On 12 February this year, the Near Earth Asteroid Rendezvous (NEAR) Shoemaker spacecraft landed on the asteroid Eros. Three analyses of what it saw are published in this week's Nature, revealing a miniature world of surprising complexity, far removed from the common view of asteroids as featureless lumps of rock. Eros is strewn with large boulders that scientists say resulted from an impact that formed the 4.5 mile (7.6-kilometrer) wide 'Shoemaker' crater, the asteroid's main feature. The asteroid also has many mysterious 'ponds' of bluish dust. What caused these is unclear, but solar energy may have made the particles electrically charged, causing them to levitate out of the asteroid and settle on its surface.

The first detailed global mapping of an asteroid has found that most of the larger rocks strewn across asteroid Eros were ejected from a single crater in a meteorite collision perhaps a billion years ago. "One big impact spread all this debris," says NEAR team member Peter Thomas, a senior researcher in Cornell University's Department of Astronomy. "This observation is helping us start answering questions about how things work on the surface of an asteroid."

Craters and Boulders on Eros (Click image to enlarge)

Thomas' report on the crater is one of three papers detailing the first findings from the NEAR Shoemaker spacecraft's controlled landing on the surface of Eros. Joseph Veverka, imaging team leader and professor of astronomy at Cornell University, is lead author of a paper titled, "The landing of the NEAR-Shoemaker spacecraft on asteroid 433 Eros," and Mark Robinson of Northwestern University and co-authors report on "The nature of ponded deposits on Eros."

Before landing, NEAR Shoemaker had orbited Eros for a year, taking thousands of high-resolution ../../../images of the 21-mile-long asteroid. From the global map of the surface the team assembled, Thomas and his colleagues counted 6,760 rocks larger than about 16 yards across (15 meters) strewn over the asteroid's 434 square miles (1,125 square kilometers). They found that nearly half of these rocks were inside the crater, positioned near one end of the potato-shaped asteroid.

One of the big surprises from the maps is that Eros' surface appears to have a global cover of "loose fragmental debris." The surface appears to be blanketed with a fine material, some of which has created flat deposits, particularly in depressions, such as craters. These fine deposits appear to have been sorted from the upper portion of the asteroid's regolith, or soil. These so-called "ponded" deposits were visible in the final ../../../images NEAR Shoemaker transmitted before it touched down. In fact, as Veverka reports in his paper, "A strong argument is that the last image shows that the spacecraft landed on or within a few meters of a pond, a landform known to occur predominantly on the floors of craters."

The big question for researchers is: Do these observations of the surface mechanics of Eros indicate that similar processes are under way on other astronomical bodies? It is difficult to make comparisons because no other such distant body has been so closely mapped.

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