[meteorite-list] Asteroid Follows Earth Around Orbit (Asteroid 2002 AA29)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:07:03 2004
Message-ID: <200210231722.KAA07562_at_zagami.jpl.nasa.gov>

http://www.newscientist.com/news/news.jsp?id=ns99992953

Asteroid follows Earth around orbit
Will Knight
New Scientist
October 20, 2002

Astronomers have discovered a 100-metre asteroid that follows the Earth's
path around the Sun in a reversible "horseshoe" orbit. It is the first
object found to be closely following Earth's orbit, though other
"co-orbital" asteroids follow the planets Jupiter and Mars.

The object, 2002 AA29, also becomes a temporary second moon to the Earth
from time to time, with the next rendezvous expected in 2600. It was first
spotted on 9 January 2002 by the Lincoln Near Earth Asteroid Research
(LINEAR) automated sky survey project.

Detailed analysis of the asteroid's movement now shows that it follows the
Earth's orbit in a peculiar manner, first approaching the Earth from one
side then, 95 years later, sweeping around to the other side.

The asteroid will make its closest approach to the Earth in 2003, to about
12 times the distance from the Earth to the Moon. It will then move around
the Sun to approach from the opposite side in 2098.

"2002 AA29 introduces an important new class of objects offering potential
targets for space missions and clues to asteroid orbit transfer evolution."
writes Martin Connors, at Athabasca University in Canada, and his colleagues
in an article published in the journal Meteoritics and Planetary Science.

Parent planet

"This is the first body known to be in a simple heliocentric horseshoe
orbit, moving along its parent planet's orbit," they write. The strange
horseshoe-shaped orbit is the result of the complex interaction between the
gravitational attraction of the Sun and the Earth.

The new calculations also show that in 600 years time 2002 AA29 will
temporarily circle the Earth itself. For 50 years it will act like a second
moon, orbiting our planet once a year. But it will not be a genuine moon
because its orbit will still be controlled by the Sun.

Paul Wiegert of Queen's University, Ontario, Canada, says: "Both the Earth
and the asteroid still both go around the Sun, but the relative looping
motion of the asteroid in some ways resembles a satellite orbit, with an
apparent period of one year."

Another asteroid, 3753 Cruithne was found to move around the Earth in a
similar horseshoe orbit in 1997. But this object does not follow the same
line as the Earth around the Sun and so cannot be called co-orbital.
Received on Wed 23 Oct 2002 01:22:04 PM PDT