[meteorite-list] Sentry From Outer Space

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 10:02:32 2004
Message-ID: <200203251710.JAA27623_at_zagami.jpl.nasa.gov>

http://www.nationalpost.com/home/story.html?f=/stories/20020325/441062.html

Sentry of outer space

A NASA Web site keeps track of asteroids that could cross Earth's path

Chris Knight
National Post (Canada)
March 25, 2002

There's good news for anyone trying to calculate the end of the world.
Earlier this month, NASA launched a Web site dedicated to reporting how many
asteroids are in our planetary neighbourhood, how big they are, and how
likely it is that one will crash into Earth.

The site, called Sentry, is operated by NASA's Near Earth Object office.

Sentry offers a mixture of technical data for scientists, and general
information for people who like to gamble on when the world will come to an
end. Donald Yeomans, who manages the office in Pasadena, Calif., calls the
new site, at http://neo.jpl.nasa.gov, a "one-stop shopping place for
information on Near Earth Objects," or NEOs.

A chart on the site shows the size, speed and position of nearby asteroids,
and is updated as new ones are discovered almost daily. Thanks to a
Congressional mandate to find 90% of all very large NEOs by the end of the
decade, NASA, which knew about just 169 NEOs in 1990, has now logged more
than 1,800.

And like the info-graphics on the Weather Channel, the site also provides
animations of NEOs in orbit: Pick an object, then sit back like the occupant
of a time machine and watch the Earth swing around the Sun as the years
click by on a counter and the asteroid follows its own orbital path,
occasionally making a heart-stopping swoosh past Earth.

The asteroid 2002 DO3 is going past us right now. As you read this, it is
sailing past the Earth at 10 kilometres a second. It is about 200 metres in
diameter, big enough to carve a two-kilometre-wide crater if it hit, which
it won't -- this time. Call up its orbit on the NEO site and you can watch
it zoom harmlessly, but frighteningly close, past our planet and off into
deep space. Or look at 2002 EM7, a 60-metre-wide rock that buzzed Earth on
March 8 but was only spotted after it passed by.

Yeomans says the site, which gets thousands of visits a day, is educational
for the public: "They enjoy it and it gives them in a few seconds a view of
what the object looks like.

"And it drives home how it gets close to Earth."

NASA hopes to locate 90% of the estimated 1,000 kilometre-wide-or-larger
NEOs by the end of the decade. As of last Wednesday, the space agency was
tracking 575 kilometre-wide-or-larger NEOs. If one of these were to hit
Earth, the results would be catastrophic -- millions would be killed by an
impact near a populated area, and even an ocean strike would release enough
energy to change the climate for decades. A similar catastrophe is believed
to have wiped out most of the life on Earth 65 million years ago, killing
off the big dinosaurs and setting the stage for our own evolution.

By tracking asteroids, NASA hopes to have enough advance warning, should a
big one be heading toward Earth, to send up a spacecraft to nudge it out of
the way.

While finding NEOs is simply a matter of telescope time and patience,
tracking them is still an inexact science. Once they are discovered (by
taking consecutive pictures of a tiny part of the sky and seeing if anything
moves from one picture to the next), asteroids need to be observed over
several days to get even a rough idea of what their orbits are. Computers
can then predict their movements into the future, but the uncertainty grows
over time -- and every time an asteroid wanders past Earth or another
planet, its velocity changes.

"When you have a close approach, the uncertainties in the object's position
are magnified," says Yeomans. "We have not a clue where the object will be
several decades from now, because it could be anywhere."

He likens asteroids' orbits to railway tracks. "We know where the track is,
we know that it can intersect the Earth's path, but we don't know where it
is on the path. All you can do is come up with a best estimate of where it
will be in the future."

Yeomans says the public is becoming better educated about the risks posed by
asteroids. Nature helped in 1994, when comet Shoemaker-Levy 9 smacked into
Jupiter and space probes delivered pictures of the event. Yeomans also
credits the twin asteroid disaster movies of 1998, Deep Impact and
Armageddon, "both of which were not particularly good, but they did
sensitize the public."

Just outside modern memory, and too remote to have the impact of a Hollywood
film, was the 1908 Tunguska Event, in which an asteroid estimated at 60
metres in diameter crashed in Siberia, destroying 2,200 square kilometres of
forest with the force of a hydrogen bomb.

"You would expect something like that every 200 years or so," says Yeomans.

The NEO Web site is careful not to stir panic. The most dangerous object on
its list is asteroid 2002 CU11, highlighted in soothing green, with the
information that it has about a one-in-100,000 chance of hitting Earth -- in
2049. Even that slight risk is likely to be downgraded as the object's orbit
is more closely calculated. Still, Yeomans' office walks a fine line between
fear and education.

"We welcome a little media attention from time to time," he says. "We don't
want too much attention, though, because then our colleagues say we're nuts,
trying to increase our funding by scaring the hell out of people."
Received on Mon 25 Mar 2002 12:10:13 PM PST