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No. 135: MAY-JUN 2001

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Asteroid Ponds, Beaches, And Boulders

Once considered only dull, nondescript vagabonds of the solar system, asteroids are turning out to be rather mysterious and surprisingly complex bits of celestial real estate. The close-up photos of the asteroid Eros (35-kilometers long) from the spacecraft NEAR-Shoemaker have added two new phenomena to the list of asteroid enigmas.

Boulders. Eros is covered with huge boulders -- perhaps a million of them over 8-meters wide. The boulders are likely just accreted solar-system debris; but why are they strewn naked on the surface of Eros instead of being intermixed with other rocky debris? Speculation is that the large boulders were coaxed to the surface preferentially over the eons by seismic vibrations -- said vibrations being caused by multitudinous impacts. This type of jostling action also explains why Brazil nuts greet you when you open a well-travelled can of mixed nuts!

Ponds and beaches. The fine debris coating Eros may also have responded to the same vibrations, but in different ways. It sort of "flowed" downhill to form curious flat features resembling ponds. Between the ponds and rough terrain, the fine debris has also built up transition zones that look like beaches. Cormell's J. Veverka isn't betting on any of the proposed theories as yet. He declared:

We're facing processes we're not familiar with. I truly don't know what's going on.

(Kerr, Richard A.; "Strange Doings on a NEAR-Struck Asteroid," Science, 291: 1467, 2001.)

Comment. It is interesting to observe how vibrations may emulate the action of water in creating sandy topography. As a terrestrial case in point, the famed Mima Mounds in Washington state may have been created not by flowing water or pocket gophers but by earthquake vibrations. (SF#91 and SF#108)

From Science Frontiers #135, MAY-JUN 2001. � 2001 William R. Corliss

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