[meteorite-list] LONEOS Discovers Asteroid with the Smallest Orbit (2004 JG6)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu May 20 20:01:23 2004
Message-ID: <200405210001.RAA20522_at_zagami.jpl.nasa.gov>

http://www.lowell.edu/press_room/releases/recent_releases/2004JG6_rls.html

Lowell Observatory
For Immediate Release

May 20, 2004

contact: Steele Wotkyns
(928) 233-3232
steele_at_lowell.edu

LONEOS Discovers Asteroid with the Smallest Orbit

Flagstaff, AZ-The ongoing search for near-Earth asteroids at Lowell
Observatory has yielded another interesting object. Designated 2004 JG6,
this asteroid was found in the course of LONEOS (the Lowell Observatory
Near-Earth Object Search) on the evening of May 10 by observer Brian Skiff.

"I immediately noticed the unusual motion," said Skiff, "so it was certain
that it was of more than ordinary interest." He quickly reported it to the
Minor Planet Center (MPC) in Cambridge MA, which acts as an international
clearinghouse for asteroid and comet discoveries. The MPC then posted it on
a Web page for verification by astronomers worldwide. It happened that all
the initial follow up observations, however, were obtained by amateur and
professional observers in the Southwest US. The additional sky positions
measured in the ensuing few days allowed an orbit to be calculated.

The official discovery announcement and preliminary orbit were published by
the MPC on May 13. This showed that the object was located between Earth and
Venus (presently the very bright "evening star" in the western sky). In
addition, 2004 JG6 goes around the Sun in just six months, making it the
asteroid with the shortest known orbital period. Ordinary asteroids are
located between the orbits of Mars and Jupiter, roughly two to four times
farther from the Sun than Earth, taking several years to go around the Sun.

Instead, 2004 JG6 orbits entirely within Earth's orbit, only the second
object so far found to do so. "What makes this asteroid unique is that, on
average, it is the second closest solar system object orbiting the Sun,"
said Edward Bowell, LONEOS Director. Only planet Mercury orbits closer to
the Sun.

As shown in the included diagram, JG6 crosses the orbits of Venus and
Mercury, passing less than 30 million miles from the Sun every six months.
The approximate average orbital speed of this asteroid is more than 30
km/sec, or 67,000 miles per hour. Depending on their locations, the asteroid
may pass as close as 3.5 million miles from Earth and about 2 million miles
from planet Mercury. In the coming weeks 2004 JG6 will pass between Earth
and the Sun, just inside Earth's orbit. It will move through the
constellations Cancer and Canis Minor low in the western sky at dusk.
Because of the near-exact six-month period, the asteroid should be
observable again in nearly the same spot in the sky next May, having gone
around the Sun twice while Earth will have made only one circuit.

>From present estimates, 2004 JG6 is probably between 500 meters and 1 km in
diameter. Despite its proximity, the object poses no danger of colliding
with Earth.

Asteroids with orbits entirely within the Earth's orbit have been informally
called "Apoheles," from the Hawaiian word for orbit. Apohele also has Greek
roots: "apo" for outside, and "heli" for Sun. Objects orbiting entirely
within Earth's orbit are thought by dynamicist William F. Bottke of
Southwest Research Institute and colleagues to comprise just two percent of
the total near-Earth object population, making them rare as well as
difficult to discover. This is because they stay in the daylight sky almost
all of the time. There may exist about 50 Apoheles of comparable size to or
larger than 2004 JG6, but many of them are certain to be unobservable from
the ground.

The first asteroid found entirely inside Earth's orbit was 2003 CP20, found
just over a year ago by the NASA-funded Lincoln Laboratory Near-Earth
Asteroid Research project, which observes near Socorro, New Mexico. Although
larger than 2004 JG6, 2003 CP20 is a little more distant from the Sun.

LONEOS is one of five programs funded by NASA to search for asteroids and
comets that may approach our planet closely. The NASA program's current goal
is to discover 90 percent of near-Earth asteroids larger than 1 km in
diameter by 2008. There are thought to be about 1,100 such asteroids.

#END#

For additional information:

LONEOS = http://asteroid.lowell.edu/asteroid/loneos/loneos_disc.html
MPC = http://cfa-www.harvard.edu/iau/mpc.html
MPC's official discovery announcement:
http://cfa-www.harvard.edu/mpec/K04/K04J60.html
JPL orbit diagram/animations:
http://neo.jpl.nasa.gov/cgi-bin/db_shm?sstr=2004+JG6 (for best results, copy
and paste URL into browser)
Static view of 2004 JG6 by Tom Polakis :
http://www.psiaz.com/polakis/misc/2004JG6.jpg

Diagram of 2004 JG6 by Larry Wasserman, Astronomer, Lowell Observatory (a
pdf)
Received on Thu 20 May 2004 08:01:11 PM PDT