile) diameter crater, named Adivar crater for the Turkish educator and author Halide Adivar (1883-1964), is located just north of the western Aphrodite highland (9 degrees north latitude, 76 degrees east longitude). Surrounding the crater rim is ejected material which appears bright in the radar image due to the presence of rough fractured rock. A much broader area has also been affected by the impact, particularly to the west of the crater. Radar-bright materials, including a jet-like streak just west of the crater, extend for over 500 kilometers (310 miles) across the surrounding plains. A darker streak, in a horseshoe or paraboloidal shape, surrounds the bright area. Radar-dark (i.e., smooth) paraboloidal streaks were observed around craters in earlier Magellan images, but this is a rare bright crater streak. These unusual streaks, seen only on Venus, are believed to result from the interaction of crater materials (the meteoroid, ejecta, or both) and high-speed winds in the upper atmosphere. The precise mechanism that produces the streaks is poorly understood, but it is clear that the dense atmosphere of Venus plays an important role in the cratering process.

Voir l'image PIA00083: Venus - Adivar Crater sur le site de la NASA.

PIA00261: Venus - Volcanos in Guinevere Planitia

This image, with radar illumination from west to east, shows three unusual volcanoes located in the Guinevere Planitia lowland. At the center of the image is a large feature (50 kilometers or 31 miles in diameter) with an unusual shape; very round when viewed from above with steep slides and a flat top. These volcanoes are believed to be the result of relatively thick and sticky (viscous) lava flows that originated from a point source. Although a faint remnant of its original circular shape is preserved, the northern rim of this center volcano has a steep scarp. The scarp is probably the result of material that has slid away from the volcano and subsequently has been covered by lava flows. This volcano overlaps another feature to the southwest that is about 45 kilometers (28 miles) in diameter and disrupted by many fractures. The southeastern volcano (25 kilometers or 15.5 miles in diameter) appears to be the highest of the three as its illuminated western edge has the brightest radar return. The scalloped edges give this feature a bottlecap-like appearance. The highly scalloped edges are probably the result of multiple material slides along the volcano margin.

Voir l'image PIA00261: Venus - Volcanos in Guinevere Planitia sur le site de la NASA.

PIA00213: Venus - Ushas Mons

This area of Venus northeast of Ushas Mons measures 40 by 112 kilometers (25 by 70 miles) and shows evidence of possible explosive volcanism. A surface deposit that shows brightly in radar extends and broadens away from the 1 kilometer diameter (0.6 mile diameter) crater in the middle of the image. The deposit is brighter near the crater, fades gradually into the plains and ends about 10 kilometers (6 miles) from the crater. The underlying crisscross pattern becomes more visible away from the crater as the covering deposit thins out. These characteristics are typical of deposits on Earth formed by fallout from volcanic explosion plumes. A similar but darker deposit extends to the right of the crater. The crater on the western edge of the image also shows similar deposits. North is at the top of the image. The Magellan Mission Magellan is a NASA spacecraft mission to map the surface of Venus with imaging radar. The basic scientific instrument is a synthetic aperture radar, or SAR, which can look through the thick clouds perpetually shielding the surface of Venus. Magellan is in orbit around Venus which completes one turn around its axis in 243 Earth days. That period of time, one Venus day, is the length of Magellan's primary mission. During that time Magellan will map about 80 percent of the Venus surface. Subsequent missions of equal duration will provide complete mapping of the planet. Magellan was launched May 4, 1989, aboard the space shuttle Atlantis and went into orbit around Venus August 10, 1990. The spacecraft completes one orbit every three hours and 15 minutes, passing as close to the planet as 294 kilometers (183 miles) and as far away from Venus as 8,472 kilometers (5,265 miles). The smallest objects seen in this image measure approximately 120 meters (400 feet).

Voir l'image PIA00213: Venus - Ushas Mons sur le site de la NASA.

PIA00214: Venus - Lavinia Region Impact Craters

Three large meteorite impact craters, with diameters that range from 37 to 50 kilometers (23 to 31 miles), are seen in this image of the Lavinia region of Venus. The image is centered at 27 degrees south latitude and 339 degrees east longitude (longitude on Venus is measured from 0 degrees to 360 degrees east), and covers an area 550 kilometers (342 miles) wide by about 500 kilometers (311 miles) long. Situated in a region of fractured plains, the craters show many features typical of meteorite impact craters, including rough (bright) material around the rim, terraced inner walls and central peaks. Numerous domes, probably caused by volcanic activity, are seen in the southeastern corner of the mosaic. The domes range in diameter from 1 to 12 kilometers (0.6 to 7 miles). Some of the domes have central pits that are typical of some types of volcanoes. North is at the top of the image.

Voir l'image PIA00214: Venus - Lavinia Region Impact Craters sur le site de la NASA.

PIA00473: Venus - Sag Caldera 'Sachs Patera

This image of Sachs Patera on Venus is centered at 49 degrees north, 334 degrees east. Defined as a sag-caldera, Sachs is an elliptical depression 130 meters (81 feet) in depth, spanning 40 kilometers (25 miles) in width along its longest axis. The morphology implies that a chamber of molten material drained and collapsed, forming a depression surrounded by concentric scarps spaced 2-to-5 kilometers (1.2- to-3 miles) apart. The arc-shaped set of scarps, extending out to the north from the prominent ellipse, is evidence for a separate episode of withdrawal; the small lobe-shaped extension to the southwest may represent an additional event. Solidified lava flows 10-to-25 kilometers (6-to-16 miles) long, give the caldera its flower-like appearance. The flows are a lighter tone of gray in the radar data because the lava is blockier in texture and consequently returns more radar waves. Much of the lava, which was evacuated from the chamber, probably traveled to other locations underground, while some of it may have surfaced further south. This is unlike calderas on Earth, where a rim of lava builds up in the immediate vicinity of the caldera.

Voir l'image PIA00473: Venus - Sag Caldera 'Sachs Patera sur le site de la NASA.

PIA00474: Venus - Impact Crater in Eastern Navka Region

This Magellan image, which is 50 kilometers (31 miles) in width and 80 kilometers (50 miles) in length, is centered at 11.9 degrees latitude, 352 degrees longitude in the eastern Navka Region of Venus. The crater, which is approximately 8 kilometers (5 miles) in diameter, displays a butterfly symmetry pattern. The ejecta pattern most likely results from an oblique impact, where the impactor came from the south and ejected material to the north.

Voir l'image PIA00474: Venus - Impact Crater in Eastern Navka Region sur le site de la NASA.

PIA00253: Venus - Sinuous Channel

This full resolution radar mosaic from Magellan at 49 degrees south latitude, 273 degrees east longitude of an area with dimensions of 130 by 190 kilometers (81 by 118 miles), shows a 200 kilometer (124 mile) segment of a sinuous channel on Venus. The channel is approximately 2 kilometers (1.2 miles) wide. These channel-like features are common on the plains of Venus. In some places they appear to have been formed by lava which may have melted or thermally eroded a path over the plains' surface. Most are 1 to 3 kilometers (0.6 to 2 miles) wide. They resemble terrestrial rivers in some respects, with meanders, cutoff oxbows, and abandoned channel segments. However, Venus channels are not as tightly sinuous as terrestrial rivers. Most are partly buried by younger lava plains, making their sources difficult to identify. A few have vast radar-dark plains units associated with them, suggesting large flow volumes. These channels appear to be older than other channel types on Venus, as they are crossed by fractures and wrinkle ridges, and are often buried by other volcanic materials. In addition, they appear to run both upslope and downslope, suggesting that the plains were warped by regional tectonism after channel formation. Resolution of the Magellan data is about 120 meters (400 feet).

Voir l'image PIA00253: Venus - Sinuous Channel sur le site de la NASA.

