[meteorite-list] NASA's New Asteroid Sentry Stands Watch

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:02:28 2004
Message-ID: <200203141723.JAA20908_at_zagami.jpl.nasa.gov>

http://www.space.com/scienceastronomy/solarsystem/asteroid_sentry_020314.html
        
NASA's New Asteroid Sentry Stands Watch
By Robert Roy Britt
14 March 2002

NASA announced this week a new Web-based asteroid monitoring system,
called Sentry, to monitor and assess the threat of space rocks that
could possibly strike the Earth.

The setup is designed to help scientists better communicate with each
other about the discoveries of new, potentially threatening asteroids
and the follow-up observations that typically show those asteroids to
be, in fact, no threat.

While no large asteroid is currently known to be on a collision course
with our planet, experts say an eventual impact is inevitable and the
consequences could be grave, up to and including global devastation
that might destroy civilization as we know it. The odds of such an
impact in any given decade are extremely low, and most experts agree
that there would likely be at least 10 years of warning if such an
object were ever spotted.

Smaller asteroids, however, are more likely to hit Earth in any given
year and could cause significant local or regional damage. The odds are
low in any given year. But over the course of a generation, the chances
of such an event become significant.

The odds of a locally or regionally destructive asteroid hitting an
inhabited area in a given 50-year period are about 1-in-160, according
to experts.

False alarms

In recent years, asteroid experts around the globe have struggled to
develop a system to catalogue and track newly spotted Near Earth
Asteroids -- those that are close enough to Earth's orbit to warrant
scrutiny -- and to properly communicate any possible threats to the
public.

However, asteroids move so slowly against the background of stars that
when one is first discovered, astronomers cannot pin down its exact
path. Therefore, a wide range of possibilities are generated for the
rock's possible orbit around the Sun, and often Earth becomes a
possible target in those projected paths.

A handful of false alarms, in which scientists said there was a remote
threat that a particular asteroid would hit Earth in a certain year,
have made headlines and frightened the public. The first and most
notable was an asteroid called 1997 XF11, which briefly loomed as a
frightening nemesis until four years ago this week, when new
observations revealed it would miss the planet.

A similar but less publicized "threat" emerged last August with an
asteroid called 2001 PM10. Data on the rock was available on a public
website and was hyped by uninformed web users before the fresh
observations removed the risk.

Since the 1997 XF11 situation, researchers have argued, sometimes
vehemently, over how to better manage their data and make more
informative public announcements.

The Sentry system

The new Sentry system, developed over the past two years, is partly a
response to this perceived need. It is operated out of NASA's Jet
Propulsion Laboratory. The system's online "Risks Page" included 37
asteroids as of Thursday morning.

"Objects normally appear on the Risks Page because their orbits can
bring them close to the Earth's orbit and the limited number of
available observations do not yet allow their trajectories to be
well-enough defined," said JPL's Donald Yeomans, manager of NASA's
Near-Earth Object Program Office, which oversees Sentry.

"By far the most likely outcome is that the object will eventually be
removed as new observations become available, the object's orbit is
improved, and its future motion is more tightly constrained," Yeomans
said in a statement.

He added that several asteroids will be added to the list each month,
only to be removed to another "no-risk" page soon afterward.

Sentry follows other attempts to deal with the publication of asteroid
risk data. A color-coded disaster yardstick called the Torino Scale,
developed in 1999 and designed in part to inform the media and the
public, has gone largely unused. On the Torino Scale, a zero or one
represent remote risk, and a 10 means it's time to sell the farm.

All but one of the asteroids currently on the Sentry list are zeros on
the Torino Scale. Topping the list, though, is a space rock named 2002
CU11, discovered Feb. 7. It presently has a 1-in-100,000 chance of
hitting Earth on Aug. 31, 2049. But as its orbit is refined, it is
quite possible that this asteroid, like many before it, will be
categorized harmless.

Big improvement

The Sentry system is similar to another online database, called NEODys,
developed in recent years by asteroid experts in Italy. Researchers
from the two systems are cooperating to cross check results in an
effort to make both systems more effective, Yeomans said.

Sentry is "another big improvement" in the routine monitoring of
asteroids, said Benny Peiser, who runs CCNet, a scholarly electronic
newsletter that covers the threat of rocks from space.

Asteroid detections have rapidly increased in recent months, in part
because NASA has a congressionally mandated goal to find 90 percent of
all Near Earth Objects larger than 1 kilometer (0.6 miles) by 2008.
About 500 of the these asteroids have been found, and an estimated 500
or so remain undiscovered.

Sentry draws data each day from the Minor Planet Center in Cambridge,
Massachusetts, where most data about asteroids is processed. Sentry was
developed largely by Steve Chesley and Alan Chamberlin, with technical
help from Paul Chodas.
Received on Thu 14 Mar 2002 12:23:44 PM PST