Discoverer

G. N. Neujmin - 1916

Diameter (km)

19 x 12 x 11

Mass (kg)

1*10^{^16}

Rotation period (hrs)

7.042

Orbital period (yrs)

3.29

Semimajor axis (AU)

2.20997

Orbital eccentricity

0.17331

Orbital Inclination (deg)

4.10284

Albedo

?

Type

S

Images of Gaspra

This first image of asteroid 951 Gaspra was taken by the Galileo spacecraft on October 29, 1991, from a distance of 16,200 kilometers. The Sun is shining from the right. The illuminated part of the asteroid is about 16 by 12 kilometers. The surface shows many craters; two large facets about 8 kilometers across appear on the limb of the asteroid at top and bottom right.

The smallest craters in this view are about 300 meters across. Gaspra rotates in a counter-clockwise direction in just over 7 hours; its north pole is near the upper left corner of the lighted part of the asteroid.

This montage of 11 images taken by the Galileo spacecraft as it flew by the asteroid Gaspra on October 29, 1991, shows Gaspra growing progressively larger in the field of view of Galileo's solid-state imaging camera as the spacecraft approached the asteroid. Sunlight is coming from the right. Gaspra is roughly 17 kilometers long, 10 kilometers wide. The earliest view (upper left) was taken 5 3/4 hours before closest approach when the spacecraft was 164,000 kilometers from Gaspra, the last (lower right) at a range of 16,000 kilometers, 30 minutes before closest approach.

Gaspra spins once in roughly 7 hours, so these images capture almost one full rotation of the asteroid. Gaspra spins counterclockwise; its north pole is to the upper left, and the 'nose' which points upward in the first image, is seen rotating back into shadow, emerging at lower left, and rotating to upper right. Several craters are visible on the newly seen sides of Gaspra, but none approaches the scale of the asteroid's radius. Evidently, Gaspra lacks the large craters common on the surfaces of many planetary satellites, consistent with Gaspra's comparatively recent origin from the collisional breakup of a larger body.

This picture of asteroid 951 Gaspra is a mosaic of two images taken by the Galileo spacecraft from a range of 5,300 kilometers, some 10 minutes before closest approach on October 29, 1991. The Sun is shining from the right; phase angle is 50 degrees. The resolution, about 54 meters/pixel, is the highest for the Gaspra encounter and is about three times better than that in the view released in November 1991. Additional images of Gaspra remain stored on Galileo's tape recorder, awaiting playback in November.

Gaspra is an irregular body with dimensions about 19 x 12 x 11 kilometers. The portion illuminated in this view is about 18 kilometers from lower left to upper right. The north pole is located at upper left; Gaspra rotates counterclockwise every 7 hours. The large concavity on the lower right limb is about 6 kilometers across, the prominent crater on the terminator, center left, about 1.5 kilometers. A striking feature of Gaspra's surface is the abundance of small craters. More than 600 craters, 100-500 meters in diameter are visible here. The number of such small craters compared to larger ones is much greater for Gaspra than for previously studied bodies of comparable size such as the satellites of Mars.

Gaspra's very irregular shape suggests that the asteroid was derived from a larger body by nearly catastrophic collisions. Consistent with such a history is the prominence of groove-like linear features, believed to be related to fractures. These linear depressions, 100-300 meters wide and tens of meters deep, are in two crossing groups with slightly different morphology, one group wider and more pitted than the other. Grooves had previously been seen only on Mars's moon Phobos, but were predicted for asteroids as well. Gaspra also shows a variety of enigmatic curved depressions and ridges in the terminator region at left.

These two color views of the asteroid Gaspra were produced by combining three images taken through violet, green, and infrared filters by the Galileo spacecraft on October 29, 1991, from a distance of about 16,000 kilometers. The view on the left shows Gaspra in approximately true color; the surface is covered with rocks that are somewhat less grey than those on Earth's moon.

In the version on the right, the colors were enhanced to bring out the muted color variations on the asteroid and to increase the ability to discriminate between surface features. The subtle variations in color may be due to slight differences in rock composition or to differences in the texture of the surface layer. These possibilities should be resolved once the rest of Galileo's Gaspra data are played back in 1992. Gaspra is about 19 by 12 by 11 kilometers and irregular in shape.

This montage shows asteroid 951 Gaspra (top) compared with Deimos (lower left) and Phobos (lower right), the moons of Mars. The three bodies are shown at the same scale and nearly the same lighting conditions. Gaspra is about 17 kilometers long. All three bodies have irregular shapes, due to past catastrophic conditions. However their surfaces appear remarkably different, possibly because of differences in composition but most likely because of very different impact histories.

The Phobos and Deimos images were obtained by the Viking Orbiter spacecraft in 1977; the Gaspra image is the best of a series obtained by the Galileo spacecraft on October 29, 1991.

(Credit: NASA-JPL)