PIA00262: Venus - Landslide in Navka Region

The Magellan spacecraft has observed remnant landslide deposits apparently resulting from the collapse of volcanic structures. This Magellan radar image is centered about 25.4 degrees south latitude and 308 degrees east longitude in the southwestern Navka Region of Venus. The image shows a 17.4 kilometer (10.8 mile) diameter volcanic dome on the plains. The dome is approximately 1.86 kilometers (1.2 mile) in height and it has a slope of about 23 degrees. The northwest and northeast flanks of the dome have collapsed to form landslides that have deposited debris on the plains. The image shows an area 110 kilometers (68 miles) across and 100 kilometers (62 miles) in length.

Voir l'image PIA00262: Venus - Landslide in Navka Region sur le site de la NASA.

PIA00219: Venus - Lada Terra Region

This is a Magellan radar image mosaic of part of Venus, centered at 51 degrees south latitude, 21 degrees east longitude. Each pixel, or picture element, represents 225 meters. The scene is approximately 200 kilometers (124 miles) east to west by 160 kilometers (99 miles) north to south. Running from west to east across the center of the image is part of a 1,200 kilometer (744 miles) long by 20 kilometer (12 mile) wide lava channel in the Lada Terra region of Venus. Numerous streamlined structures within the channel attest to the very high temperature, very fluid lavas (resulting in both thermal and mechanical erosion) responsible for carving the channel.

Voir l'image PIA00219: Venus - Lada Terra Region sur le site de la NASA.

PIA00087: Lavinia Region Ridge Belts, Plains and Lava Flows

This is a Magellan full resolution radar mosaic of the Lavinia region of Venus. The mosaic is centered at 50 degrees south latitude, 345 degrees east longitude, and spans 540 kilometers (338 miles) north to south and 900 kilometers (563 miles) east to west. As with all Magellan images acquired thus far, the illumination of the radar is from the left hand side of the image. This area shows a diverse set of geologic features. The bright area running from the upper right to the lower left is interpreted as part of a belt of ridges, formed by compression and thickening of the upper layers of the planet. The areas between ridges suggest flooding by radar dark (and thus presumably) smoother lavas. The varied texture of the lavas can be seen in the mottled appearance of the plains which are cut by the ridges; brighter, rougher flows are also quite common. The particularly bright flows in the lower right corner are the northern extension of Mylitta Fluctus. The bright ridges adjacent to Mylitta Fluctus at the bottom center of the image also appear to have been affected by the volcanic activity. Some of these bright features have been interpreted as down dropped areas roughly 5 kilometers (3 miles) wide. This would imply a region of extension where the crust has been pulled apart and thus was more easily flooded by the later lava flows. The thinner fractures running from the upper left seem to end at the ridge belt in the center of this mosaic. These thinner fractures are a continuation of a pattern seen throughout much of Lavinia and suggest a pattern of compression over a very large region. At the bottom of the image, overlying the ridges, is an impact crater 10 to 15 kilometers (6 to 10 miles) in diameter. The double or overlapped crater structure and asymmetrical ejecta pattern suggests that the incoming body broke up shortly before it hit, leaving closely spaced craters. The placement of the crater on top of the ridges implies it is younger than the ridges; in fact, the crater may be one of the youngest features in this image.

Voir l'image PIA00087: Lavinia Region Ridge Belts, Plains and Lava Flows sur le site de la NASA.

PIA00217: Arecibo/Magellan Composite of Quetzalpetlatl Corona

This composite image was created by inserting approximately 70 orbits of Magellan data into an image obtained at the Arecibo, Puerto Rico radiotelescope and shows a geologically complex region in the southern hemisphere of Venus. The region is centered on 65 degrees south, 359 degrees east and is about 1500 x 1500 km (900 x 900 miles) in extent. The large oval feature in the lower half of the image is Quetzalpetlatl Corona, approximately 700 km (420 miles) in diameter. Coronae are circular to oval regions defined by an annulus of ridges and are centers for tectonic and volcanic activity. Tectonic activity is largely observed in a relatively narrow rim region, which in this image is defined by a complex lineated terrain that surrounds much of the corona. Bright and dark volcanic flows are seen throughout the corona and surrounding terrain. Small shield volcanoes, 1-20 km (0.6-12 miles) in diameter, are seen near the southern limit of the Magellan data image. Narrow linear troughs (seen in the image as bright lines) trend to the north-northwest of Quetzalpetlatl.

Voir l'image PIA00217: Arecibo/Magellan Composite of Quetzalpetlatl Corona sur le site de la NASA.

PIA00100: Venus - Fractured Somerville Crater in Beta Regio

This Magellan radar image is of a 'half crater' located in the rift between Rhea and Theia Montes in Beta Regio on Venus. The unnamed crater is 37 kilometers (23 miles) in diameter and is located at 29.9 degrees north latitude and 282.9 degrees east longitude. It has been cut by many fractures or faults since it was formed by the impact of a large asteroid. The eastern half of the crater was destroyed during the formation of a fault valley that is up to 20 kilometers (12 miles) wide and apparently quite deep. A north-south profile through the very center of this crater is visible as a result of the down dropping and removal of the eastern half of the crater. Magellan scientists expect to get a better view of the crater's geological features during a later mapping cycle of Venus.

Voir l'image PIA00100: Venus - Fractured Somerville Crater in Beta Regio sur le site de la NASA.

PIA00089: Venus - Eistla Region

This Magellan image is of an area located in the Eistla Region of Venus in the southern hemisphere and is centered at 5.5 degrees east longitude, 18 degrees south latitude. It is 122 kilometers (76 miles) across east to west and 107 kilometers (66 miles) north to south. North is at the top of the image. Shown is an unusual volcanic edifice unlike all others previously observed. It is approximately 66 kilometers (41 miles) across at the base and has a relatively flat, slightly concave summit 35 kilometers (22 miles) in diameter. The sides of the edifice are characterized by radiating ridges and valleys that impart a fluted appearance. To the west, the rim of the structure appears to have been breached by dark lava flows that emanated from a shallow summit pit approximately 5 kilometers (3 miles) in diameter and traveled west along a channel approximately 5 kilometers wide and 27 kilometers (17 miles) long. A series of coalescing, collapsed pits 2 to 10 kilometers (1.2 to 6.2 miles) in diameter are located 10 kilometers (6 miles) west of the summit. The edifice and western pits are circumscribed by faint, concentric lineaments up to 70 kilometers (43 miles) in diameter. A series of north northwest trending graben are deflected eastward around the edifice; the interplay of these graben and the fluted rim of the edifice produce a distinctive scalloped pattern in the image. Several north northwest trending lineaments cut directly across the summit region. This peculiar volcanic construct is located 25 to 30 kilometers (15 to 19 miles) north of Alpha Regio, a highly deformed region of tessera terrain. A collection of at least six similar volcanoes has been observed near Thetis Regio, a region of tessera within Aphrodite Terra. Thus, these unusual constructs tentatively appear to be spatially associated with regions of tessera. A tessera is a complex, deformed terrain on Venus consisting of at least two sets of intersecting ridges and troughs. The implications of this spatial association on the unusual morphology of these constructs are being investigated.

Voir l'image PIA00089: Venus - Eistla Region sur le site de la NASA.

PIA00210: Venus - Golubkina Crater

This image of the Venusian crater Golubkina, a 340 kilometer (20.4 miles) diameter impact crater located at about 60.5 degrees north latitude, 287.2 degrees east longitude, contains Magellan data mosaiced with a Soviet Venera 15/16 radar image of the same feature. The Magellan part of the image (right) reveals details of the geology of the crater such as the central peak, the inner terraced walls, and the extremely smooth floor of the crater. The smoothness of the floor may be due to pounding of volcanic lava flows in the crater floor. The rough, blocky morphology of the crater ejecta and the sharp terraced crater wall suggest that this feature is relatively young. The Soviet data have a resolution of 102 km (0.601.2 miles); the Magellan data have a resolution of about 120 meters (400 feet).

Voir l'image PIA00210: Venus - Golubkina Crater sur le site de la NASA.

