[meteorite-list] Corkscrew Asteroid (2003 YN107)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sat Jun 10 12:39:56 2006
Message-ID: <200606092035.NAA20954_at_zagami.jpl.nasa.gov>

http://science.nasa.gov/headlines/y2006/09jun_moonlets.htm

Corkscrew Asteroid
NASA Science News
June 9, 2006

A tiny asteroid looping around Earth for the past seven years is about
to leave the neighborhood.


June 9, 2006: News flash: Earth has a "second moon." Asteroid 2003 YN107
is looping around our planet once a year. Measuring only 20 meters
across, the asteroid is too small to see with the unaided eye???but it is
there.

This news, believe it or not, is seven years old.

"2003 YN107 arrived in 1999," says Paul Chodas of NASA's Near Earth Object
Program at JPL, "and it's been corkscrewing around Earth ever since."
Because the asteroid is so small and poses no threat, it has attracted
little public attention. But Chodas and other experts have been
monitoring it. "It's a very curious object," he says.

Most near-Earth asteroids, when they approach Earth, simply fly by. They
come and they go, occasionally making news around the date of closest
approach. 2003 YN107 is different: It came and it stayed.

"We believe 2003 YN107 is one of a whole population of near-Earth
asteroids that don't just fly by Earth. They pause and corkscrew in our
vicinity for years before moving along."

These asteroids are called Earth Coorbital Asteroids or "coorbitals" for
short. Essentially, they share Earth's orbit, going around the Sun in
almost exactly one year. Occasionally a coorbital catches up to Earth
from behind, or vice versa, and the dance begins: The asteroid, while
still orbiting the sun, slowly corkscrews around our planet.

"These asteroids are not truly captured by Earth's gravity," notes
Chodas. "But from our point of view, it looks like we have a new moon."

Astronomers know of at least four small asteroids that can do this
trick: 2003 YN107, 2002 AA29, 2004 GU9 and 2001 GO2. "There may be
more," says Chodas. He believes the list will grow as asteroid surveys
improve in sky coverage and sensitivity.

At the moment, only two coorbitals are actually nearby: 2003 YN107 and
2004 GU9. The others are scattered around Earth's orbit.

2004 GU9 is perhaps the most interesting. It measures about 200 meters
across, relatively large. And according to calculations just published
in the Monthly Notices of the Royal Astronomical Society (S. Mikkola et
al., 2006) it has been looping around Earth for 500 years--and may
continue looping for another 500. It's in a remarkably stable "orbit."

Right now, however, researchers are paying more attention to 2003 YN107
for one simple reason: it's about to depart. The asteroid's corkscrew
path is lopsided and on June 10th it will dip within 3.4 million km of
Earth, slightly closer than usual. Earth's gravity will then give the
asteroid the nudge it needs to leave.

"This is a chance to observe one of these asteroids [on the way out],"
explains Chodas.

It won't be gone forever. In about 60 years 2003 YN107 will lap Earth
again, resuming its role as a temporary, corkscrewing moonlet. In due
course, other coorbitals will do the same.

Each encounter is an opportunity for study--and possibly profit. Even
the most powerful telescopes cannot see much of these tiny asteroids;
they're just specks in the eyepiece. But one day, when the space program
is more advanced (see the Vision for Space Exploration), it
might be possible to visit, explore the moonlets and tap their
resources. "For now, they're just a curiosity," says Chodas.

News flash: Earth is about to lose a moon. More to come.
Received on Fri 09 Jun 2006 04:35:43 PM PDT