[meteorite-list] Asteroid Color Clans

From: Bernd Pauli HD <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 10:06:13 2004
Message-ID: <3DC5A49B.FCD9CF39_at_lehrer.uni-karlsruhe.de>

Asteroid Color Clans (J. Kelly Beatty)

Although spacecraft views give the impression that asteroids are
bland, gray hunks of rock, astronomers have known for decades
that they exhibit slight color differences. In fact, these subtle hues,
together with surface reflectivity, form the basis for the dozen or
so major classifications. For example, bodies in the inner asteroid
belt (dominated by S types) are in general slightly redder than their
darker and more neutral-colored siblings (the C types) farther out.

Colors should also be the same within an asteroid "family," which
results from the collisional shattering of a large precursor. To date
astronomers have distinguished some thirty families based on the
clustering of orbital characteristics such as semimajor axis (mean
distance from the Sun) and inclination. And while previous studies
have indeed established color similarities among the most populous
families, those efforts will soon be eclipsed by a vast new survey
to be published in the Astronomical Journal.

The new work draws upon the Sloan Digital Sky Survey, the huge ongoing
endeavor to map the positions, brightnesses, and colors of some 500
million stars and galaxies in five color bands, from ultraviolet through
near infrared (S& T August 1997, page 40). Sloan's dedicated 2.5-meter
telescope also records asteroids by the tens of thousands, a scientific
bonus that has been exploited by Zeljko Ivezic (Princeton University)
and eight colleagues.

Using a set of 6,612 asteroids for which proper (unperturbed) orbital
elements have been estimated, Ivezic's team found that asteroid families
can be easily distinguished by color. Thus the researchers believe their
color data provide a "dramatic independent confirmation" of the
families' reality. Even groups with hopelessly overlapping orbital
characteristics could be disentangled through color discrimination.
Moreover, Ivezic notes, a great many of the asteroids previously thought
to be uncommitted loners seem to show color kinship with the most
populous groupings. All told, his team concludes, "at least 90 percent
of asteroids are associated with families."

(Sky and Telescope, Nov. 2002, p. 20)
Received on Sun 03 Nov 2002 05:35:07 PM PST