PIA00477: Venus - Possible Remnants of a Meteoroid in Lakshmi Region

This full resolution mosaiced image covers an area of approximately 100 kilometers by 120 kilometers (62 by 74 miles) and is located in the Lakshmi region of Venus at 47 degrees north latitude and 334 east longitude. Due to the dense Venusian atmosphere, primary impact craters of less than a 3 kilometer (2 mile) diameter are nonexistent. The dark circular region and associated central bright feature in this image are thought to be the remnants of a meteoroid smaller than the size necessary to create an impact crater entering the atmosphere at a low velocity (approximately 350 meters/second.) The central bright feature appears to be a cluster of small secondary impacts, ejecta and debris from the original meteor that broke up in the atmosphere. Even though most of the meteorite did not hit the surface, the atmospheric shock wave could be great enough to modify the surrounding region. One explanation for this radar dark circular formation, called dark margins, could be that the shock wave was energetic enough to pulverize the surface (smooth surfaces generally appear radar dark.) Another explanation is that the surface could be blanketed by a fine material that was formed by the original meteor's breakup through the atmosphere. More than half of the impact craters on Venus have associated dark margins, and most of these are prominently located left of center of the crater. This is another effect which could be caused by the dense atmosphere of Venus.

Voir l'image PIA00477: Venus - Possible Remnants of a Meteoroid in Lakshmi Region sur le site de la NASA.

PIA00149: Venus - Maxwell Montes and Cleopatra Crater

This Magellan full-resolution image shows Maxwell Montes, and is centered at 65 degrees north latitude and 6 degrees east longitude. Maxwell is the highest mountain on Venus, rising almost 11 kilometers (6.8 miles) above mean planetary radius. The western slopes (on the left) are very steep, whereas the eastern slopes descend gradually into Fortuna Tessera. The broad ridges and valleys making up Maxwell and Fortuna suggest that the topography resulted from compression. Most of Maxwell Montes has a very bright radar return; such bright returns are common on Venus at high altitudes. This phenomenon is thought to result from the presence of a radar reflective mineral such as pyrite. Interestingly, the highest area on Maxwell is less bright than the surrounding slopes, suggesting that the phenomenon is limited to a particular elevation range. The pressure, temperature, and chemistry of the atmosphere vary with altitude; the material responsible for the bright return probably is only stable in a particular range of atmospheric conditions and therefore a particular elevation range. The prominent circular feature in eastern Maxwell is Cleopatra. Cleopatra is a double-ring impact basin about 100 kilometers (62 miles) in diameter and 2.5 kilometers (1.5 miles) deep. A steep-walled, winding channel a few kilometers wide breaks through the rough terrain surrounding the crater rim. A large amount of lava originating in Cleopatra flowed through this channel and filled valleys in Fortuna Tessera. Cleopatra is superimposed on the structures of Maxwell Montes and appears to be undeformed, indicating that Cleopatra is relatively young.

Voir l'image PIA00149: Venus - Maxwell Montes and Cleopatra Crater sur le site de la NASA.

PIA00470: Venus - Complex Crater 'Buck' in Navka Region

This complex crater in the Navka region of Venus was mapped by Magellan on September 26-27, 1990 during orbits 459 and 460. The crater has a diameter of 22 kilometers (13.6 miles) and is located at latitude 5.75 degrees south, longitude 349.6 degrees east. It has the terraced walls, flat radar-dark floor, and central peak that are characteristic of craters classified as 'complex.' The central peak on its floor is unusually large. Flow-like deposits extend beyond the limits of the coarser rim deposits on its west and southwest. Like about half of the craters mapped by Magellan to date, it is surrounded by a local, radar-dark halo. Buck, the proposed name for this crater honors Pearl S. Buck, American author (1892-1973). Proposed names for all features on planetary bodies are provisional until formally adopted by the International Astronomical Union.

Voir l'image PIA00470: Venus - Complex Crater 'Buck' in Navka Region sur le site de la NASA.

PIA00222: Venus - Lower-level Nightside Clouds As Seen By NIMS

These images are two versions of a near-infrared map of lower-level clouds on the night side of Venus, obtained by the Near Infrared Mapping Spectrometer aboard the Galileo spacecraft as it approached the planet February 10, 1990. Taken from an altitude of about 22,000 miles above the planet, at an infrared wavelength of 2.3 microns (about three times the longest wavelength visible to the human eye) the map shows an area of the turbulent, cloudy middle atmosphere some 30-33 miles above the surface, 6-10 miles below the visible cloudtops. With a spatial resolution of about 13 miles, this is the sharpest image ever obtained of the mid-level clouds of Venus. The image to the left shows the radiant heat from the lower atmosphere (about 400 degrees Fahrenheit) shining through the sulfuric acid clouds, which appear as much as 10 times darker than the bright gaps between clouds. This cloud layer is at about - 30 degrees Fahrenheit, at a pressure about 1/2 Earth's atmospheric pressure. This high-resolution map covers a 40- degree-wide sector of the Northern Hemisphere. The several irregular vertical stripes are data dropouts. The right image, a modified negative, represents what scientists believe would be the visual appearance of this mid-level cloud deck in daylight, with the clouds reflecting sunlight instead of blocking out infrared from the hot planet and lower atmosphere. Near the equator, the clouds appear fluffy and blocky; farther north, they are stretched out into East-West filaments by winds estimated at more than 150 mph, while the poles are capped by thick clouds at this altitude. The Near Infrared Mapping Spectrometer (NIMS) on the Galileo spacecraft is a combined mapping (imaging) and spectral instrument. It can sense 408 contiguous wavelengths from 0.7 microns (deep red) to 5.2 microns, and can construct a map or image by mechanical scanning. It can spectroscopically analyze atmospheres and surfaces and construct thermal and chemical maps. Designed and operated by scientists and engineers at the Jet Propulsion Laboratory, NIMS involves 15 scientists in the U.S., England, and France. The Galileo Project is managed for NASA's Office of Space Science and Applications by JPL; its mission is to study the planet Jupiter and its satellites and magnetosphere after multiple gravity-assist flybys at Venus and the Earth.

Voir l'image PIA00222: Venus - Lower-level Nightside Clouds As Seen By NIMS sur le site de la NASA.

PIA00250: Venus - Wanda Crater in Akna Montes

This Magellan full-resolution images show the northern part of the Akna Montes (mountains) of Venus. The Akna range is a north-south trending ridge belt that forms the western border of the elevated smooth plateau of Lakshmi Planum (plains). The Lakshmi plateau plains are formed by extensive volcanic eruptions and are bounded by mountain chains on all sides. The plains appear to be deformed near the mountains. This suggests that some of the mountain building activity occurred after the plains formed. An impact crater (Official International Astronomical Union name 'Wanda,' mapped first by the Soviet Venera 15/16 mission in 1984 at low resolution) with a diameter of 22 kilometers (14 miles) was formed by the impact of an asteroid in the Akna mountains. The crater has a rugged central peak and a smooth radar-dark floor, probably volcanic material. The crater does not appear to be much deformed by later crustal movement that uplifted the mountains and crumpled the plains. Material from the adjacent mountain ridge to the west, however, appears to have collapsed into the crater. Small pits seen to the north of the crater may be volcanic collapse pits a few kilometers across (1-2 miles). The ridge of the Akna mountains immediately to the west of the crater is 8 kilometers wide (5 miles). The area imaged is approximately 200 kilometers long and 125 kilometers wide (130 by 80 miles). This area is centered at 71.5 degrees north latitude, 324 degrees east longitude. The resolution of the Magellan radar system is 120 meters (400 feet). At this latitude the radar views the surface from an angle of 23 degrees off vertical, creating a perspective as though a viewer were looking at the scene from the right (east) at an angle of 23 degrees above the surface.

Voir l'image PIA00250: Venus - Wanda Crater in Akna Montes sur le site de la NASA.

