This view of the asteroid 243 Ida is a mosaic of five image frames acquired by the Galileo spacecraft's solid-state imaging system at ranges of 3,057 to 3,821 kilometers (1,900 to 2,375 miles) on August 28, 1993, about 3-1/2 minutes before the spacecraft made its closest approach to the asteroid. Galileo flew about 2,400 kilometers (1,500 miles) from Ida at a relative velocity of 12.4 km/sec (28,000 mph). Asteroid and spacecraft were 441 million kilometers (274 million miles) from the Sun. Ida is the second asteroid ever encountered by a spacecraft. It appears to be about 52 kilometers (32 miles) in length, more than twice as large as Gaspra, the first asteroid observed by Galileo in October 1991. Ida is an irregularly shaped asteroid placed by scientists in the S class (believed to be like stony or stony iron meteorites). It is a member of the Koronis family, presumed fragments left from the breakup of a precursor asteroid in a catastrophic collision. This view shows numerous craters, including many degraded craters larger than any seen on Gaspra. The extensive cratering seems to dispel theories about Ida's surface being geologically youthful. This view also seems to rule out the idea that Ida is a double body. The south pole is believed to be in the darkside near the middle of the asteroid. The camera's clear filter was used to produce this extremely sharp picture. Spatial resolution is 31 to 38 meters (roughly 100 feet) per pixel. A 30-frame mosaic was taken to assure capturing Ida; its position was somewhat uncertain before the Galileo encounter. Galileo shuttered and recorded a total of 150 images in order to capture Ida 21 different times during a five hour period (about one rotation of the asteroid). Color filters were used at many of these times to allow reconstruction of color images. Playback to Earth of the remaining images is planned for April through June 1994. The Galileo project, whose primary mission is the exploration of the Jupiter system in 1995-97, is managed for NASA's Office of Space Science by the Jet Propulsion Laboratory.

Voir l'image PIA00135: Asteroid Ida - Five Frame Mosaic sur le site de la NASA.

PIA00333: Asteroid Ida and its Satellite Dactyl in Enhanced Color

During its examination of the asteroid Ida, the Galileo spacecraft returned images of a second object, Dactyl--the first confirmed satellite or moon of an asteroid; the much smaller moon is visible to the right of Ida. Asteroids are small interplanetary bodies of rock or metal that mostly orbit the Sun in a belt between Mars and Jupiter, but others are known elsewhere in the solar system. The Galileo spacecraft surveyed Ida in 1993 on its way to explore the Jupiter system in 1995-97. This color picture was made from images taken by the imaging system on the Galileo spacecraft about 14 minutes before its closest approach to asteroid 243 Ida on August 28, 1993. The range from the spacecraft was about 10,500 kilometers (6,500 miles). The images used are from the sequence in which Ida's moon 1993 (2433)1 Dactyl was discovered. This picture contains images through the 4100-angstrom (violet), 7560 A (infrared) and 9680 A (infrared) filters. The color is "enhanced" in the sense that the CCD camera is sensitive to near infrared wavelengths of light beyond human vision; a "natural" color picture of this asteroid would appear mostly gray. Shadings in the image indicate changes in illumination angle on the many steep slopes of this irregular body as well as subtle color variations due to differences in the physical state and composition of the soil (regolith). There are brighter areas, appearing bluish in the picture, around craters on the upper left end of Ida, around the small bright crater near the center of the asteroid, and near the upper right-hand edge (the limb). This combination of more reflected blue light and greater absorption of near infrared light, suggest a difference in the abundance or composition of iron-bearing minerals in these areas. Ida's moon also has a deeper near-infrared absorption and a different color in the violet than any area on this side of Ida. The moon is not identical in spectral properties to any area of Ida in view here, though its overall similarity in reflectance and general spectral type suggests that it is made of the same basic rock types. Resolved images of Ida over a full rotation period (4.633 h) allowed detailed shape models to be developed, yielding volumes of 16,000+ -1,900 km cubed for Ida (mean radius, 15.7 km) and 1.4 km cubed for Dactyl (mean radius, 0.7 km; Belton et al., 1995, Nature, v. 374, p. 785- 788). These images and other data collected by the Galileo spacecraft may allow scientists to determine whether these asteroids are pieces of bigger ones that at one time partly melted and differentiated (forming a dense metallic core and rocky crust) or whether these are pieces of material unaltered since their formation during the birth of the Solar System.

