Asteroid 951 Gaspra was discovered by Grigoriy N. Neujamin in 1916. Neujamin named Gaspra after a Black Sea retreat that was visited by contemporaries such as Tolstoy and Gorky. Gaspra was just a another small asteroid that was given very little attention until it was discovered that the trajectory of the Galileo spacecraft would take it close to Gaspra. Following this discovery, observers through out the world made Gaspra a prime target of study. Gaspra was found to have an elongated shape with a rotational period of 7.04 hours.
On October 29, 1991 Galileo came within 1,600 km (1,000) miles of Gaspra. They passed each other at 8 km per second. This was the first time that a spacecraft made a fly-by of an asteroid. Gaspra is an irregular body with dimensions of about 20 x 12 x 11 km (12 x 7.5 x 7 miles). Its surface reflects approximately 20 percent of the sunlight striking it. Gaspra is classified as an S-type asteroid and is likely composed of metal-rich silicates and perhaps blocks of pure metal. It is a member of the Flora family.
Several craters are visible on Gaspra, but none approach the scale of the asteroid's radius. The fact that Gaspra is irregular in shape and that it lacks any large craters suggests that it has a comparatively recent origin from the collisional breakup of a larger body. Gaspra has probably been in its present state for the last 300 to 500 million years.
Gaspra in Color
(GIF, 170K)
This picture Gaspra is a combination of the
highest-resolution images and color information obtained by
the Galileo spacecraft. The Sun is shining from the right.
The subtle color variations on Gaspa's surface have
been exaggerated. Albedo
and color variations are associated with surface
topography. The
bluish areas are regions of slightly higher albedo and
tend to be associated with some of the crisper
craters and with ridges. The slightly reddish areas, apparently
concentrated in low areas, represent regions of somewhat
lower albedo. In general, such patterns can be explained in terms
of greater exposure of fresher rock in the brighter bluish areas and
the accumulation of some regolith
materials in the darker reddish areas. (Courtesy USGS/NASA/JPL).
Eleven Views of Gaspra
(GIF, 73K)
This set of 11 images shows Gaspra
growing progressively larger in the field of view of Galileo's
camera as the spacecraft approached the
asteroid. Sunlight is coming from the right.
The earliest view (upper left) was taken 5 3/4 hours before
closest approach when the spacecraft was 164,000 kilometers
(102,000 miles) from Gaspra, the last (lower right) at a range of
16,000 kilometers (10,000 miles), 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. (Courtesy NASA/JPL).
Gaspra Compared to Deimos and Phobos
(GIF, 93K)
This picture shows 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.
All 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. (Courtesy NASA/JPL).