PIA00479: Venus - Complex Crater 'Dickinson' in NE Atalanta Region

This Magellan image is centered at 74.6 degrees north latitude and 177.3 east longitude, in the northeastern Atalanta Region of Venus. The image is approximately 185 kilometers (115 miles) wide at the base and shows Dickinson, an impact crater 69 kilometers (43 miles) in diameter. The crater is complex, characterized by a partial central ring and a floor flooded by radar-dark and radar-bright materials. Hummocky, rough-textured ejecta extend all around the crater, except to the west. The lack of ejecta to the west may indicate that the impactor that produced the crater was an oblique impact from the west. Extensive radar-bright flows that emanate from the crater's eastern walls may represent large volumes of impact melt, or they may be the result of volcanic material released from the subsurface during the cratering event.

Voir l'image PIA00479: Venus - Complex Crater 'Dickinson' in NE Atalanta Region sur le site de la NASA.

PIA00468: Venus - 'Transitional' Crater

During orbits 423 through 424 on 22 September 1990, Magellan imaged this impact crater that is located at latitude 10.7 degrees north and longitude 340.7 degrees east. This crater is shown as a representative of Venusian craters that are of the proper diameter (about 15 kilometers) to be 'transitional' in their morphology between 'complex' and irregular' craters. Complex craters account for about 96 percent of all craters on Venus with diameters larger than about 15 kilometers; they are thought to have been formed by the impact of a large, more or less intact, mass of asteroidal material that has not been excessively effected during its passage through the dense Venusian atmosphere. Complex craters are characterized by circular rims, terraced inner wall slopes, well developed ejecta deposits, and flat floors with a central peak or peak ring. Irregular craters make up about 60 percent of the craters with diameters less than about 15 kilometers. Irregular craters are thought to form as the result of the impact of asteroidal projectiles that have been aerodynamically crushed and fragmented during their passage through the atmosphere. Irregular craters are characterized by irregular and/or discontinuous rims and hummocky or multiple floors. The 'transitional' crater shown here has a somewhat circular rim like larger complex craters, but has the hummocky floor and asymmetric ejecta characteristic of smaller irregular craters.

Voir l'image PIA00468: Venus - 'Transitional' Crater sur le site de la NASA.

PIA00241: Venus - Lakshmi Planum and Maxwell Montes

This Magellan full resolution radar image is centered at 65 degrees north latitude, zero degrees east longitude, along the eastern edge of Lakshmi Planum and the western edge of Maxwell Montes. The plains of Lakshmi are made up of radar-dark, homogeneous, smooth lava flows. Located near the center of the image is a feature previously mapped as tessera made up of intersecting 1- to 2-km (0.6 to 1.2 miles) wide graven. The abrupt termination of dark plains against this feature indicates that it has been partially covered by lava. Additional blocks of tessera are located along the left hand edge of the image. A series of linear parallel troughs are located along the southern edge of the image. These features, 60- to 120-km (36- to 72- miles) long and 10- to 40- km (6- to 24- miles) wide are interpreted as graben. Located along the right hand part of the image is Maxwell Montes, the highest mountain on the planet, rising to an elevation of 11.5 km (7 miles) and is part of a series of mountain belts surrounding Lakshmi Planum. The western edge of Maxwell shown in this image rises sharply, 5.0 km (3.0 miles), above the adjacent plains in Lakshmi Planum. Maxwell is made up of parallel ridges 2- to 7-km (1.2- to 4.2 miles) apart and is interpreted to have formed by compressional tectonics. The image is 300 km (180 miles) wide.

Voir l'image PIA00241: Venus - Lakshmi Planum and Maxwell Montes sur le site de la NASA.

PIA00461: Venus - Mosaic of Bahet and Onatah Coronae

This mosaic of Magellan data in the Fortuna region of Venus, centered at 49 degrees north latitude, 2 degrees longitude, shows two coronae. Coronae are large circular or oval structures first identified in Soviet radar images of Venus. The structure on the left, Bahet Corona, is about 230 kilometers (138 miles) long and 150 kilometers (90 miles) across. A portion of Onatah Corona, over 350 kilometers (210 miles) in diameter, can be seen on the right of the mosaic. Both features are surrounded by a ring of ridges and troughs, which in places cut more radially-oriented fractures. The centers of the features also contain radial fractures as well as volcanic domes and flows. Coronae are thought to form due to the upwelling of hot material from deep in the interior of Venus. The two coronae may have formed at the same time over a single upwelling, or may indicate movement of the upwelling or the upper layers of the planet to the west over time. A 'pancake' dome, similar to low-relief domes see in the southern hemisphere, is located just to the southwest of Bahet. Resolution of the Magellan data is about 120 meters (400 feet).

Voir l'image PIA00461: Venus - Mosaic of Bahet and Onatah Coronae sur le site de la NASA.

PIA00466: Venus - Large Impact Crater in the Eistla Region

This Magellan image shows an impact crater in the central Eistla Region of the equatorial highlands of Venus. It is centered at 15 degrees north latitude and 5 degrees east longitude. The image is 76.8 kilometers (48 miles) wide. The crater is slightly irregular in platform and approximately 6 kilometers (4 miles) in diameter. The walls appear terraced. Five or six lobes of radar-bright ejecta radiate up to 13.2 kilometers (8 miles) from the crater rim. These lobes are up to 3.5 kilometers (2 miles) in width and form a "starfish" pattern against the underlying radar-dark plains. The asymmetric pattern of the ejecta suggests the angle of impact was oblique. The alignment of two of the ejecta lobes along fractures in the underlying plains is apparently coincidental.

Voir l'image PIA00466: Venus - Large Impact Crater in the Eistla Region sur le site de la NASA.

PIA00248: Venus - Aphrodite Terra

Landslides on Venus! The image on the left was taken in late November of 1990 during Magellan's first trip around Venus. The image on the right was taken July 23, as the Magellan spacecraft passed over the region for the second time. Each image is 24 kilometers (14.4 miles) across and 38 kilometers (23 miles) long, and is centered at 2 degrees south latitude and 74 degrees east longitude. This pair of Magellan images shows a region in Aphrodite Terra, within a steeply sloping valley that is cut by many fractures. In the center of the image on the right, a bright, flow-like area can be seen extending to the west (left) of a bright fracture. The bright, rough area has appeared and the fracture has changed position in the 8 months since the first image was made. A 'Venusquake' may have occurred, producing a new scarp and causing a landslide (the bright area) to form. This is the first evidence of active tectonics occurring on other planets in the solar system. Resolution of the Magellan data is 120 meters (400 feet).

Voir l'image PIA00248: Venus - Aphrodite Terra sur le site de la NASA.

PIA00201: Venus - Volcanic features in Atla Region

This Magellan image from the Atla region of Venus shows several types of volcanic features and superimposed surface fractures. The area in the image is approximately 350 kilometers (217 miles) across, centered at 9 degrees south latitude, 199 degrees east longitude. Lava flows emanating from circular pits or linear fissures form flower-shaped patterns in several areas. A collapse depression approximately 20 kilometers by 10 kilometers (12 by 6 miles) near the center of the image is drained by a lava channel approximately 40 kilometers (25 miles) long. Numerous surface fractures and graben (linear valleys) criss-cross the volcanic deposits in north to northeast trends. The fractures are not buried by the lavas, indicating that the tectonic activity post-dates most of the volcanic activity.

Voir l'image PIA00201: Venus - Volcanic features in Atla Region sur le site de la NASA.

PIA00482: Venus - Dark Volcanic Lava Flows

This scene, which covers an area of 75 kilometers (46 miles) by 45 kilometers (28 miles), shows an area of dark volcanic lava flows overlying the brighter surrounding plains which are thought to have been formed from older flows. Some of the dark flows terminate on the narrow bright sinuous feature to the right of the image and it is assumed that they originate from eruptions at fissures located along this bright feature. The image is located at latitude 4.6 degrees North and longitude 331.8 East. The horizontal banding is a processing artifact in this photo made from the first orbit after the start of systematic mapping.

Voir l'image PIA00482: Venus - Dark Volcanic Lava Flows sur le site de la NASA.