Voir l'image PIA00333: Asteroid Ida and its Satellite Dactyl in Enhanced Color sur le site de la NASA.

PIA00332: Ida and Gaspra

This picture shows the asteroids Ida (left) and Gaspra (right) to the same scale. These images were taken by the Galileo spacecraft while enroute to Jupiter. Gaspra was imaged on October 29, 1991 at a range of 3,300 miles (5,300 km). Ida was imaged on August 28, 1993 from a range of 1,900 to 2,400 miles (3,000 to 3,800 km). Both objects are irregular in shape. Gaspra is about 10.5 miles long (17 km), and Ida is 18.6 miles long and 6 to 8 miles wide (9.3 x 12.7 x 29.9 km). These asteroids are just two of the billions of such rocky and metallic objects that orbit the sun mainly between Mars and Jupiter. A small percentage orbit near the other planets. The irregular shapes of these objects suggests that they are "chips" derived from larger bodies by catastrophic collisions between asteroids. The surface of Ida and Gaspra are peppered by small craters, evidence of much smaller collisions. Craters are more abundant on Ida, thereby suggesting that it formed earlier than Gaspra. Both asteroids have linear depressions over a thousand feet wide in places and a hundred feet or so deep; these depressions may be where loose fragmental soil (the "regolith") has partly drained into fractures. These asteroids show evidence of having such a fragmental layer, which on Ida may be 165 to 330 feet (50 to 100 m deep). The fragmental debris layers on asteroids may one day prove invaluable to space miners, who may obtain asteroids everything from precious metals for use on Earth to water destined for use in space. Asteroids are also important to life on Earth because sometimes their orbits wander across Earth's and collisions ensue. About 2,000 asteroids larger than 0.6 miles across presently have orbits that cross or come close to Earth's orbit. Impacts with objects as large as Gaspra and Ida are very rare, but they have occurred in the past and are capable of causing mass extinctions of almost everything that lives on our planet. .

Voir l'image PIA00332: Ida and Gaspra sur le site de la NASA.

PIA00331: Nine Galileo Views in Exaggerated Color of Main-Belt Asteroid Ida

This set of color images of asteroid 243 Ida was taken by the imaging system on the Galileo spacecraft as it approached and raced past the asteroid on August 28, 1993. These images were taken through the 4100-angstrom (violet), 7560-angstrom (infrared) and 9680- angstrom (infrared) filters and have been processed to show Ida in exaggerated color to bring out subtle color contrasts caused by small variations in composition and surface microtexture of the asteroid's soil. In natural color Ida appears gray with slight overtones of red or brown. Stark shadows portray Ida's irregular shape, which changes its silhouetted outline when seen from different angles. More subtle shadings reveal surface topography (such as craters) and differences in the physical state and composition of the soil ("regolith"). Note in particular the color differences associated with the rims and floors of certain impact craters, which may have excavated to layers of slightly differing composition or may have ingested material from impactors of different compositions. Analysis of the images show that Ida is 58 kilometers long and 23 kilometers wide (36 x 14 miles). Ida is the first asteroid discovered to have a natural satellite, Dactyl (not shown here). Ida and Dactyl are heavily cratered by impacts with smaller asteroids and comets, including some of the same populations of small objects that bombard Earth. These data, combined with reflectance spectra from Galileo's near-infrared mapping spectrometer, may allow scientists to determine whether Ida is a relatively unaltered primitive object made of material condensed from the primordial Solar Nebula at the origin of the Solar System or whether it has been altered by strong heating--evidence interpreted so far suggests that Ida is a piece of a larger object that has been severely heated. Whereas heating and melting of large planets is well understood, the cause of heating of small asteroids is more enigmatic--it may have involved exotic processes that occurred only for a short time after the birth of the Sun and its planets.

Voir l'image PIA00331: Nine Galileo Views in Exaggerated Color of Main-Belt Asteroid Ida sur le site de la NASA.

