[meteorite-list] Deep Impact Collision Ejected the Stuff of Life

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed Sep 7 16:12:13 2005
Message-ID: <200509071946.j87JkgK14994_at_zagami.jpl.nasa.gov>

http://www.newscientistspace.com/article/dn7961-deep-impact-collision-ejected-the-stuff-of-life.html

Deep Impact collision ejected the stuff of life
Maggie McKee
New Scientist
07 September 2005

Millions of kilograms of fine dust particles and water and a
"surprisingly high" amount of organic molecules sprayed into space when
NASA crashed its Deep Impact spacecraft into Comet 9P/Tempel 1 on 4 July
2005, reveal a trio of new studies.

The observations bolster theories that comets may have seeded Earth with
the raw materials for life and suggest they may be sponge-like - rather
than hardened - at their cores.

On 4 July, about 80 telescopes on Earth and in space trained their
sights on Comet Tempel 1 when a 370-kilogram copper impactor was sent
hurtling into its path. Just after the smash, a bright vapour plume
spewed from the surface at about 5 kilometres per second, followed
quickly by a stream of particles that spread into a cone.

The cone appeared to remain attached to the comet's surface for about 22
hours before separating into a detached arc. Researchers used this
gravitational attraction to estimate the mass and density of the comet's
main body, or nucleus. They found that the 72 trillion kilogram-nucleus
was extremely porous, with as much as 80% of its volume taken up by
empty space.

"That tells me there is no solid layer all the way down to the centre,"
says Mike A'Hearn, the mission's principal investigator at the
University of Maryland in College Park, US. He says he had expected that
the ice might become denser towards the core of the nucleus, but that
instead "probably all the way in, ice is all in the form of tiny grains".
          
A touch crumbly

"It's like a sponge, with a lot of cavities," agrees Horst Uwe Keller,
an astronomer at the Max-Planck Institute for Solar System Research in
Germany. He observed the event with Europe's Rosetta spacecraft and says
the discovery confirms previous observations suggesting other comets are
also porous. "When you touch it, it just crumbles under your hands."

Observers estimate the impact released about 5 million kilograms of
water from beneath the comet's surface and between two and five times as
much dust. There was so much dust, in fact, that mission members have
not been able to see the impact crater with the high-resolution camera
on the mission's flyby spacecraft, about 500 km away.

To add to the problem, that camera was malfunctioning but now
image-processing techniques may have revealed a glimpse of the crater
and team members may release the image later on Wednesday.
          
Building blocks

The team estimates the impact blasted away a crater about 100 metres
wide and up to 30 m deep. Crucially, organic molecules were among the
material ejected. Neither the full range of molecules nor their
abundances have been determined yet, but researchers say they have found
a surprisingly high amount of methyl cyanide, a molecule seen in large
quantities in another comet.

This supports theories that comets may have brought water and the
building blocks of life to Earth, and the team hopes to eventually
"identify all the species comets brought in abundance to early Earth",
says A'Hearn.

The observations have also apparently ruled out another theory - that
impacts with other objects may be responsible for the occasional stream
of gas and dust seen coming off of comets. Although Tempel 1's surface
is pockmarked with craters ranging from 40 m to 400 m across,
astronomers watching the comet both before and after the impact noticed
that it released the streams relatively often in spurts of activity
apparently triggered by sunlight.

"I don't think the hypothesis that outbursts are caused by impacts is
really valid," says A'Hearn. "Probably comets undergo outbursts like
this very frequently and the fact that everyone was looking intensively
[at this comet] for an extended period allowed us to see phenomena that
are probably common and weren't seen before."

Journal reference: Science (DOI: 10.1126/science.1118923)
Received on Wed 07 Sep 2005 03:46:41 PM PDT