PIA00485: Venus - A Large Elongated Caldera 'Sacajawea Patera

This Magellan image reveals Sacajawea Patera, a large, elongate caldera located in Western Ishtar Terra on the smooth plateau of Lakshmi Planum. The image is centered at 64.5 degrees North latitude and 337 degrees East longitude. It is approximately 420 kilometers (252 miles) wide at the base. Sacajawea is a depression approximately 1-2 kilometers (0.6-1.2 miles) deep and 120 x 215 kilometers (74 x 133 miles) in diameter; it is elongate in a southwest-northeast direction. The depression is bounded by a zone of circumferential curvilinear structures interpreted to be graben and fault scarps. These structures are spaced 0.5-4 kilometers (0.3-2.5 miles) apart, are 0.6-4.0 kilometers (0.4-2.5 miles) in width and up to 100 kilometers (62 miles) in length. Extending up to approximately 140 kilometers (87 miles) in length from the southeast of the patera is a system of linear structures thought to represent a flanking rift zone along which the lateral injection and eruption of magma may have occurred. A shield edifice 12 kilometers (7 miles) in diameter with a prominent central pit lies along the trend of one of these features. The impact crater Zlata, approximately 6 kilometers (4 miles) in diameter is located within the zone of graben to the northwest of the patera. Few flow features are observed in association with Sacajawea, possibly due to age and state of degradation of the flows. Mottled bright deposits 4-20 kilometers (2.5-12 miles) in width are located near the periphery and in the center of the patera floor within local topographic lows. Diffuse patches of dark material approximately 40 kilometers (25 miles) in width are observed southwest of the patera, superposed on portions of the surrounding graben. The formation of Sacajawea is thought to be related to the drainage and collapse of a large magma chamber. Gravitational relaxation may have caused the resultant caldera to sag, producing the numerous faults and graben that circumscribe the patera. Regions of complex, highly deformed tessera-like terrain are located north and east of the patera and are seen in the upper portion of the image.

Voir l'image PIA00485: Venus - A Large Elongated Caldera 'Sacajawea Patera sur le site de la NASA.

PIA00098: Close-up view of Yavine Corona

The view shows Yavine Corona, a 500-km-wide asymmetric feature at latitude 5 degrees S., longitude 248.5 degrees; looking northeast. Coronae are roughly circular, volcanic features believed to form over hot upwellings of magma within the Venusian mantle. Yavine corona contains 2 novae; nova are circular hills having stellate fractures or grabens.

This is a three-dimensional perspective view of Venusian Terrains composed of reduced resolution left-looking synthetic-aperture radar images merged with altimetry data from the Magellan spacecraft.

Voir l'image PIA00098: Close-up view of Yavine Corona sur le site de la NASA.

PIA00206: Venus - Beta Regio

This portion of a Magellan radar image strip shows a small region on Venus 20 kilometers (12.4 miles) wide and 75 km (50 miles) long on the east flank of a major volcanic upland called Beta Regio. The image is centered at 23 degrees north latitude and 286.7 degrees east longitude. The ridge and valley network in the middle part of the image is formed by intersecting faults which have broken the Venusian crust into a complex, deformed type of surface called tessera, the Latin word for tile. The parallel mountains and valleys resemble the Basin and Range Province in the western United States. The irregular dark patch near the top of the image is a smooth surface, probably formed by lava flows in a region about 10 km (6 miles) across. Similar dark surfaces within the valleys indicate lava flows that are younger than the tessera giving an indication of the geologic time relationships of the events that formed the present surface. The image has a resolution of 120 meters (400 feet).

Voir l'image PIA00206: Venus - Beta Regio sur le site de la NASA.

PIA00096: Three-dimensional perspective views of Venusian Terrains composed of reduced resolution left-looking synthetic-aperture radar images merged with altimetry data from the Magellan spacecraft.

PIA00208: Venus - Rhea Mons Volcano

Two mosaiced pieces of Magellan image strips display the area east of the Rhea Mons volcano on Venus. This image is centered at about 32.5 degrees north latitude and 286.6 degrees east longitude. The mosaic is 47 kilometers (28 miles) wide and 135 km (81 miles) long. This region has been previously identified as "tessera" from Earth-based radar (Arecibo) images. The center of the image is dominated by a network of intersecting ridges and valleys. The radar bright north south trending features in this image range from 1 km (0.6 mile) to 3 km (1.8 miles) in length. The average spacing between these ridges is about 1.5 km (0.9 mile). The dark patches at the top of the image are smooth surfaces and may be lava flows located in lowlands between the higher ridge and the valley terrain. This image is a mosaic of two orbits obtained in the first Magellan radar test and played back to Earth to the Deep Space Network stations near Goldstone, Calif. and Canberra, Australia, respectively. The resolution of this image is approximately 120 meters (400 feet).

Voir l'image PIA00208: Venus - Rhea Mons Volcano sur le site de la NASA.

PIA00146: Venus - Ovda Regio

This image covers much of Ovda Regio, which forms the western part of Aphrodite Terra. It covers an area about 2,250 kilometers (1,386 miles) wide by 1,300 kilometers (800 miles) north to south, and ranges in latitude from 8 degrees north to 12 degrees south and in longitude from 62 degrees east to 90 degrees east. Ovda Regio is a highland region that rises over 4 kilometers (2.5 miles) above the surrounding plain. Magellan images show a complex surface, with several generations of structures. A pervasive fabric of irregular broad domes and ridges and associated curvilinear valleys was flooded by lava, then fractured. The circular feature surrounded by dark lava flows in the western part of the image is a caldera, or large volcanic collapse pit. Late-stage extension created long graben, or fault-bounded valleys, is best seen near the center of the image. The northern boundary of Ovda Regio is a steep, curvilinear mountain belt made up of long, narrow, rounded ridges. These ridges are similar in appearance to folded mountain belts on Earth. Several impact craters, such as the circular features on the western margin of the image, are scattered across the area. The bright area in the southeast part of the image indicates the presence of a radar-reflective mineral such as pyrite. Most of the highland areas on Venus display a similar bright signal. Each pixel of this image covers an area on the surface 675 meters (2,215 feet) across, representing a 9- times reduction in resolution compared to full-scale resolution data.

Voir l'image PIA00146: Venus - Ovda Regio sur le site de la NASA.

PIA00251: Venus - Stereoscopic Images of Volcanic Domes

This Magellan image depicts a stereoscopic pair of an area on Venus with small volcanic domes. Stereoscopic images of Venus offer exciting new possibilities for scientific analysis of Venusian landforms, such as the domes shown here, impact craters, graben -- long rifts bounded by faults -- and other geologic features. Stereopsis, or a three-dimensional view of this scene, may be obtained by viewing with a stereoscope. One may also cut this photograph into two parts and look at the left image with the left eye and the right image with the right eye; conjugate images (the same features) should be about 5 centimeters (2 inches) apart when viewing. This area is located at 38.4 degrees south latitude and 78.3 degrees east longitude. The incidence, or look, angle of the left image is 28.5 degrees and that of the right image is 15.6 degrees. Radar illumination for both images comes from the left. A small dome at left center is about 140 meters (464 feet) high and 6 kilometers (3.7 miles) wide. Other domes with smaller relief can be perceived in three dimensions. At the smaller incidence angle used to acquire the image on the right, radar brightness is more sensitive to small changes in topography. This enhances the visibility of many of the domes in this scene.

Voir l'image PIA00251: Venus - Stereoscopic Images of Volcanic Domes sur le site de la NASA.

