Scientists at NASA's Jet Propulsion Laboratory (JPL) have discovered a unique object, designated 1996PW, that may be either an unusual asteroid or an extinct comet. 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.

Eleanor Helin, a planetary astronomer at JPL and the NEAT Principal Investigator calls the object "a misfit in the grand scheme of things." 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, 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. JPL research scientist Dr. Michael Keesey estimates its period at about 5000 years.

Although 1996 PW is in an comet-like orbit, 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. 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.

1996PW object was discovered through a combination of high-tech telescopes, sophisticated computer software and human detective work. The NEAT program at Haleakala 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. 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 electronic image that led to the discovery of 1996PW is available on the NEAT program's Internet home page at: http://huey.jpl.nasa.gov/~spravdo/neat.html