High organic content from Comet 9P/Tempel 1
Deep Impact collision ejected the stuff of life
a.. 13:10 07 September 2005
b.. NewScientist.com news service
c.. Maggie McKee
<images removed but available at the link above>
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.
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
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
"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
Journal reference: Science (DOI: 10.1126/science.1118923)