PIA00148: Venus - Mead Crater

This Magellan image mosaic shows the largest (275 kilometers in diameter [170 miles]) impact crater known to exist on Venus at this point in the Magellan mission. The crater is located north of Aphrodite Terra and east of Eistla Regio at latitude 12.5 degrees north and longitude 57.4 degrees east, and was imaged during Magellan orbit 804 on November 12, 1990. The Magellan science team has proposed to name this crater Mead, after Margaret Mead, the American Anthropologist (1901- 1978). All Magellan-based names of features on Venus are, of course, only proposed until final approval is given by the International Astronomical Union-Commission on Planetary Nomenclature. Mead is classified as a multi-ring crater with its innermost, concentric scarp being interpreted as the rim of the original crater cavity. No inner peak-ring of mountain massifs is observed on Mead. The presence of hummocky, radar-bright crater ejecta crossing the radar-dark floor terrace and adjacent outer rim scarp suggests that the floor terrace is probably a giant rotated block that is concentric to, but lies outside of, the original crater cavity. The flat, somewhat brighter inner floor of Mead is interpreted to result from considerable infilling of the original crater cavity by impact melt and/or by volcanic lavas. To the southeast of the crater rim, emplacement of hummocky ejecta appears to have been impeded by the topography of preexisting ridges, thus suggesting a very low ground-hugging mode of deposition for this material. Radar illumination on this and all other Magellan image products is from the left to the right in the scene.

Voir l'image PIA00148: Venus - Mead Crater sur le site de la NASA.

PIA00471: Venus - Complex Lava Flows at Sif Mons

This is a full resolution mosaic centered at 25 degrees north latitude, 351 east longitude. The region is approximately 160 kilometers (100 miles) across. It shows a series of complex lava flows which emerge from the northern flank of Sif Mons, a large volcano just to the south. Several of the flows occupy narrow troughs formed by long fractures. A sequence of events that can be inferred from this image is the formation of the dark background plains by eruptions of extremely fluid volcanic material, and the formation of the small shield volcanoes on the plains surface that can be seen in the upper left part of the image. Next, the region was domed upward probably by heat from the interior of Venus that ultimately caused magmas to break out from the surface near the summit regions forming the Sif volcanic structure and its associated flank eruptions which can be seen in this image.

Voir l'image PIA00471: Venus - Complex Lava Flows at Sif Mons sur le site de la NASA.

PIA00476: Venus - Multi-Floor Irregular Crater

This Magellan image shows an irregular crater of approximately 14- kilometer (8.7-mile) mean diameter. The crater is actually a cluster of four separate craters that are in rim contact. The noncircular rims and multiple, hummocky floors are probably the result of the breakup and dispersion of an incoming meteoroid during passage through the dense Venusian atmosphere. After breaking up, the meteoroid fragments impacted nearly simultaneously, creating the crater cluster. The area shown is 40 kilometers (25 miles) in width and 76 kilometers (47 miles) in length, it is centered at -21.4 degrees latitude, 335.2 degrees longitude in the northern Lavinia Region of Venus.

Voir l'image PIA00476: Venus - Multi-Floor Irregular Crater sur le site de la NASA.

PIA00211: Venus - Phoebe Region

This Magellan radar image is of part of the Phoebe region of Venus. It is a mosaic of parts of revolutions 146 and 147 acquired in the first radar test on Aug. 16, 1990. The area in the image is located at 291 degrees east longitude, 19 degrees south latitude. The image shows an area 30 kilometers (19.6 miles) wide and 76 km (47 miles) long. On the basis of Pioneer Venus and Arecibo data, it is known that two major rift zones occur in southern Phoebe Regio and that they terminate at about 20 to 25 degrees south latitude, about 2,000 km (1,240 miles) apart. This image is of an area just north of the southern end of the western rift zone. The region is characterized by a complex geologic history involving both volcanism and faulting. Several of the geologic units show distinctive overlapping or cross cutting relationships that permit identification and separation of geologic events and construction of the geologic history of the region. The oldest rocks in this image form the complexly deformed and faulted, radar bright, hilly terrain in the northern half. Faults of a variety of orientations are observed. A narrow fault trough (about one-half to one km (three tenths to six tenths of a mile) wide is seen crossing the bright hills near the lower part in the middle of the image. This is one of the youngest faults in the faulted, hilly unit as it is seen to cut across many other structures. The fault trough in turn appears to be embayed and flooded by the darker plains that appear in the south half of the image. These plains are interpreted to be of volcanic origin. The dark plains may be formed of a complex of overlapping volcanic flows. For example, the somewhat darker region of plains in the lower left (southwest) corner of the image may be a different age series of plains forming volcanic lava flows. Finally, the narrow bright line crossing the image in its lower part is interpreted to be a fault which cross cuts both plains units and is thus the youngest event in the sequence. These relationships show the interplay of volcanic activity and faulting that have influenced this region and a number of other regions on Venus.

Voir l'image PIA00211: Venus - Phoebe Region sur le site de la NASA.

PIA00101: Artemis Corona (C2-MIDR)

This spectacular Magellan image is centered on 30 degrees south latitude, 135 degrees east longitude, spans 3500 kilometers (2170 miles) from east to west (left to right), and shows the near-circular trough of Artemis Chasma. Its circular shape and size (2100 km or 1302 miles in diameter) make Artemis the largest corona identified to date on the surface of Venus. Artemis could encompass most of the U.S. from the Front Range of the Rockies (near Denver) to the West Coast and is approximately twice the diameter of the next-smaller corona Heng-O. Coronae are characterized by a ring of concentric features surrounding an interior which typically contains fractures of varying orientations and volcanic features ranging from individual flows and small (100 kilometers [62 mile]) shield volcanoes. Artemis contains complex systems of fractures, numerous flows and small volcanoes, and at least two impact craters, the larger of which is located in the lower left (southwest) quadrant of the feature. The ring of fractures that defines Artemis forms a steep trough with raised rims approximately 120 kilometers (74 miles) wide and with as much as 2.5 kilometers (1.6 miles) of relief from the rim crest to the bottom of the trough. Most coronae are thought to be related to upwelling of hot material from the interior of Venus in the form of plumes or diapirs, and Artemis may be an extensional trough related to such an upwelling event. Raised-rim troughs are most commonly found to be extensional features (those formed by forces which tend to pull apart the crust and lithosphere of a planet) but the unusual size and circularity of Artemis have led to the alternate suggestion that it may be a zone of intense compression and underthrusting, similar to oceanic subduction zones on Earth. Magellan scientists are currently examining this feature in detail to determine which, if either, of these hypotheses is correct.

Voir l'image PIA00101: Artemis Corona (C2-MIDR) sur le site de la NASA.

PIA00088: Venus - Stein Triplet Crater

The Magellan synthetic aperture radar (SAR) imaged this unique 'triplet crater,' or 'crater field' during orbits 418-421 on 21 September 1990. These craters are 14 kilometers, 11 kilometers, and 9 kilometers in diameter, respectively, and are centered at latitude -30.1 degrees south and longitude 345.5 degrees east. The Magellan Science Team has proposed the name Stein for this crater field after the American author, Gertrude Stein. This name has not yet been approved by the International Astronomical Union. The crater field was formed on highly fractured plains. The impacts generated a considerable amount of low viscosity 'flows' thought to consist largely of shock-melted target material along with fragmented debris from the crater. The three craters appear to have relatively steep walls based on the distortion in the image of the near and far walls of the craters in the Magellan radar look direction (from the left). The flow deposits from the three craters extend dominantly to the northeast (upper right).

Voir l'image PIA00088: Venus - Stein Triplet Crater sur le site de la NASA.

PIA00264: Venus - Volcano With Massive Landslides

This Magellan full-resolution mosaic which covers an area 143 by 146 kilometers (89 by 91 miles) is centered at 55 degrees north latitude, 266 degrees east longitude. The bright feature, slightly south of center is interpreted to be a volcano, 15-20 kilometers (9.3 to 12.4 miles) in diameter with a large apron of blocky debris to its right and some smaller aprons to its left. A preferred explanation is that several massive catastrophic landslides dropped down steep slopes and were carried by their momentum out into the smooth, dark lava plains. At the base of the east-facing or largest scallop on the volcano is what appears to be a large block of coherent rock, 8 to 10 kilometers (5 to 6 miles) in length. The similar margin of both the scallop and block and the shape in general is typical of terrestrial slumped blocks (masses of rock which slide and rotate down a slope instead of breaking apart and tumbling). The bright lobe to the south of the volcano may either be a lava flow or finer debris from other landslides. This volcanic feature, characterized by its scalloped flanks is part of a class of volcanoes called scalloped or collapsed domes of which there are more than 80 on Venus. Based on the chute-like shapes of the scallops and the existence of a spectrum of intermediate to well defined examples, it is hypothesized that all of the scallops are remnants of landslides even though the landslide debris is often not visible. Possible explanations for the missing debris are that it may have been covered by lava flows, the debris may have weathered or that the radar may not be recognizing it because the individual blocks are too small

Voir l'image PIA00264: Venus - Volcano With Massive Landslides sur le site de la NASA.

