[meteorite-list] Asteroid's Path Could Put Earth In Its Sights (Aphophis)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Aug 30 13:04:16 2005
Message-ID: <200508301645.j7UGjTw12267_at_zagami.jpl.nasa.gov>

http://www.usatoday.com/tech/science/space/2005-08-28-asteroid-impact_x.htm

Asteroid's path could put Earth in its sights
By Dan Vergano
USA TODAY
August 29, 2005

Astronomers are debating what to do about Earth's close encounter with
an asteroid in 2029 and again in 2036 - passages that might be too close
for comfort.

Apophis, a 1,059-foot-wide asteroid, has excited astronomers since it
was spotted last year. After observing it for a while, scientists
concluded that it has only a 1-in-8,000 chance of ever smacking into
Earth. But even that slim chance has them talking and NASA pondering how
to keep track of it - just in case.

"The most likely turn of events is that it will miss us," says Steve
Chesley of NASA's Jet Propulsion Laboratory in Pasadena, Calif., which
has monitored the asteroid since December as part of its normal watch
over "near-Earth" asteroids. "We are prepared for the worst but
certainly don't want to act too hastily."

In June, former astronaut Russell Schweickart petitioned NASA chief
Michael Griffin to consider placing a transmitter on Apophis, which is
named after an ancient Egyptian god of darkness and destruction, by
2013. Chesley says NASA will respond in a few weeks.

The key question about Apophis is whether its 2029 trajectory will go
through a roughly 2,000-foot-wide region called a "keyhole," says
astronomer Clark Chapman of Southwest Research Institute in Boulder,
Colo. If it passes through that region - that one-in-8,000 chance - its
course would be deflected to make an impact with Earth in 2036 very
likely, he says.

This asteroid passes near Earth every seven or eight years, but the 2029
trajectory is expected to be its closest approach. In the petition,
Schweickart warned that waiting for better estimates of Apophis' likely
path in 2020, after another flyby of Earth, would leave little time to
deflect the asteroid away from the keyhole.

If the asteroid were to strike Earth, scientists say the impact would be
felt somewhere on a line stretching from Japan to the Caribbean. It
would create a roughly 2-mile-wide crater and possibly create a tsunami.

But Chesley says directing the asteroid away from Earth might take only
a blast the size of NASA's "Deep Impact" mission, which smacked a probe
into the comet called Tempel 1 in July. A 2029 deflection mission would
be easier because an asteroid practically saunters compared with the
speed of a comet, and this one passes within 22,600 miles of Earth's
center -"extraordinarily close for an object of this size," he says.

The asteroid should be visible, about as bright as the stars in the Big
Dipper constellation, to observers in Europe, Chapman says. Such a close
asteroid flyby comes only once every 1,500 years. "Certainly this is a
profound scientific opportunity," Chesley adds.

Astronomers already are pondering what the 2029 encounter will do to the
asteroid. The Earth's gravity will exert strong tidal forces on Apophis,
which could change the asteroid's shape if it is only a loose
agglomeration of rock. The flyby also will permanently alter the
asteroid's orbit, although how is still uncertain.

Radar observations next spring should improve estimates of the
asteroid's path and might indicate a lower impact risk.

"But there are more asteroids out there, so we should be paying
attention," Chapman says.
Received on Tue 30 Aug 2005 12:45:28 PM PDT


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