[meteorite-list] Killer Space Rocks

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu, 16 Aug 2007 15:25:37 -0700 (PDT)
Message-ID: <200708162225.PAA03523_at_zagami.jpl.nasa.gov>

http://www.popsci.com/popsci/aviationspace/b9212179d0074110vgnvcm1000004eecbccdrcrd.html

Killer Space Rocks
By Kevin Krajick
Popular Science
August 2007

A recent study showed that the U.S. and China are the nations most
vulnerable to a devastating meteorite strike. With funding uncertain,
astronomers are struggling to contain the threat of a
civilization-ending galactic visitor.

What's Out There

There are between one and two million near-Earth objects (NEOs) - chunks
of space rock whose orbits may pass within 30 million miles of
Earth - that pose a significant impact threat to the planet. Of the 4,535
NEOs detected and tracked (704 of which are real whoppers), none are on
a definite collision course, but there could be millions more, many of
them potentially lethal, lurking in the cosmos.

Detection

Who's Watching? Most spotting is done by half a dozen optical telescopes
in the U.S., Italy, Japan and Australia, coordinated by such programs as
the Lincoln Near-Earth Asteroid Research (LINEAR) project, a NASA-funded
collaboration between MIT's Lincoln Laboratory and the U.S. Air Force
tasked solely with the detection and cataloging of potential NEOs.
Amateur astronomers worldwide also aid the effort. Collectively, the
programs discover a new NEO every few days.

What's the Plan?

Since 1998, NASA has funded Spaceguard, a consortium of
observatories working to find 90 percent of the half-mile-plus NEOs by
2008; the group has found three quarters of the predicted 1,100 NEOs in
this size class. Spaceguard's next step is to find 90 percent of NEOs
measuring 460 feet or larger - potentially up to 12,000 objects - by 2020,
but funding has not been secured. Larger wide-field scopes should come
online in Hawaii, Arizona and Chile in the next decade, greatly speeding
detection.

The Hot List

NASA's NEO office maintains a watch list of about 140
especially high-risk asteroids. The baddest asteroid so far is
820-foot-wide 99942 Apophis. Discovered in 2004, it briefly presented a
1-in-38 chance of collision on April 13, 2029. As more data helped
scientists to pinpoint its orbit, Apophis has since been downgraded to 1
in 45,000 in 2036 - still the biggest collision threat in the known universe.

Deflection

A handful of scientists, both at NASA and the privately funded B612
Foundation, have proposed various protocols for diverting or destroying
a collision-course NEO. None currently have funding, although the
asteroid fly-by mission Dawn will launch this month. And NASA has looked
into using existing rocket and spacecraft technology to land an
astronaut on an asteroid, a move that, if successful, could help hone
future deflection strategies. Here, a few plans on how to save the planet.

Nuke It
We already have the bombs, but the risk is that an explosion
could turn one killer asteroid into many smaller killer asteroids,
thrown into unpredictable trajectories- and radioactive.

Smack It
A spacecraft would ram the object, altering its orbit or
shattering it. Elegant, but could multiply the threats as with the bomb
scenario above.

Lean On It
A craft would push or pull the object. Not sideways - too
energy-intensive - but backward or forward to slow it down or speed it up.
A few pounds of force applied over several months would alter a
medium-size body's rate of travel such that it would miss hitting Earth
by four or five minutes and thousands of miles. An asteroid tugboat
would attach to a NEO and deliver a speed-altering nudge. A gravity
tractor would hover close to a NEO and use mutual gravitational
attraction to divert it ever so slightly. A solar sail would move a NEO
with the subtle pressure of light from the sun.
Received on Thu 16 Aug 2007 06:25:37 PM PDT