PIA00218: Venus - Interior of Ovda Regio

This Magellan image shows part of the interior of Ovda Regio, one of the large highlands ringing the equator of Venus. Several tectonic events formed this complex block fractured terrain. An underlying fabric of ridges and valleys strikes northeast southwest. These ridges are spaced 10 to 20 kilometers (6 to 12 miles) apart and may have been caused by shortening of the crust at right angles to this trend. These structures are cut by thoroughgoing extension fractures trending northwest-southeast, suggesting a later episode of northeast southwest extension. Lastly, the largest valleys, particularly the 20 kilometer (12 mile) wide one extending across the image, were filled with dark material, probably lava. The complex internal fabric of Ovda Regio attests to a long history of tectonic deformation. This image, centered approximately at 1 degree south, 81 degrees east, measures 225 kilometers (140 miles) by 150 kilometers (90 miles) and was acquired by Magellan in November 1990.

Voir l'image PIA00218: Venus - Interior of Ovda Regio sur le site de la NASA.

PIA00086: Mosaic of Large Impact Craters

One of the most useful Magellan standard data products is the full resolution mosaic, the F-MIDR (Full-Resolution Mosaiced Image Data Record). These products are mosaics of about 500 kilometer (300 mile) segments of 30 or more individual image strips. This image is an F-MIDR made from orbits 376 to 407, obtained between September 15 and September 19, 1990, part of the first orbits in which the Magellan flight team operated the radar system in the mapping mode. The mosaic is centered at 27 degrees south latitude, 339 degrees longitude, in the Lavinia region of Venus. Three large impact craters with diameters ranging from 37 kilometers (23 miles) to 50 kilometers (30 miles) can be seen located in a region of fractured plains. The craters show many features typical of meteorite impact craters, including rough, radar-bright ejecta, terraced inner walls and central peaks. Numerous domes of probable volcanic origin can be seen in the southeastern corner of the mosaic. The domes range in diameter from 1-12 kilometers (0.6-7 miles), and some have central pits typical of volcanic shields or cones. Resolution of the Magellan data is about 120 meters (400 feet).

Voir l'image PIA00086: Mosaic of Large Impact Craters sur le site de la NASA.

PIA00263: Venus - Landslide Deposits

The Magellan spacecraft has observed remnant landslide deposits apparently resulting from the collapse of volcanic structures. This image, centered at 45.2 degrees south latitude, 201.4 degrees east longitude, shows a collapse deposit 70 kilometers (43 miles) across. The bright, highly textured deposit near the center of the image probably consists of huge blocks of fractured volcanic rock, many as large as several hundred meters across. A remnant of the volcano itself, about 20 kilometers (12.4 miles) across, is seen at the center of the image. The distorted radar appearance of the volcano is a result of extremely steep slopes on the 'scars' from which the landslide material originated. A field of numerous small volcanic domes can be seen in the northern half of the image. The bright irregular lineaments trending to the north-northwest are ridges caused by regional tectonic deformation of the upper layers of the Venusian crust.

Voir l'image PIA00263: Venus - Landslide Deposits sur le site de la NASA.

PIA00097: Close-up view of Atete Corona

The view is a close-up of Atete Corona, a 600-km-long and 450-km-wide feature at latitude 16 degrees S., longitude 244 degrees; looking north. Coronae are roughly circular volcanic features believed to form over hot upwellings of magma within the Venusian mantle. The north end of the corona bounds Parga Chasma, a 0-3 km deep depression that spans 1,870 km connecting Themis Regio (latitude 35 degrees S., longitude 285 degrees) and Maat Mons (latitude 0 degree, longitude 195 degrees).

This is a three-dimensional perspective view of Venusian Terrains composed of reduced resolution left-looking synthetic-aperture radar images merged with altimetry data from the Magellan spacecraft.

Voir l'image PIA00097: Close-up view of Atete Corona sur le site de la NASA.

PIA00209: Venus - 3D Perspective of Golubkina Crater

This three dimensional representation of brightness variations in a Magellan radar image of Golubkina crater enhances the structural features of the crater. Golubkina is 34 kilometers (20.4 miles) in diameter, and is located at about 60.5 degrees north latitude, 287.2 degrees east longitude. Golubkina is characterized by terraced inner walls and a central peak, typical of large impact craters on the Earth, Moon and Mars. The terraced inner walls form at late stages in the formation of an impact crater, due to collapse of the initial cavity formed by the meteorite impact. The central peak forms due to rebound of the inner crater floor.

Voir l'image PIA00209: Venus - 3D Perspective of Golubkina Crater sur le site de la NASA.

PIA00099: East Part of Sapas Mons with Flooded Crater

This Magellan image centered near 9.6 degrees north latitude, 189.5 degrees east longitude of an area 140 kilometers (87 miles) by 110 kilometers (68 miles) covers part of the eastern flank of the volcano Sapas Mons on the western edge of Atla Regio. The bright lobate features along the southern and the western part of the image, oriented in northeast to southwest directions, are lava flows that are rough at the 12.6 centimeter wavelength of the radar. These flows range in width from 5 kilometers to 25 kilometers (3 to 16 miles) with lengths of 50 kilometers to 100 kilometers (31 to 62 miles), extending off the area shown here. Additional radar-dark (smooth) flows are also present. The radar-bright linear structures in the northwest part of the image are interpreted to be faults and fractures possibly associated with the emplacement of magma in the subsurface. Located near the center of the image is a 20 kilometer (12 mile) diameter impact crater. This crater is superimposed on a northeast/southwest trending fracture while the southern part of the crater's ejecta blanket is covered by a 6 kilometer (4 mile) wide radar-bright lava flow. These relations indicate that the crater post dates an episode of fracturing and is older than the lava flows covering its southern edge. This is one of only a few places on Venus in which an impact crater is seen to be covered by volcanic deposits.

Voir l'image PIA00099: East Part of Sapas Mons with Flooded Crater sur le site de la NASA.

PIA00207: Venus - Magellan and Arecibo Comparison

This image shows a comparison between a Magellan image (right) and the highest resolution Earth-based radar image of Venus, obtained by the U.S. National Astronomy and Ionosphere Center's Arecibo Observatory in Puerto Rico. The small white box in the Arecibo image on the left corresponds to the Magellan image. This portion of a Magellan radar image strip shows a small region on the east flank of a major volcanic upland called Beta Regio. The image is centered at 23 degrees north latitude and 286.7 degrees east longitude. The ridge and valley network in the middle part of the image is formed by intersecting faults which have broken the Venusian crust into a complex deformed type of surface called tessera, the Latin word for tile. The parallel mountains and valleys resemble the Basin and Range Province in the western United States. The irregular dark patch near the top of the image is a smooth surface, probably formed by lava flows in a region about 10 km (6 miles) across. Similar dark surfaces within the valleys indicate lava flows that are younger than the tessera. The Arecibo image contains probable impact craters, many faults, volcanic flows and tessera regions that will be mapped in detail by Magellan. The Magellan image has a resolution of 120 meters, (400 feet). The image segment is 20 km (12.4 miles) wide and 150 km (90 miles) long. The Arecibo image has a resolution of 1 3 km (0.6 1.8 miles) and is approximately 900 km (550 miles) across. The National Astronomy and Ionosphere Center is operated by Cornell University under a management agreement with the National Science Foundation with some support from NASA.

