[meteorite-list] Stardust Part II: Deep Impact Comet Revisited?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue Mar 21 22:16:12 2006
Message-ID: <200603211652.k2LGqap03972_at_zagami.jpl.nasa.gov>

http://www.newscientistspace.com/article/dn8874-stardust-part-ii-deep-impact-comet-revisited.html

Stardust Part II: Deep Impact comet revisited?
Maggie McKee
New Scientist
21 March 2006

NASA's Stardust spacecraft, which recently returned samples from Comet
Wild 2, could be called back into action to study the comet hit hard by
the Deep Impact mission in July 2005. Stardust could pick up where the
other craft left off - by imaging the crater produced by Deep Impact,
revealing the comet's interior structure.

One of Deep Impact's main goals was to study the crater gouged out by
its 370-kilogram projectile, which slammed into Comet Tempel 1 on 4 July
2005. But the impact generated more dust than expected, and that - along
with an out-of-focus camera - prevented the mother ship from imaging the
newly formed crater.

"The reason for doing the Deep Impact experiment was to find out how
comets are put together on the inside," says Deep Impact team member Joe
Veverka of Cornell University in Ithaca, New York, US.

In addition to revealing the comet's interior composition, studies of
the crater should shed light on the comet's structure and density. "If
the impactor hit something that was very hard, it would produce a
smaller crater than if it hit something very soft," Veverka told New
Scientist.

Observations of how long particles ejected by the Deep Impact collision
remained near the comet suggest Tempel 1 is actually quite soft and
spongy. "But it would be nice to verify that by looking at the crater
directly," Veverka says, adding that such information could help
scientists plan how to deflect any comets that might be discovered on a
collision course with Earth.

Valentine's Day rendezvous

Now, Veverka and colleagues are proposing that NASA image the crater
with the Stardust spacecraft in a project called ScarQuest. Stardust
captured dust from the wake of Comet Wild 2 in 2004 and dropped a
capsule full of the prized particles to Earth in January 2006.

The main spacecraft is still orbiting the Sun, moving away from the
Earth. But it has enough fuel to fire its thrusters in September 2007 to
return back towards Earth in January 2009.

That Earth flyby will put it on course to reach Tempel 1 on 14 February
2011, when the crater produced by Deep Impact will be oriented towards
the spacecraft. "Things will have settled down and cleared up, so now if
we come back, it'll be easy to see the surface," says Veverka.
          
"Mission of opportunity"

By the time it reaches Tempel 1, the comet will have orbited the Sun
once since the Deep Impact encounter. The comet is thought to lose about
a million tonnes of water vapour through evaporation on each orbit. So
scientists can compare images of its surface taken by Deep Impact as it
neared the comet during one orbit with those from Stardust during the next.

"So for the first time, we can see how much of the surface changes as
material evaporates," says Veverka. "The question is: is material
removed uniformly from everywhere? Or does it come from specific areas -
and if so, what is unusual about those areas?"

Veverka estimates that ScarQuest will cost between $20 million and $30
million. The proposal will be submitted by 5 April as a low-cost
"mission of opportunity" in NASA's Discovery programme. These are
designed to use existing spacecraft - or spacecraft parts - for new
missions. "What's neat about them is you can do them for a fraction of
the cost - 10% or less - of a new mission," Veverka says.
Received on Tue 21 Mar 2006 11:52:36 AM PST