PIA00137: Asteroid Ida - 6 Views Showing Rotation

This composite image shows the asteroid 243 Ida as seen from the Galileo spacecraft during its approach on August 28, 1993. The six views were shuttered through the camera's green filter and show Ida's rotation over a period of about 3 hours 18 minutes. The asteroid makes a complete rotation every 4 hours 38 minutes; therefore, this set of images spans about 3/4 of Ida's rotation period and shows most of Ida's surface. By combining the information in these views with that from the highest resolution images returned from the spacecraft in September 1993, the size and shape of this irregular body can now be determined accurately The asteroid appears to be about 58 kilometers (36 miles) long and about 23 kilometers wide, with a very irregular shape and volume of some 16,000 cubic kilometers. The images are arranged in chronological order from a time 3 hours 51 minutes before closest approach (upper left), through upper right, middle left, middle right lower left and lower right (33 minutes before closest approach). The six images show Ida at the same scale throughout. Ida's rotation axis is roughly vertical in these images, and the rotation causes the right-hand end of Ida to move toward the viewer as time progresses. The first image was taken from a range of about 171,000 km (106,000 miles) and provides an image resolution of about 1,700 meters per pixel (the highest resolution achieved for Ida is about 25 meters per pixel). The second, taken 70 minutes later, is from 119,000 kilometers, followed by 102,000 kilometers, 85,000 kilometers, 50,000 kilometers, and 25,000 kilometers. The features on Ida are less sharp in the earlier views because of the greater distances. Prominent in the middle three views is a deep depression across the short axis of the Asteroid. This feature tends to support the idea that Ida may have originally been formed from two or more separate large objects that collided softly and stuck together. Also visible in the lower left view is an apparent linear albedo or reflectance boundary. Color images yet to be returned from the Galileo spacecraft may help resolve the question of whether or not the two ends of Ida are made of different materials.

Voir l'image PIA00137: Asteroid Ida - 6 Views Showing Rotation sur le site de la NASA.

PIA00070: Asteroid Ida Rotation Sequence

This montage of 14 images (the time order is right to left, bottom to top) shows Ida as it appeared in the field of view of Galileo's camera on August 28, 1993. Asteroid Ida rotates once every 4 hours, 39 minutes and clockwise when viewed from above the north pole; these images cover about one Ida 'day.' This sequence has been used to create a 3-D model that shows Ida to be almost croissant shaped. The earliest view (lower right) was taken from a range of 240,000 kilometers (150,000 miles), 5.4 hours before closest approach. The asteroid Ida draws its name from mythology, in which the Greek god Zeus was raised by the nymph Ida.

Voir l'image PIA00070: Asteroid Ida Rotation Sequence sur le site de la NASA.

PIA00138: Asteroid Ida - Limb at Closest Approach

The Galileo imaging system captured this picture of the limb of the asteroid 243 Ida about 46 seconds after its closest approach on August 28, 1993, from a range of only 2480 kilometers. It is the highest-resolution image of an asteroid's surface ever captured and shows detail at a scale of about 25 meters per pixel. This image is one frame of a mosaic of 15 frames shuttered near Galileo's closest approach to Ida. Since the exact location of Ida in space was not well-known prior to the Galileo flyby, this mosaic was estimated to have only about a 50 percent chance of capturing Ida. Fortunately, this single frame did successfully image a part of the sunlit side of Ida. The area seen in this frame shows some of the same territory seen in a slightly lower resolution full disk mosaic of Ida returned from the spacecraft in September, 1993, but from a different perspective. Prominent in this view is a 2 kilometer deep "valley" seen in profile on the limb. This limb profile and the stereoscopic effect between this image and the full disk mosaic will permit detailed refinement of Ida's shape in this region. This high resolution view shows many small craters and some grooves on the surface of Ida, which give clues to understanding the history of this heavily impacted object. The Galileo project, whose primary mission is the exploration of the Jupiter system in 1995-97, is managed for NASA's Office of Space Science by the Jet Propulsion Laboratory.

Voir l'image PIA00138: Asteroid Ida - Limb at Closest Approach sur le site de la NASA.

