Nor is Eros the only asteroid that
gives evidence by variations of brilliancy that there is something
abnormal in its constitution; several others present the same
phenomenon in varying degrees. Even Vesta was regarded by Olbers as
sufficiently variable in its light to warrant the conclusion that it
was an angular mass instead of a globe. Some of the smaller ones show
very notable variations, and all in short periods, of three or four
hours, suggesting that in turning about one of their axes they present
a surface of variable extent toward the sun and the earth.
The theory which some have preferred -- that the variability of light
is due to the differences of reflective power on different parts of
the surface -- would, if accepted, be hardly less suggestive of the
origin of these little bodies by the breaking up of a larger one,
because the most natural explanation of such differences would seem to
be that they arose from variations in the roughness or smoothness of
the reflecting surface, which would be characteristic of fragmentary
bodies. In the case of a large planet alternating expanses of land and
water, or of vegetation and desert, would produce a notable variation
in the amount of reflection, but on bodies of the size of the
asteroids neither water nor vegetation could exist, and an atmosphere
would be equally impossible.
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