LYCOS RETRIEVER 
951 Gaspra
built 236 days ago
Asteroid 951 Gaspra appears to be in an obliquity resonance with its spin increasing due to the Yarkovsky-O'Keefe-Radzievskii-Paddack effect (YORP effect, for short). Gaspra, an asteroid 5.8 km in radius, is a prograde rotator with a rotation period of 7.03 hours. A 3 × 106 year integration indicates that its orbit is stable over at least this time span. From its known shape and spin axis orientation and assuming a uniform density, Gaspra's axial precession period turns out to be nearly commensurate with its orbital precession period, which leads to a resonance condition with consequent huge variations in its obliquity. At the same time, its shape is such that the YORP effect is increasing its spin rate. YORP may be a reason for small asteroids entering resonances in the first place: they speed up or slow down and fall into resonances. The continued action of YORP probably ultimately causes asteroids to leave resonances, so that they are quasi-stable states.
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This picture of asteroid 951 Gaspra is a mosaic of two images taken by the Galileo spacecraft from a range of 5,300 kilometers (3,300 miles), 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 (12 x 7.5 x 7 miles). The portion illuminated in this view is about 18 kilometers (11 miles) from lower left to upper right.
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This picture of asteroid 951 Gaspra is a combination of the highest-resolution morphology and color information obtained by the Galileo spacecraft during its approach to the asteroid on October 29, 1991, while en route to Jupiter. The color has been exaggerated to show differences in surface composition. Asteroids are generally grey to slightly brown in color. Gaspra is a rough ellipsoid with dimensions of about 19 x 12 x 11 kilometers.
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This picture of asteroid 951 Gaspra is a combination of the highest-resolution morphology and color information obtained by the Galileo spacecraft during its approach to the asteroid on October 29, 1991. The Sun is shining from the right; phase angle is 50 degrees. The base image is the best black-and-white view of Gaspra (resolution 54 meters/pixel) on which are superimposed the subtle color variations constructed from violet, green, and near-infrared (1000 nanometers) inages taken in an earlier sequence at a resolution about 164 meters/pixel.
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Asteroid 951 Gaspra is shown here as a mosaic of two images taken by Galileo about 3300 miles away on 10/29/1991. About 11 miles long, its irregular shape is presumed to be derived from a much larger asteroid shattered in a catastrophic col lision.
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This picture of 951 Gaspra is an enhanced image based on data from the Galileo spacecraft as it approached on October 29, 1991. The base image is a black and white image upon which are superimposed subtle color variations constructed from violet, green, and near-infrared(1000nm) images taken in an earlier sequence. The subtle color variations have been artificially exaggerated; the surface looked fairly homogeneous. However, the subtle changes were there and were correlated with significant surface features. The bluish areas represent regions of slightly higher albedo, which ... absorb somewhat more strongly in the 1000 nm band, probably due to the mineral olivine. These bluish areas tend to be associated with some of the crisper craters and ridges.
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951 Gaspra