PIA00479.jpg = 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.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.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.PIA00107: Venus - 3D Perspective View of Sapas Mons
Sapas Mons is displayed in the center of this computer-generated three-dimensional perspective view of the surface of Venus. The viewpoint is located 527 kilometers (327 miles) northwest of Sapas Mons at an elevation of 4 kilometers (2.5 miles) above the terrain. Lava flows extend for hundreds of kilometers across the fractured plains shown in the foreground to the base of Sapas Mons. The view is to the southeast with Sapas Mons appearing at the center with Maat Mons located in the background on the horizon. Sapas Mons, a volcano 400 kilometers (248 miles) across and 1.5 kilometers (0.9 mile) high is located at approximately 8 degrees north latitude, 188 degrees east longitude, on the western edge of Atla Regio. Its peak sits at an elevation of 4.5 kilometers (2.8 miles) above the planet's mean elevation. Sapas Mons is named for a Phoenician goddess. The vertical scale in this perspective has been exaggerated 10 times. Rays cast in a computer intersect the surface to create a three-dimensional perspective view. Simulated color and a digital elevation map developed by the U.S. Geological Survey are used to enhance small-scale structure. The simulated hues are based on color images recorded by the Soviet Venera 13 and 14 spacecraft. The image was produced by the Solar System Visualization project and the Magellan Science team at the JPL Multimission Image Processing Laboratory and is a single frame from a video released at the April 22, 1992 news conference.
Voir l'image PIA00107: Venus - 3D Perspective View of Sapas Mons 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.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.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.
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.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.
| | 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.
PIA00201.jpg = 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.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.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.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.
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.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.
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.PIA00478: Venus - Global View Centered at 180 degrees
This global view of the surface of Venus is centered at 180 degrees east longitude. Magellan synthetic aperture radar mosaics from the first cycle of Magellan mapping, and a 5 degree latitude-longitude grid, are mapped onto a computer-simulated globe to create this image. Data gaps are filled with Pioneer-Venus Orbiter data, or a constant mid-range value. The image was produced by the Solar System Visualization project and the Magellan Science team at the JPL Multimission Image Processing Laboratory.
Voir l'image PIA00478: Venus - Global View Centered at 180 degrees sur le site de la NASA.PIA00256: Venus - Simple Cylindrical Map of Surface (Eastern Half)
The eastern half of the planet is displayed in this simple cylindrical map of the surface of Venus. The left edge of the image is at 52.5 degrees east longitude, the right edge at 240 degrees east longitude. The top and bottom of the image are at 90 degrees north latitude and 90 degrees south latitude, respectively. Magellan synthetic aperture radar mosaics from the first cycle of Magellan mapping are mapped onto a rectangular latitude-longitude grid to create this image. Data gaps are filled with Pioneer Venus Orbiter altimetric data, or a constant mid-range value. Simulated color is used to enhance small-scale structure. The simulated hues are based on color images recorded by the Soviet Venera 13 and 14 spacecraft. The image was produced by the Solar System Visualization project and the Magellan science team at the JPL Multimission Image Processing Laboratory.
Voir l'image PIA00256: Venus - Simple Cylindrical Map of Surface (Eastern Half) 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.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.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.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.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.
PIA00480: Venus - Impact Crater 'Isabella
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.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.
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.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.
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.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.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.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.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.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.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.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.
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.