If like a talented basketball player you had a strong vertical leap (say 36 inches, or just under 1 meter) you could jump a mile (1.6 kilometers) high on Asteroid 433 Eros. But be careful, because you might also launch yourself into orbit around the distant space rock.

But if you keep your footing, you'd have a clear view of a strange and surprising world with house-sized boulders, inexplicable smooth spots and very near horizons that in some directions loom like mountains on Earth -- all on a fairly firm but incredibly uneven and rocky surface coated with a thin layer of dust.

If, by chance, you were also an asteroid expert, you'd be very surprised at the lack of small impact craters on the otherwise heavily scarred, vaguely shoe-shaped asteroid.

Eons of impacts have created at least 100,000 craters on Eros, which is about 21 miles (33 kilometers) long, 8 miles (13 kilometers) wide and 8 miles thick.

But one puzzle revealed by the new study is a paucity of small impact craters -- fewer in a given amount of surface area than are observed on the Moon, Thomas said.

The lack of tiny divots is not due to a shortage of things to run into -- the "Asteroid Belt" between Mars and Jupiter where Eros roams is loaded with millions of smaller rocks prone to taking pot shots at each other.

Something must be covering up or eroding small craters, researchers say. One possible explanation is a phenomenon called seismic shaking. It goes like this:

When another space rock slams into Eros, it sends shock waves, or sound waves, reverberating through the asteroid, Thomas explains. This seismic shaking causes small crater walls to crumble and settle, much like a mound of flour in a bowl would level out upon shaking.

On an asteroid, seismic shaking would be enhanced by the low gravity, which would allow small rocks and other debris to move around more freely than on a more massive object like the Moon.

Larger craters would not be affected as significantly by seismic shaking.

But this shaking, or some other process, might also have created another curious feature: smooth, flat areas at the bottom of several craters, large and small. The flat spots, ranging from about 1 to 16 yards (1 to 15 meters) across, appear to be made of the same material as the crater walls within which they sit. This would rule out a process known to create similar flat features on the Moon, when an impact carves out surface soil, exposing different and often more solid material below.