Waltzing past Mathilde.On its way to a 1999 rendezvous with a near-Earth asteroid Near-Earth asteroids (NEAs) are asteroids whose orbits are close to Earth's orbit. Some NEAs' orbits intersect Earth's so they pose a collision danger. On the other hand, NEAs are most easily accessible for spacecraft from Earth; in fact, some can be reached with much less fuel , a spacecraft late last month took some 500 snapshots of a tiny rock called 431 Mathilde. After viewing the images, which depict a battered rock pitted with craters, planetary scientists had one key question: Why does this asteroid still exist? The craft, known as NEAR (near-Earth asteroid rendezvous), spied five craters more than 20 kilometers in diameter gouged into the sunlit sun·lit adj. Illuminated by the sun. Adj. 1. sunlit - lighted by sunlight; "the sunlit slopes of the canyon"; "violet valleys and the sunstruck ridges"- Wallace Stegner sunstruck side of Mathilde, a potato-shaped body measuring about 50 km across. "This rock has been through collisional hell," says Joseph Veverka of Cornell University Cornell University, mainly at Ithaca, N.Y.; with land-grant, state, and private support; coeducational; chartered 1865, opened 1868. It was named for Ezra Cornell, who donated $500,000 and a tract of land. With the help of state senator Andrew D. , yet its heavily pockmarked pock·mark n. 1. A pitlike scar left on the skin by smallpox or another eruptive disease. 2. A small pit on a surface: The gophers left the lawn covered with pockmarks. tr.v. surface indicates it has survived for at least 2 billion years. An initial analysis of radio wave observations suggests a possible explanation. The data indicate that the dark rock has a low density, akin to that of a pile of sand or rubble loosely bound by gravity. When an object strikes such a body, notes Veverka, "it's like hitting a sponge." Rather than shattering Mathilde, the shock wave from the impact may be absorbed. NEAR has deepened another mystery about Mathilde, which resides in the belt of asteroids This is a list of numbered minor planets, nearly all of them asteroids, in sequential order. As of late September 2007 there are 164,612 numbered minor planets, and many more not yet numbered. Most asteroids are ordinary and not particularly noteworthy. lying between the orbits of Mars and Jupiter. Researchers had already known that the asteroid spins very slowly, once every 17 days. That's puzzling because the frequent collisions with debris from other asteroids would tend to make Mathilde spin faster. Scientists theorized that Mathilde might have been slowed by the gravity of a moon a few km in diameter, but NEAR found no such companion. The spacecraft, which came within 1,200 km of Mathilde--the closest photo shoot of any asteroid to date--also revealed that Mathilde appears the same inside and out. It reflects the same amount of sunlight, half as much as a chunk of charcoal, even from regions where a projectile projectile something thrown forward. projectile syringe see blow dart. projectile vomiting forceful vomiting, usually without preceding retching, in which the vomitus is thrown well forward. has dug deep into the rock. The uniformity indicates that the rock, classified as a C-type asteroid because it contains carbonaceous car·bo·na·ceous adj. Consisting of, containing, relating to, or yielding carbon. carbonaceous Adjective of, resembling, or containing carbon Adj. 1. material, is a pristine relic of the early solar system. |
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