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Mathilde - part 2 of 2

Astronomy, February 1999, p. 59: The Connection with Meteorites

Scientists hope NEAR’s close look at Mathilde and Eros will solve one of
the biggest mysteries of asteroid and meteorite study: To what asteroid
class do meteorites belong? Scientists think that nearly all meteorites
were once parts of asteroids, and collisions broke off pieces and
changed their orbits to ones intercepting Earth.
Although the S and C classifications make up almost 75 percent of all
known asteroids, the spectrum of neither type corresponds very closely
to most meteorites found on Earth. ln fact, only a handful of asteroids
fit precisely the spectral class of 90 percent of all known meteorites.
Even more puzzling, the closer you get to Earth, the worse the match. C
asteroids, orbiting from the middle of the asteroid belt outward, match
only poorly. S asteroids, orbiting from the middle of the asteroid belt
inward, match not at all. While almost all near-Earth asteroids belong
to the S class, only 10 percent of meteorites found on Earth resemble
these asteroids even vaguely.
In many ways the study of asteroids today is comparable to the study of
the major planets in 1968. Before the first orbital missions to Mars and
Venus, most of our knowledge of the planets was based on their
telescopic appearance and spectra. Our only good views had been limited
to a few quick flybys, mere glimpses by a handful of spacecraft. Overall
we knew little and understood less.
Similarly, other than the tantalizing glimpses provided by the NEAR and
Galileo spacecraft, we have not yet seen an asteroid in detail.
Astronomers have approximated the make-up and shape of these mysterious
objects, but without actually looking at them close up, we can't really
know what they are. This should all change in 1999, as NEAR slips into
orbit around Eros and begins to pick at its mysteries. (Robert
Zimmermann).



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