Douglas Isbell
Headquarters, Washington, DC August 22, 1996
(Phone: 202/358-1753)
Jane Platt
Jet Propulsion Laboratory, Pasadena, CA
(Phone: 818/354-5011)
RELEASE: 96-172
NEW OBJECT MOVES LIKE A COMET BUT LOOKS LIKE AN ASTEROID
Scientists at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA, 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 PW 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 five to ten miles, appears to be an asteroid, a chunk of rock that orbits the Sun, Helin said. However, unlike most typical asteroids, which inhabit orbits no further out than the planet 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 normally expected comet-like activity such as a dust coma have 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 a crust of non-volatile materials.
This puzzling object was discovered through a combination of high-tech telescopes, sophisticated computer 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 other 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, MA, 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.
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.
NEAT was built and is managed by JPL for NASA's Office of Space Science, Washington, DC.
The electronic image that led to the discovery of 1996 PW is available on the NEAT program's Internet home page at:
September 6, 1996
Web posted at: 9:15 a.m. EDT
LOS ANGELES (AP) - Astronomers are baffled by a strange object that moves like a comet but looks like an asteroid.
Astronomers spotted the object in space using an Air Force telescope equipped a special camera.
The object, with a diameter of 5 to 10 miles, may be an unusual asteroid or a dead comet stripped of all volatile material, NASA officials said Wednesday.
"This is a misfit in the grand scheme of things," Eleanor Helin, principal investigator of the Near-Earth Asteroid Tracking program at NASA's Jet Propulsion Laboratory, said in a statement. Scientists said nothing like it has been seen before.
The object, dubbed 1996 PW, was spotted in data taken from an August 9 observation atop Mount Haleakala on Maui, Hawaii. A special camera attached to the telescope automatically surveys the skies for objects-asteroids and comets-which could pose a hazard to Earth.
Asteroids are rocky bodies that mainly orbit in the "asteroid belt" between Jupiter and Mars. Comets generally have orbits that go beyond the planets and have volatile material streaming off.
No comet-like gas emissions were observed from 1996 PW, even during its closest approach to the sun, supporting the argument that the object is an asteroid.
However, its orbit-an elongated, comet-like circuit that stretches into the void beyond the orbits of Neptune and Pluto-is estimated to have a period of 5,000 years.
The orbits of the majority of asteroids are on the order of three to five years, and in an extreme case, 50 years, said Steve Pravdo, project task manager for the asteroid tracking program.
The comet-like motion was spotted by scientist Gareth Williams while processing the data with a computer at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts.
Scientists using a 5-meter telescope at Palomar Mountain in San Diego County plan on making observations to determine the object's physical measurements and composition.
The Jet Propulsion Laboratory's special camera, installed on Maui in December 1995, uses time exposures to spot the movement of objects near Earth among the thousands of celestial bodies in every image.
But there's no reason to worry about 1996 PW hitting Earth, Pravdo said.
It's in a "dumb orbit," he said. "It's on its way out."
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