Two space rocks in our solar system's outer asteroid
belt might contain mineral evidence for a new class of asteroids or long
The asteroids, (7472) Kumakiri and (10537) 1991 RY16, were found to contain basalt, a grey-black mineral that forms much of the crust on Earth and the other inner planets.
Basalt has also been found in space rocks shed by
Vesta, the third largest object in the
belt, located between the orbits of
Jupiter and Mars. The presence of basalt is evidence that an object was once
large enough to sustain internal heating.
"We need now to observe both objects in the
near-infrared range to confirm whether they have a basaltic surface," said
study leader Rene Duffard of the Institute of Astrophysics of Andalusia in
Grenada, Spain. "If they do, we will need to try to work out where they came
from and the fate of their parent objects. If they do not, we will have to
come up with a new class of asteroid."
The finding, made using photometric data from the
Sloan Digital Sky Survey (SDSS), was presented at annual European Planetary
Science Congress in Potsdam, Germany.
Until recently, all basalt-containing asteroids were
thought to be fragments of
In 2001, scientists discovered (1459) Magnya, an object in the outer asteroid
belt that contained basalt of a slightly different chemical composition,
suggesting it did not belong to the Vesta
The lack of basalt and another mineral, olivine, in
asteroid belt objects has long puzzled scientists. These two minerals would
have formed the crust and mantle, respectively, of belt objects the size of
Vesta or larger; theory predicts that more than half of all
should be composed of one or the other of these
"Finding either one is significant because both are
quite rare, much rarer than they should be," said Michael Gaffey, a geologist
at the University of North Dakota who was not involved in the study. "Roughly
99 percent of the stuff we expect to see [in the asteroid belt] is
One possibility, Gaffey told SPACE.com, is that
the parent bodies of Kumakiri and 1991 RY16 were long ago worn down by
repeated collisions into smaller and smaller pieces, which have since been
whisked out of our solar system.