Douglas Isbell
Headquarters, Washington, DC             January 29, 1997
(Phone: 202/358-1753)

Diane Ainsworth
Jet Propulsion Laboratory, Pasadena, CA
(Phone: 818/354-5011)


RELEASE: 97-20

PLANETARY ASTRONOMERS START YEAR WITH TWO DISCOVERIES 

    Two newly detected members of the Solar System -- a rare 
asteroid orbiting close to Earth and a distant comet making its 
only appearance -- mark the first discoveries of the year for a 
team of astronomers at NASA's Jet Propulsion Laboratory (JPL), 
Pasadena, CA. 

    The discoveries, reported Jan. 10 by JPL planetary scientists 
Eleanor Helin, Steve Pravdo, David Rabinowitz and Ken Lawrence, 
were made possible with a few nights of clear observing weather 
and use of a sensitive, charge-coupled device (CCD) camera called 
the Near-Earth Asteroid Tracking (NEAT) system at Mt. Haleakala, 
Maui, HI. Since their initial sightings, both objects have become 
the focus of worldwide observations by astronomers in Japan, 
China, Australia, Canada, Italy and the Czech Republic.

    "This asteroid is a member of a rare class of asteroids, 
called Atens, which stay within Earth's orbit most of their 
lifetimes," said Helin, principal investigator of the NEAT 
project. "The object has a higher inclination to the plane of 
Earth's orbit than most Atens; in fact, at 31 degrees, it has the 
second highest inclination of all the Atens we've discovered." 

    The highly inclined orbit, which is unusual, may result from 
long-range interactions with the planets, or may be the outcome of 
previous orbits passing near the Earth. With the discovery of more 
Atens, the relative importance of these competing influences may 
be better understood.

    Dubbed 1997 AC11, the asteroid is a faint object with an 
absolute magnitude of 21, and probably measures about 600 feet in 
diameter.  It is only the 24th Aten to be discovered in 21 years, 
since Helin found and named the first Aten in January 1976.  With 
orbits that are smaller than Earth's, and short periods, Atens are 
in the vicinity of Earth frequently.  This closeness to Earth 
makes them more likely to impact the planet than other types of 
asteroids. 

    "Atens never wander far from the orbit of Earth and can cross 
Earth's orbit as many as four times a year," Helin said.  "1997 
AC11, for instance, has a period of 8/10ths of a year, or roughly 
9.5 months.  As we continue to observe it in coming months, we 
will be able to characterize its orbital path with more precision. 
With more precise data, we will be able to examine its potential 
for collision with Earth at some time in the future."

    Along with the newest Aten, astronomers also discovered a new 
comet, still distant but moving toward the Earth and Sun, as it 
passed through the constellation of Leo. Designated  Comet 1997 
A1, the celestial snowball is expected to make its closest 
approach to Earth on Feb. 6, passing at a distance of about 230 
million miles, but remaining visible in the night sky for several 
months thereafter.

    "This comet has traveled a long distance, originating in the 
Oort Cloud, a region far beyond Pluto's orbit which is believed to 
house trillions of incipient comets," Helin said.  "It has a 
parabolic orbit, which means it will travel through our Solar 
System once and probably never be seen again. Parabolic comets do 
not present their calling cards before arriving in the inner Solar 
System.  They appear without warning."

    At discovery, 1997 A1 was fairly dim at magnitude 19, and 
showed a weakly condensed nucleus with a diffuse halo and short 
tail, Helin said. The Minor Planet Center at the Smithsonian 
Astrophysical Observatory in Cambridge, MA, announced the 
discovery, reporting it as a parabolic comet, with an orbital 
inclination of 145 degrees from the ecliptic plane, and indicated 
that it would not pass any closer than 3.17 astronomical units 
(295 million miles) from the Sun. 

    JPL's NEAT team, in conjunction with another observing effort 
under way at the Laboratory's Table Mountain Observatory in San 
Bernardino, CA, will continue to track and characterize the comet 
over the next several months until it is no longer visible. 

    During its closest approach on Feb. 6, the newly discovered 
comet will be visible in the constellation of Cancer and brighten 
to a magnitude of about 18. Moderate-sized telescopes with CCD 
chips will be able to observe the comet, Helin said.  Astronomers 
report that the comet is continuing to outgas, or warm up and boil 
off some of its ices, as it moves toward the Sun.

    Low-resolution black-and-white images of both objects are 
posted on the Internet at the following URL:

           http://huey.jpl.nasa.gov/~spravdo/neat.html

    Discoveries of very faint or distant objects, and those 
surprisingly close by, are increasing due to the introduction of 
technologically advanced, fully autonomous CCD telescopes. The 
NEAT camera, for example, employs a very large, very sensitive 
4,096-by-4,096-pixel CCD. The camera is installed on a 39-inch 
telescope operated at the summit of Mt. Haleakala by the U.S. Air 
Force. 

    Using this powerful, fully automated system, astronomers are 
discovering many more objects than was possible in the past. The 
January observing run, for instance, produced more than 700 
asteroid sightings, including high-inclination inner-belt 
asteroids and a number of potential Mars-crossers, which will be 
confirmed after more observations become available. Total 
detections since NEAT began operations in late 1995 have climbed 
to more than 9,000 objects, of which more than 50 percent are new 
objects and more than 800 of those have received new designations.

    NEAT was built and is being managed by the Jet Propulsion 
Laboratory for NASA's Office of Space Science, Washington, DC. 

                             -end-