[meteorite-list] Long-lost, Dangerous Asteroid Is Found Again (6344 P-L)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 15 Oct 2007 11:59:46 -0700 (PDT)
Message-ID: <200710151859.LAA07195_at_zagami.jpl.nasa.gov>

http://www.sciencedaily.com/releases/2007/10/071011213216.htm

Long-lost, Dangerous Asteroid Is Found Again
Science Daily
October 15, 2007

Echoing the re-discovery
of America by the Spanish long after an earlier Viking reconnaissance,
astronomers have learned that a recently observed asteroid - one that
could potentially hit the Earth - was actually first observed nearly a
half-century ago. Researchers at the Minor Planet Center of the
Smithsonian Astrophysical Observatory in Cambridge, MA have confirmed
work by SETI Institute astronomer Peter Jenniskens that the recently
discovered asteroid 2007 RR9 is in fact the long-lost object 6344 P-L.

6344 P-L was last seen in 1960, and ever since has had the peculiar
distinction of being the only Potentially Hazardous Asteroid without a
formal designation. "The object was long recognized to be dangerous, but
we didn't know where it was," says Jenniskens. "Now it is no longer just
out there."

A designation as Potentially Hazardous means that 2007 RR9 is one of 886
(not 887) known asteroids bigger than 150 m (500 ft) in diameter that
come to within 0.05 astronomical units of Earth's orbit (roughly
7,480,000 km or 4,650,000 miles). The size is estimated on the basis of
the object's observed brightness and an assumed reflectance of 13 percent.

Jenniskens believes that this object may not, in fact, be an asteroid.
"This is a now-dormant comet nucleus, a fragment of a bigger object
that, after breaking up in the not-so-distant past, may have caused the
gamma Piscid shower of slow meteors (IAU #236) that is active in
mid-October and early November," he says. 2007 RR9 moves in a 4.70-year
orbit, nearly all the way out to the distance of Jupiter. Because of
this elongated orbit, it has a Tisserand parameter of T = 2.94, which
defines it dynamically as a Jupiter Family Comet (T = 2.0 - 3.0), not an
asteroid (T > 3.0).

So far, this object has not yet been seen to be even weakly active, but
the now dormant comet is still moving closer to the Sun. It is sliding
rapidly toward visibility in the southern hemisphere, and is expected to
brighten to magnitude +18.5 in mid-October. According to Gareth V.
Williams of the Minor Planet Center, it will pass Earth around November
6 at 0.07 AU, when the minor planet is at high latitudes in southern skies.

The original designation of P-L stands for "Palomar-Leiden," the
juxtaposition of two observatory names that reflect what was a very
fruitful collaboration by the trio of pioneer asteroid searchers Tom
Gehrels of the University of Arizona, and Ingrid van Houten-Groeneveld
and her husband Cornelis Johannes van Houten. Gehrels made a sky survey
using the 48-inch Schmidt Telescope at the famed Palomar Observatory,
long before modern asteroid reconnaisances, and shipped the photographic
plates to the van Houtens at Leiden Observatory in the Netherlands.
There, Ingrid discovered 6344 P-L on four plates taken on September
24-28, 1960. The trio are jointly credited with several thousand
asteroid discoveries, but only 6344 P-L is a potential danger to Earth.

Peter Jenniskens is a meteor astronomer with the SETI Institute and
author of "Meteor Showers and their Parent Comets" published by
Cambridge University Press (2006). He is also credited with the
identification of the parent body of the Quadrantid meteor shower. As it
happens, he graduated from Leiden Observatory in 1992, before joining
the SETI Institute.

Note: This story has been adapted from material provided by SETI Institute.
Received on Mon 15 Oct 2007 02:59:46 PM PDT