[meteorite-list] First Near-Earth Triple Asteroid Discovered by Arecibo Observatory Astronomers

[Ron Baalke]

Press Relations Office
Cornell University
Ithaca, New York

Media Contact: Blaine Friedlander
Phone: (607) 254-8093

FOR RELEASE: Feb. 13, 2008

First near-Earth triple asteroid discovered by Arecibo Observatory
astronomers -- a mere 7 million miles from Earth

ITHACA, N.Y. -- Once considered just your average single asteroid, 2001
SN263 has now been revealed as the first near-Earth triple asteroid ever
found. The asteroid -- with three bodies orbiting each other -- was
discovered this week by astronomers at the sensitive radar telescope at
Cornell University's Arecibo Observatory in Puerto Rico.

Cornell University and Arecibo astronomer Michael C. Nolan said he and his
colleagues made the discovery when they obtained radar images Feb. 11. The
group subsequently took more images to learn that the three objects -- about
7 million miles from Earth -- are rotating around each other.

The main, central body is spherical with a diameter of roughly 1.5 miles (2
kilometers), while the larger of the two moons is about half that size. The
smallest object is about 1,000 feet across, or about the size of the Arecibo
telescope.

Other triple asteroids exist in the asteroid belt (between Mars and Jupiter)
and beyond, but this is the first near-Earth system where the actual shapes
of objects can be clearly seen.

The Arecibo telescope is operated for the NSF by Cornell's National
Astronomy and Ionosphere Center.

"This discovery has extremely important implications for ideas about the
origins of near-Earth asteroids and the processes responsible for their
physical properties," said Nolan. "Double, or binary, asteroid systems are
known to be fairly common -- about one in six near-Earth asteroids is a
binary -- but this is the first near-Earth triple system to be discovered."

The object was first discovered visually Sept. 19, 2001, by the Lincoln Near
Earth Asteroid Research (LINEAR) project, part of the Massachusetts
Institute of Technology's Lincoln Laboratory. The orbits of binary -- and
now triple -- asteroid systems unveil the mass and allow astronomers to
assess whether they are stable over millennia or have formed very recently.
Previous radar investigations of binary near-Earth asteroids have disclosed
extraordinary physical and dynamical characteristics.

Nolan said this discovery prompts several important questions: Are the
objects orbiting in the same plane? How rapidly are the orbits changing with
time? Did the moons form when this asteroid formed in the main asteroid
belt, or after it arrived in near-Earth space?

Because of the small sizes and irregularly shaped components, 2001 SN263
should offer unique insights relative to the much larger triple systems in
the main asteroid belt, said Nolan. "Examining the orbits of the moons as we
continue to observe 2001 SN263 over the next few weeks may allow us to
determine the density of the asteroid and type of material from which it is
made," he said. "We will also be studying its shape, surface features and
regolith [blanketing material] properties."

Radar observations by the Arecibo Observatory can image a much larger
fraction of the population of near-Earth asteroids than spacecraft. For
example, Arecibo has discovered more than half of the near-Earth binary
asteroid systems discovered since 1999. Continued observations will
undoubtedly lead to the discovery of new classes of objects, such as this
triple system. While the Arecibo telescope is capable of these
investigations, the future of the radar program and the entire telescope are
in considerable doubt due to NSF budget cuts.

Nolan's collaborators on the project are Ellen S. Howell, Arecibo
Observatory/Cornell University; Lance A.M. Benner, Steven J. Ostro and Jon
D. Giorgini, Jet Propulsion Laboratory/California Institute of Technology;
Michael W. Busch, Caltech; Lynn M. Carter and Ross F. Anderson, Smithsonian
Institution; Chris Magri, University of Maine at Farmington; Donald B.
Campbell and Jean-Luc Margot, Cornell; Ronald J. Vervack Jr., Johns Hopkins
University Applied Physics Laboratory; and Michael K. Shepard, Bloomsburg
University.

IMAGE CAPTION:
[http://www.news.cornell.edu/stories/Feb08/asteroid.png (8KB)]
2001 SN263 has now been revealed as the first near-Earth triple asteroid
ever found. (Arecibo Observatory)