Scientists at NASA's Jet Propulsion Laboratory (JPL), have discovered a unique and baffling object that may be either an unusual asteroid or an extinct comet.
The object, designated 1996 PW, was detected by astronomers using data from the Near-Earth Asteroid Tracking (NEAT) program that employs a JPL-developed camera mounted on a U.S. Air Force telescope atop Mt. Haleakala on Maui, Hawaii.
Puzzled scientists are still striving to understand exactly what object 1996 is and where it came from. "This is a misfit in the grand scheme of things," according to Eleanor Helin, a planetary astronomer at JPL and the NEAT principal investigator.
At first look, the object, which has a diameter of about 8 to 16 kilometers (about 5 to 10 miles), appears to be an asteroid, a chunk of rock that orbits the sun, said Helin. However, unlike most typical asteroids, which inhabit orbits no farther out than Jupiter, 1996 PW has a highly elongated, comet- like orbit that stretches into the vast outer reaches of the solar system, far beyond Neptune and Pluto. Its orbit has a period currently estimated at 5,000 years, according to JPL research scientist Dr. Michael Keesey.
Although 1996 PW is in an orbit resembling that of a long- period comet, no gaseous emissions or other comet-like activity, such as a dust come, has been observed, even during its current closest approach to the Sun, Helin said.
Helin and other astronomers studying the object believe that this raises the possibility that it was once an active comet, but is now inert, either because its ice and gases have been stripped away or because it is covered and insulated by non-volatile materials.
This puzzling object was discovered through a combination of high-tech telescopes, sophisticated software and human detective work. The NEAT program at Haleakala, carried out under the direction of Helin and task manager Dr. Steven Pravdo, also of JPL, is the world's first fully autonomous near-Earth object imaging system. It consists of a computer controller and a highly sensitive CCD camera sensor mounted on a telescope. The system is designed to discover and track asteroids and comets as they approach Earth from deep space.
The NEAT system is mounted on the U.S. Air Force's Ground- Based Electro-Optical Deep Space Surveillance System's one-meter telescope at the Maui facility.
Observational data from NEAT on the night of August 9 recorded the appearance of 1996 PW, along with similar observations of 150 more typical asteroids in the belt between Mars and Jupiter. More observations were made three nights later. While computer-processing the data at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts, Gareth Williams noticed the object had an unusual apparent motion.
Due to the current position in space of 1996 PW, scientists will have an excellent window of opportunity to study the object more thoroughly over the next six months.
Further observations were made at Haleakala by NEAT and by an Italian amateur astronomer, who learned of the object from the Minor Planet Center's World Wide Web site. JPL's David Rabinovitz provided positional and color information on the discovery. Vital operational work on the incoming data was handled by JPL's Ken Lawrence, with results reviewed by team members.
The NEAT camera was installed at the Air Force's Maui facility in December 1995 to conduct a systematic search for asteroids and comets that come near Earth. With its short exposure time and fast electronics, NEAT is able to achieve wide- sky coverage. It can also detect objects much fainter than was possible with the photographic Schmidt telescope at Palomar Observatory in Southern California, which Helin used to conduct asteroid searches for 20 years.
NEAT was built and is managed by JPL for NASA's Office of Space Science, Washington, D.C.
The electronic image that led to the discovery of 1996 PW is available on the NEAT Program's Internet Home Page at: http://huey.jpl.nasa.gov/~spravdo/neat.html
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