[meteorite-list] Recently Discovered Asteroid Could Hit Mars in January (2007 WD5)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 21 Dec 2007 13:04:29 -0800 (PST)
Message-ID: <200712212104.NAA18430_at_zagami.jpl.nasa.gov>

http://neo.jpl.nasa.gov/news/news151.html

Recently Discovered Asteroid Could Hit Mars in January
Steve Chesley and Paul Chodas
NASA/JPL Near-Earth Object Program Office
December 21, 2007

A recently discovered asteroid which passed close to the Earth in
November, is now headed towards a very close passage by Mars in late
January, and there is a small chance that it could hit that planet. The
probability of a collision is only 1 chance in 75, but
scientists are excited about the possibility. If it happens, the impact
would occur on January 30, 2008 at around 10:55 UT (2:55 a.m. PST).

[Graphic]
The current position of asteroid 2007 WD5, with its orbit shown in blue.
The asteroid's orbit stretches from just outside the Earth's orbit at
its closest point to the Sun, to the outer reaches of the asteroid belt
at its farthest. Uncertainty region at closest approach to Mars

[Graphic]
Uncertainty Region for 2007 WD5 at encounter with Mars, shown as white
dots. The thin white line is the orbit of Mars. The blue line traces the
motion of the center of the uncertainty region, which is the most likely
position of the asteroid.

In the likely event that the asteroid misses Mars, it could come back to
the vicinity of the Earth years or decades later, but our routine hazard
monitoring shows that there is no threat of an impact with the Earth.

[Animation]
Animation showing the motion of the uncertainty region of 2007 WD5 as it
approaches Mars.The thin white line is the orbit of Mars. The blue line
traces the motion of the center of the uncertainty region, which is the
most likely position of the asteroid.

Designated 2007 WD5, the asteroid was discovered on Nov. 20, 2007 by the
NASA-funded Catalina Sky Survey using a 1.5m telescope on Mt. Lemmon,
near Tucson. The object had already passed within 7.5 million km (5
million miles) of the Earth on Nov. 1, before it was discovered. Based
on its magnitude, we estimate the asteroid to be about 50 meters (160
feet) across. As the accompanying diagram shows, it has already reached
the halfway point between Earth and Mars. When it closes in on Mars, it
will approach from the day side, and would then be very difficult to
observe from any of the spacecraft on or around Mars. Our current best
estimate predicts the asteroid will miss Mars by 50,000 km, but the miss
distance is highly uncertain because the asteroid's path is not known
with sufficient accuracy. The uncertainty region during the Mars
encounter currently extends over a million kilometers (700,000 miles)
along a very slender ellipsoid only 1200 km (700 miles) wide, but the
ellipsoid does intersect Mars. The zone of potential impact on the
surface of Mars is approximately 800 km wide, and sweeps across the
Martian equator from southwest to northeast, crossing the equator at
roughly 30 deg W longitude. The MER Opportunity rover is close to the
southern edge of this possible impact zone but clearly outside it.

The asteroid is becoming increasingly difficult to observe, since it is
receding from the Earth and the waxing Moon is approaching the same part
of the sky. But it should become observable again early in January.
These new measurements will lead to a significant improvement in the
orbit accuracy, and we will then be able to refine the probability that
the asteroid might collide with Mars.

If the asteroid is indeed on a collision course, it would hit Mars with
a velocity of about 13.5 km/s (8.4 miles per second), and would produce
an explosion equivalent to about 3 MT of TNT. We can only speculate as
to the effects of such an impact, but it would be reasonable to expect a
crater nearly a kilometer across and a significant amount of dust lifted
into the atmosphere.

An impact would not be unprecedented: 21 fragments of Comet
Shoemaker-Levy 9 impacted Jupiter in July, 1994. Those impacts were
predicted with near certainty almost a year before the impact. But, with
a 1-in-75 chance, this asteroid's possible impact with Mars is far from
certain.
Received on Fri 21 Dec 2007 04:04:29 PM PST