SCIENCE LAB SPECIAL : COSMIC INCUBATOR

 

IN the moons of Mars, a tale of an asteroid's violent death. Something's not quite right about the moons of Mars.

They are too small - Phobos is 17 miles across [ 27 kilometers across ], and Deimos is nine miles in length. And they aren't round, but lumpy, misshapen objects.

Frankly, they don't resemble moons at all. '' They look like asteroids, they smell like asteroids, as well as looking like potatoes,'' said James O' Donoghue, a planetary astronomer in England. Perhaps, then, astronomers have suggested, they are asteroids - two space rocks captured long ago by Mars gravity.

A new study makes a case that the moons indeed have an asteroid origin. But they don't appear to have been captured whole.

Using computer-powered simulations, scientists describe a situation in which an asteroid was captured by Mars and torn apart by the planet's gravity, forming a debris cloud, and maybe a ring system, around Mars that ultimately clumped together to form two moons.

'' What they've got here is really compelling,'' said Dr. Donoghue, who wasn't involved with the study. '' I'm sold.''

The notion that Phobos and Deimos may be captured asteroids has long up against one major problem:

Their orbits are too circular and too neatly aligned around Mar's equator. If these moons were once asteroids, their orbits would be expected to be tilted and perhaps oval shaped.

That they aren't supports the theory that they were forged another way. [ Robin George Andrews ]