Voir l'image PIA00207: Venus - Magellan and Arecibo Comparison sur le site de la NASA.

PIA00483: Venus - Outflow Channel in South Navka

This SAR image from the southern portion of Navka (24.4-25.3 degrees south latitude, 338.5-340.5 degrees east longitude) is a mosaic of twelve Magellan orbits that covers 180 kilometers (108 miles) in width and 78 kilometers (47 miles) in length. In the center of this image are two bright deposits running north to south. These deposits outline an outflow channel that flowed from a 60-km diameter crater that is to the south of the channel. Inside the outflow channel and outlined by 'bathtub ring' deposits are small cones, most likely of volcanic origin. At the end of the outflow channel, where one would expect the smallest particles to be deposited, are specular features which may represent sand dunes. Seasat and space shuttle radar images of sand dunes on Earth also show specular reflections from smooth dune faces that are near-normal to the radar beam. Other evidence for aeolian activity are the dark and bright windstreaks running east to west that form behind cones. Notice how the wind changes direction from a southeast-northwest flow at the right of the image to an east-west flow at the eastern edge of the outflow channel.

Voir l'image PIA00483: Venus - Outflow Channel in South Navka sur le site de la NASA.

PIA00467: Venus - Lavinia Region

This image is centered at approximately 29.6 degrees south latitude and 341 degrees east longitude in the Lavinia Region of Venus. Volcanic vent areas in this part of the plains west of Alpha Regio consist of domes and pits up to nearly 3 kilometers across. Extending eastward these features are sinuous channels, most of which are about 10 kilometers or more long. The channels narrow away from the pits and for most of their lengths are about 1 kilometer in diameter. The nearest planetary analogues for these features are sinuous rilles on the moon. These have been explained as lava channels and/or the result of lava erosion. On Earth lava channels form by downhill drainage of a lava flow leaving a channel behind. Lava may continue to flow in the channel once it has formed. However, lava channels on Earth are normally only a few meters or tens of meters wide. On the other hand, they may be the result of lava erosion. This is a process that only normally occurs to a limited extent on Earth because melting is inhibited by the cool upper layers of the planet. Also, lavas rarely flow turbulently enough to cause mechanical erosion. On Venus the surface materials are already at high temperatures, thus assisting thermal erosion and it is possible that lavas which may flow turbulently are more readily available than on Earth. Resolution of the Magellan data is about 120 meters (400 feet).

Voir l'image PIA00467: Venus - Lavinia Region sur le site de la NASA.

PIA00249: Venus - Danu Montes and Lakshmi Planum

Southwest Lakshmi Planum (plains) is bounded on the south by the Danu Montes (mountains). Lakshmi Planum is an elevated plateau plain that is bounded on all sides by mountain chains. Here, the Danu mountains have an angular fractured appearance. Chasms slice diagonally across the mountains in the lower left (southwest) corner of the image. Because of the steep slopes and the local relief of the mountains of several kilometers (2-3 miles, these fault-bounded troughs appear to zig-zag through the mountains when, in fact, they are probably straight if viewed from above. The radar view provides a perspective that would place the viewer's eye to the right, 27 degrees above the horizon. Thus, slopes facing to the right can be seen completely, though dark, and slopes facing away to the left appear shortened, often seen only as thin bright lines. In the center of the image is a low volcanic dome (20 kilometers (12 miles) in diameter. This type of volcanic feature frequently occurs on the low plains. This dome on the edge of Lakshmi is deformed and faulted where it has been affected by the forces that created the Danu mountains. The image is 75 kilometers (46 miles) on a side. The center is at 60 degrees north latitude, 324.5 degrees east longitude.

Voir l'image PIA00249: Venus - Danu Montes and Lakshmi Planum sur le site de la NASA.

PIA00460: Venus - Venera 8 Landing Site in Navka Region

This image is a mosaic of 24 orbits of the Navka region of Venus. The image is centered at about 10 degrees south latitude and 335 degrees east longitude. The image is about 400 km (240 miles) across. 'Behepa 8' marks the approximate landing site of the Soviet Venera 8 lander, which took measurements at the surface of Venus in 1972. The Venera 8 lander measured granitic or continental-like materials at the landing site. Magellan data reveals the landing site to lie in a region of plains cut by tectonic ridges and troughs. Volcanic domes and flows are seen throughout the region. Studying the regional setting of the Venera landing sites is important in linking information about surface composition to surface morphology seen in radar images. Resolution of the Magellan data is about 120 meters (400 feet).

Voir l'image PIA00460: Venus - Venera 8 Landing Site in Navka Region sur le site de la NASA.

PIA00240: Venus - Lakshmi Planum

This image is a full-resolution mosaic of several Magellan images and is centered at 61 degrees north latitude and 341 degrees east longitude. The image is 250 kilometers wide (150 miles). The radar smooth region in the northern part of the image is Lakshmi Planum, a high plateau region roughly 3.5 kilometers (2.2 miles) above the mean planetary radius. Lakshmi Planum is ringed by intensely deformed terrain, some of which is shown in the southern portion of the image and is called Clotho Tessera. The 64-kilometer (40 mile) diameter circular feature in the image is a depression called Siddons and may be a volcanic caldera. This view is supported by the collapsed lava tubes surrounding the feature. By carefully studying this and other surrounding images scientists hope to discover what tectonic and volcanic processes formed this complex region. The solid black parts of the image represent data gaps that may be filled in by the Magellan extended mission.

Voir l'image PIA00240: Venus - Lakshmi Planum sur le site de la NASA.

PIA00469: Venus - Complex Network of Narrow Fractures Near Hestia Rupes Region

PIA00247: Venus - Left and Right Looking Images of Lavinia Region

These two Magellan radar images are centered about 60.5 degrees south latitude and 348.8 degrees east longitude in the eastern Lavinia Region of Venus. The images, which are 110 kilometers (68 miles) in length and 130 kilometers (81 miles) in width, are full resolution mosaics of 14 orbits. The bottom image was made during cycle 2 of the Magellan mission when the radar was looking to the right of the spacecraft and at an angle of 25 degrees. The top image was made at the beginning of the mission when the radar was looking to the left and at an angle of 20 degrees. The mission data at the lower left of the top image represents the beginning of radar mapping during cycle 1. Both images show an area with interesting troughs, which are collapse features. In the bottom image, the north-south trending trough has a bright side on the left and a darkside on the right, while in the top image it is reversed. This is because the side of the trough sloping away from the radar appears dark while the side facing the radar appears bright. Since the radar was looking from the right in the bottom image and from the left in the second image, the bright and dark sides for the trough are reversed between the top and bottom images. It is very useful to obtain right-looking and left-looking images of the same area because features may not be visible from the opposite look direction. For instance, there are some fractures that can only be seen in one image. In addition, the different incidence angles obtained in cycle 2 of the mission, will allow scientists to better understand the nature of the Venus surface. Resolution of the Magellan data is about 120 meters (400 feet).

Voir l'image PIA00247: Venus - Left and Right Looking Images of Lavinia Region sur le site de la NASA.

PIA00150: Nova Superposed on Yavine Corona

The view shows a 100-km-wide nova superposed on Yavine Corona, a 500-km-wide asymmetric feature at latitude 5 degrees S., longitude 248.5 degrees; looking northeast. Coronae are roughly circular, volcanic features believed to form over hot upwellings of magma within the Venusian mantle. Yavine corona contains 2 novae; nova are circular hills with star-shaped fractures. The view is a close-up of the southern nova showing its fractures to be grabens or fault bound depressions. Novae may represent an intermediate stage in coronae formation.\

This is a three-dimensional perspective view of Venusian Terrains composed of reduced resolution left-looking synthetic-aperture radar images merged with altimetry data from the Magellan spacecraft.

Voir l'image PIA00150: Nova Superposed on Yavine Corona sur le site de la NASA.