[meteorite-list] Starting a shootin' war with the Martians

From: Darren Garrison <cynapse_at_meteoritecentral.com>
Date: Thu Jan 26 22:38:11 2006
Message-ID: <pl5jt1h3esk23rmsu32j03hb6qtomh38o4_at_4ax.com>

http://www.newscientistspace.com/article.ns?id=dn8637

'Wrecking ball' could break the ice on Mars
11:58 26 January 2006
NewScientist.com news service
MAggie McKee

A plan to drop a quarter-tonne copper ball through Mars's atmosphere and study
the ejecta it blasts away from the planet's surface on impact is to be proposed
to NASA.

The mission, called THOR, would test models suggesting the planet's tilt ? and
therefore its climate ? swings through extreme changes every 50,000 years.

Robotic landers and rovers have previously visited the Red Planet's equatorial
regions, and an upcoming mission called Phoenix is due to touch down near the
north pole in 2008. But no probe has visited the planet's mid-latitudes, where
gullies and glacier-like features suggest there may be large amounts of pure
water ice beneath a layer of dusty soil.

Now, researchers led by Phil Christensen at Arizona State University in Tempe,
US, are proposing a mission to search for that ice directly. The idea behind
THOR (Tracing Habitability, Organics, and Resources) is to fly an observer
spacecraft to Mars and, hours before it reaches the planet, release an
"impactor" ball. It could be up to 230 kilograms in mass and would be aimed at a
region about 40? north or south of the equator.

The impactor, likely to be a giant copper sphere, would crash to the surface at
more than 4 kilometres per second, blasting a crater about 10 metres deep.
Meanwhile, the observer spacecraft would record the event from orbit, studying
the composition of the ejected soil with spectrometers.

Pure snow
"It's neat because it's a brute force way to gain access to the subsurface of
Mars," says David Spencer, a team member at NASA's Jet Propulsion Laboratory in
Pasadena, California, US. "The impactor will be very simple and we'll get our
first look at material from that depth."

Christensen says that will provide a crucial test for models of Mars's past
climate. "The climate models predict that as the orbit of Mars evolves, the tilt
of its spin axis changes," he told New Scientist. Over a 50,000-year timescale,
the planet can tilt from 10? to 40? ? or anywhere in between, he says.

When the planet is tilted most drastically on its side, the planet's poles
receive a lot of sunshine. Any water locked in ice there is thought to vaporise
and move towards the equator, where it falls as snow. "The climate can change
dramatically and deposit as much as 10 or 20 metres of pretty much pure snow in
the mid-latitudes," Christensen says.

Reconnaissance mission
THOR, named after the hammer-wielding Norse god of thunder, would prove this
snow theory right if it measures mostly water in the plume of ejected material,
he says. But if it reveals mostly dirt, that would lead researchers back to the
drawing board, he says: "Maybe the idea of climate change, and tilt, and the
deposition of snow [is wrong], or maybe not as much ice moves around."

The mission would also be able to detect organic compounds, such as methane, in
the ejecta and the atmosphere. The compounds are intriguing because they might
signal the presence of life, but THOR would not carry the instruments to prove
it unequivocally.

"I view this as a reconnaissance mission to see if these regions are rich in
ice," says Christensen. "And if they are, to use that as a rationale to go back
to these regions with future rovers and explore them in more detail."

Christensen's team will submit a preliminary proposal for the $450 million
mission to NASA in July. If it is selected to fly, it could launch as soon as
2011.
Received on Thu 26 Jan 2006 10:44:18 PM PST