Minor Planets

In February 2000, asteroid studies took a remarkable jump forward when the Near Earth Asteroid Rendezvous (NEAR)-Shoemaker spacecraft, first of NASA's "Discovery" series of relatively low-cost space probes, went into orbit around the asteroid 433 Eros, an S-class asteroid about 8 × 8 × 21 mi (13 × 13 × 33 km) in size. NEAR-Shoemaker, the first spacecraft ever to orbit an asteroid, had already flown by the C-class, main-belt asteroid 253 Mathilde in 1997, taking high-resolution Figure 2. Illustration by Hans & Cassidy. Courtesy of Gale Group. images. After studying Eros from a safe distance for several months NEAR-Shoemaker executed a low-altitude flyby in October 2000, imaging the asteroid's surface at a resolution of about 1 yard per pixel. The spacecraft observed a stony, potato-shaped body about the size of Manhattan that was covered with regolith (impactchurned rock) similar to that observed on the Moon. On February 12, 2001, its planned goals all accomplished, NEAR-Shoemaker was directed to touch down gently on the surface of Eros. Not only did the probe take some 69 closeup images during its final approach, including a final image covering an area only 19 ft (6 m) across, but it survived the touchdown. (This was surprising because, as a purely interplanetary probe, it had not been designed to survive any form of direct contact with an asteroid.)

Analysis of X rays emitted by Eros during a solar flare and observed by NEAR-Shoemaker showed that the asteroid's composition closely resembled that of the chondritic meteorites, which are considered remnants of the early solar system. This has bolstered the theory that the asteroids, too, are primordial leftovers that have never been part of any planet.