Arecibo Radar Discovers Triple Near-Earth Asteroid
Image credit: Michael Nolan, Arecibo Observatory.
These radar images of near-Earth asteroid 2001 SN263 were
obtained on 2008 Feb 12 and 13. The resolution is 75m (250 feet)
per pixel. Because the moons are rotating more slowly than the
larger "primary", they appear narrower to the radar, which
measures distance and speed. Arecibo transmitted 500 000 Watts
toward the asteroid, but the echo power received with Arecibo's
ultra-sensitive detectors and processed into these images totals
less than a billionth of a billionth of a billionth of a
watt. Arecibo is both the world's most powerful radar
transmitter and the world's most sensitive radio receiver.
This experiment produced 75-meter-resolution images of a 2-km asteroid
when it was about 11,000,000 km away.
This is like using a camera in New York to image a person in Los
Angeles with one-inch resolution.
More versions of image
Image from Feb 12
Image from Feb 13 the same size as Feb 12
Image from Feb 13
Image from Feb 14
Feb 12, 13, 14, 18.
Cornell Press release
Arecibo finds first near-Earth triple asteroid
FOR RELEASE: Feb. 13, 2008
Contact: Blaine Friedlander
Phone: (607) 254-8093
Cell: (607) 351-2610
bpf2@cornell.edu
PHOTO AVAILABLE
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.
For more news at Cornell, go to http://pressoffice.cornell.edu/ <http://pressoffice.cornell.edu>
Image from Feb 13 the same size as Feb 12
Image from Feb 12
Image from Feb 13
Image from Feb 14