S-type asteroid
An S-type asteroid is a stony asteroid of moderate brightness, the kind that supplies most ordinary chondrites.
S-type asteroids are stony asteroids with spectra showing the minerals olivine and pyroxene. They reflect a moderate amount of sunlight, about 15 to 30 per cent, and are common in the inner part of the asteroid belt and among near-Earth asteroids. The S stands for stony, or silicaceous.
For decades, astronomers wondered why S-type spectra did not quite match the ordinary chondrites, the commonest meteorites. The answer turned out to be space weathering: the solar wind and micrometeorite impacts slowly redden and darken their surfaces. In 2010 Japan's Hayabusa mission settled the matter by returning grains from the S-type asteroid Itokawa that were clearly LL ordinary chondrite material.
Other S-type asteroids visited by spacecraft include Eros, Ida, Gaspra and the Didymos pair. Their families in the inner belt are thought to be the main suppliers of the H, L and LL chondrites that fall to Earth today.
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Level: Explorer Ages 10 and up