Discoverer

J. Palisa - 1884

Diameter (km)

58 x 23

Mass (kg)

1*10^{^17}

Rotation period (hrs)

4.633

Orbital period (yrs)

4.84

Semimajor axis (AU)

2.86108

Orbital eccentricity

0.04614

Orbital Inclination (deg)

1.13664

Albedo

0.24

Type

S

Images of Ida and Dactyl

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. 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. 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.

This view of the asteroid 243 Ida was acquired by the Galileo spacecraft at ranges of 3,057 to 3,821 kilometers on August 28, 1993, about 3.5 minutes before the spacecraft made its close approach to the asteroid. This view shows numerous craters, many larger than any seen on Gaspra.

This is the first full picture showing both asteroid 243 Ida and its newly discovered moon to be transmitted to Earth from Galileo spacecraft-the first conclusive evidence that natural satellites of asteroids exist.

Ida, the large object, is about 56 kilometers 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.

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 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 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 per pixel.

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 fulldisk 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 fulldisk 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.

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 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 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.

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, 5.4 hours before closest approach.

On this image it is possible to see Dactyl's dark side that is illuminated by light reflected from Ida.

This is one early image of Dactyl.

This image is the first full picture showing both asteroid 243 Ida and its moon Dactyl transmitted to Earth from NASA's Galileo spacecraft. This portrait was taken about 14 minutes before Galileo's closest approach to the asteroid, from a range of 10,870 kilometers.

(Credit NASA/JPL