951 Gaspra
Bill Arnett
last updated: 2002 Aug 20
http://www.seds.org/billa/tnp/gaspra.html
"Gaspra's surface is covered with impact craters. From the number of small craters on its surface, we can estimate that Gaspra is about 200 million years old."
243 Ida and Dactyl
Bill Arnett
last updated: 2002 Sep 08
http://www.seds.org/billa/tnp/ida.html
"Dactyl (right) is about 1.6 x 1.2 km, surprisingly round for such a small body. It orbits Ida at approximately 90 km.
"The discovery that one out of two asteroids observed up close is in fact a binary system has reinvigorated an old debate about the frequency of binary asteroids. But more data is needed before the controversy can really be resolved...
"Interestingly, while the spectra of Ida and Dactyl are very similar they are nevertheless distinctly different; Dactyl is not simply a chunk of Ida. It is thought that the binary system may have formed during the collision and breakup that created the Koronis family.
"The surfaces of Ida and Dactyl are heavily cratered and therefore apparently quite old. But dynamical calculations indicate that the whole Koronis family is relatively young. Such calculations also indicate that objects the size of Dactyl may not be to survive for more than 100 million years or so. Perhaps the heavy cratering took place at the time of the breakup that created the Koronis family rather than the 4 billion years ago as is usually the case for such surfaces."
Mathilde Images
http://near.jhuapl.edu/Mathilde/images.html
"The part of the asteroid shown is about 59 kilometers (36 miles) across, and the scale is approximately 230 meters (780 feet) per pixel. The surface is heavily cratered, and the large shadowed area on the left may be a single impact gouge well over 10 kilometers (6 miles) deep. The angular form of the edge of the shadowed area suggests that large impacts may have spalled large pieces off the asteroid. This asteroid is very dark, reflecting only about 4% of the light falling on it, but was imaged easily by the sensitive NEAR multispectral camera... The surface exhibits many large craters, including the deeply shadowed one at the center, which is estimated to be more than 10 kilometers (6 miles) deep. The shadowed, wedge-shaped feature at the lower right is another large crater viewed obliquely. The angular shape of the upper left limb of the asteroid results from the rim of a third large crater viewed edge-on. The bright mountainous feature at the far left may be the rim of a fourth large crater emerging from the shadow. The angular shape is believed to result from a violent history of impacts... This portion of Mathilde shows numerous impact craters, ranging from over 30 km to less than 0.5 km (18.. 0.3 miles) in diameter. Raised crater rims suggest that some of the material ejected from these craters traveled only short distances before falling back to the surface; straight sections of some crater rims indicate the influence of large faults or fractures on crater formation... Mathilde appears to be the abundance of very large craters: Mathilde has at least 5 craters larger than 20 km in diameter on the roughly 60% of the body viewed during the encounter... Mathilde's irregular shape results from a long history of severe collisions with smaller asteroids. The largest visible crater is 30 km (19 miles) in diameter."
[this is related to message 10; found a bunch of stuff, which I'm going to plaster into another topic]
Koronis Family Asteroids Rotation Lightcurve Observing Program
Dr. Stephen M. Slivan
MIT, Dept. of Earth, Atmospheric, and Planetary Sciences
Last modified 2006 May 29
http://www.koronisfamily.com/