PIA00069: Ida and Dactyl in Enhanced Color

This color picture is made from images taken by the imaging system on the Galileo spacecraft about 14 minutes before its closest approach to asteroid 243 Ida on August 28, 1993. The range from the spacecraft was about 10,500 kilometers (6,500 miles). The images used are from the sequence in which Ida's moon was originally discovered; the moon is visible to the right of the asteroid. This picture is made from images through the 4100-angstrom (violet), 7560 A (infrared) and 9680 A (infrared) filters. The color is 'enhanced' in the sense that the CCD camera is sensitive to near infrared wavelengths of light beyond human vision; a 'natural' color picture of this asteroid would appear mostly gray. Shadings in the image indicate changes in illumination angle on the many steep slopes of this irregular body as well as subtle color variations due to differences in the physical state and composition of the soil (regolith). There are brighter areas, appearing bluish in the picture, around craters on the upper left end of Ida, around the small bright crater near the center of the asteroid, and near the upper right-hand edge (the limb). This is a combination of more reflected blue light and greater absorption of near infrared light, suggesting a difference in the abundance or composition of iron-bearing minerals in these areas. Ida's moon also has a deeper near-infrared absorption and a different color in the violet than any area on this side of Ida. The moon is not identical in spectral properties to any area of Ida in view here, though its overall similarity in reflectance and general spectral type suggests that it is made of the same rock types basically. These data, combined with study of further imaging data and more detailed spectra from the Near Infrared Mapping Spectrometer, may allow scientists to determine whether the larger parent body of which Ida, its moon, and some other asteroids are fragments was a heated, differentiated object or made of relatively unaltered primitive chondritic material. The Galileo project, whose primary mission is the exploration of the Jupiter system in 1995-97, is managed for NASA's Office of Space Science by the Jet Propulsion Laboratory.

Voir l'image PIA00069: Ida and Dactyl in Enhanced Color sur le site de la NASA.

PIA00136: Asteroid Ida and Its Moon

This is the first full picture showing both asteroid 243 Ida and its newly discovered moon to be transmitted to Earth from the National Aeronautics and Space Administration's (NASA's) Galileo spacecraft--the first conclusive evidence that natural satellites of asteroids exist. Ida, the large object, is about 56 kilometers (35 miles) long. Ida's natural satellite is the small object to the right. This portrait was taken by Galileo's charge-coupled device (CCD) camera on August 28, 1993, about 14 minutes before the Jupiter-bound spacecraft's closest approach to the asteroid, from a range of 10,870 kilometers (6,755 miles). Ida is a heavily cratered, irregularly shaped asteroid in the main asteroid belt between Mars and Jupiter--the 243rd asteroid to be discovered since the first was found at the beginning of the 19th century. Ida is a member of a group of asteroids called the Koronis family. The small satellite, which is about 1.5 kilometers (1 mile) across in this view, has yet to be given a name by astronomers. It has been provisionally designated '1993 (243) 1' by the International Astronomical Union. ('1993' denotes the year the picture was taken, '243' the asteroid number and '1' the fact that it is the first moon of Ida to be found.) Although appearing to be 'next' to Ida, the satellite is actually in the foreground, slightly closer to the spacecraft than Ida is. Combining this image with data from Galileo's near-infrared mapping spectrometer, the science team estimates that the satellite is about 100 kilometers (60 miles) away from the center of Ida. This image, which was taken through a green filter, is one of a six-frame series using different color filters. The spatial resolution in this image is about 100 meters (330 feet) per pixel.

Voir l'image PIA00136: Asteroid Ida and Its Moon sur le site de la NASA.

PIA00330: Nine Galileo Views in Natural Color of Main-Belt Asteroid Ida

This set of color images of asteroid 243 Ida was taken by the imaging system on the Galileo spacecraft as it approached and raced past the asteroid on August 28, 1993. These images were taken through the 4100-angstrom (violet), 7560-angstrom (infrared) and 9680- angstrom (infrared) filters and have been processed to show Ida as it would appear to the eye in approximately natural color. The stark shadows portray Ida's irregular shape, which changes its silhouetted outline when seen from different angles. More subtle shadings reveal surface topography (such as craters) and differences in the physical state and composition of the soil ("regolith"). Analysis of the images show that Ida is 58 kilometers long and 23 kilometers wide (36 x 14 miles). Ida is the first asteroid discovered to have a natural satellite, Dactyl (not shown here). Both Ida and Dactyl are heavily cratered by impacts with smaller asteroids and comets, including some of the same populations of small objects that bombard Earth. These data, combined with reflectance spectra from Galileo's near-infrared mapping spectrometer, may allow scientists to determine whether Ida is a relatively unaltered primitive object made of material condensed from the primordial Solar Nebula at the origin of the Solar System or whether it has been altered by strong heating--evidence interpreted so far suggests that Ida is a piece of a larger object that has been severely heated. Whereas heating and melting of large planets is well understood, the cause of heating of small asteroids is more enigmatic--it may have involved exotic processes that occurred only for a short time after the birth of the Sun and its planets.

Voir l'image PIA00330: Nine Galileo Views in Natural Color of Main-Belt Asteroid Ida sur le site de la NASA.