[meteorite-list] NASA To Hunt Smaller Earth-Threatening Asteroids

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sat Dec 24 19:38:16 2005
Message-ID: <200512242333.jBONXLN22543_at_zagami.jpl.nasa.gov>

http://www.newscientist.com/article.ns?id=dn8510

NASA to hunt smaller Earth-threatening asteroids
Jeff Hecht
New Scientist
23 December 2005

A NASA-led search for Earth-threatening asteroids as small as 140 metres
has been approved by the US Congress and is awaiting President George W
Bush's signature. The bill provides no money, but survey telescopes are
already in development.

The asteroid search is part of a bill authorising NASA operations for
2007 and 2008. When signed, it will give NASA a year to devise a plan to
catalogue 90% of potentially Earth-threatening asteroids within 15
years. Congressional action in 1998 pushed NASA to begin its current
hunt for dangerous asteroids above 1 kilometre in size.

The new Congressional plan, pushed by California Republican Dana
Rohrabacher, echoes recommendations made in 2003 by asteroid experts.
Asteroid hunters set the original 1-kilometre target in the early 1990s
because they thought they could spot most of them.

However, at present discovery rates, NASA will not meet this target. As
of Wednesday, astronomers had catalogued 818 kilometre-class asteroids
which pose a threat to the Earth, says Don Yeomans of the Jet Propulsion
Laboratory in Pasadena, California, US. The goal is to spot 90% of all
such objects - thought to total about 1100 - by 2008, meaning there are
another 172 to go.

Balancing risk

But the 2003 asteroid panel concluded that globally devastating impacts
from large asteroids are so rare that they pose only 30% of the total
asteroid risk to humanity over long periods. Smaller impacts carry much
more risk because they are much more common.

The biggest risk, at 53%, comes from tsunami-triggering ocean impacts of
sub-kilometre objects. The remaining 17% of risk comes from
sub-kilometre impacts on land.

Balancing the risks against the difficulty of detecting small objects,
the panel recommended targeting objects measuring at least 140 metres
because they account for 90% of potential damage. However, that is well
above the size of the biggest object to hit the planet in recent
history, a 60-metre object that levelled thousands of kilometres of
forest when it exploded over the Tunguska area of Siberia in 1908.

Top-down pressure

Tracking smaller, fainter objects will require a new generation of
survey telescopes. The leading candidate is Pan-STARRS, an array of four
wide-angle 1.8-metre telescopes planned by the University of Hawaii and
funded by the US Pentagon.

Each will have detectors with 1.4 billion pixels, making them the
world's biggest digital cameras. The first telescope will begin testing
early in 2006.

Another instrument that will hunt asteroids and perform other sky
surveys is a wide-area 8.4-metre instrument called the Large Synoptic
Survey Telescope. The plan is for completion in 2012 at a cost of $300
million, but so far only design funds have been raised from the US
National Science Foundation.

"We needed some top-down pressure to go to some smaller objects," says
Yeoman. But he warns that the 140-metre Congressional target will be
tough to reach. Pan-STARRS was designed to spot objects as small as 300
metres, roughly four times brighter.

Brian Marsden, head of the Minor Planet Center at the
Harvard-Smithsonian Center for Astrophysics, adds that Pan-STARRS will
survey each part of the sky only once every four days, meaning it could
easily miss objects moving quickly across the sky when they are closest
to the Earth. Furthermore, smaller objects will be too faint to be
tracked by amateur astronomers, who now provide the follow-up
observations vital for calculating asteroid orbits.
 
Received on Sat 24 Dec 2005 06:33:21 PM PST