[meteorite-list] Rosetta's Target Comet: Lumpy, Bumpy, Fluffy And Layered

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 24 Aug 2007 16:55:29 -0700 (PDT)
Message-ID: <200708242355.QAA00811_at_zagami.jpl.nasa.gov>

http://www.sciencedaily.com/releases/2007/08/070824134155.htm

Rosetta's Target Comet: Lumpy, Bumpy, Fluffy And Layered
Source: European Planetology Network
August 24, 2007

Science Daily - Observational and
theoretical studies of Comet 67P/Churyumov-Gerasimenko, the target of
ESA's Rosetta mission, are building a detailed portrait of the comet's
nucleus as it travels around the Sun.

Observations of the comet using the 8.2 m-ESO Very Large Telescope (VLT)
show an irregularly-shaped object that is about 4.6 kilometres in
diameter with a rotational period of 12 hours 49 minutes. Ms Cecilia
Tubiana, who will be presenting results at the second European Planetary
Science Congress (EPSC) in Potsdam on Tuesday 21st August, said, "These
observations were taken when the comet was approaching the furthest
point from the Sun in its orbit. Rosetta will rendezvous with the comet
in 2014 at a distance of about 600 million kilometres from the Sun.
While a quite detailed portrait of the comet at small heliocentric
distance has been drawn, a profound description of Rosetta's target
comet at large heliocentric distance is missing."

A team of scientists, led by the Max Planck Institute for Solar System
Research, observed the comet's nucleus in June 2004, May and August 2006
and July 2007, when the comet was at least 680 million kilometres from
the Sun. Surprisingly, although the comet was not active, they found
that a faint dust trail is visible in the images of the comet, extending
more than 500 000 km along the comet's orbital path. Ms Tubiana said,
"We believe that this dust trail is composed of large grains that the
comet shed over the many times it has travelled along this path.

Later on Tuesday 21st at the EPSC, Dr J?r?mie Lasue, of the Service
d'a?ronomie in France, will present results of numerical studies that
describe how a comet's nucleus changes as it travels along its orbital
path. Dr Lasue explained, "Comets constantly evolve by ejecting material
as their distance from the Sun changes and their temperature increases
or falls. To land on a comet's nucleus, you need to have a good idea of
its structure, density and tensile strength. Comet
67P/Churyumov-Gerasimenko most probably has an irregular comet nucleus
with crater-like depressions on its surface. Our team has developed a
three-dimensional model of the internal processes in the nucleus,
allowing us to predict the thermal evolution and surface activity as the
comet moves along its orbit."

Recent mission results suggest that a comet's structure is highly
stratified. Dr Lasue said, "Stardust showed that the dust ejected from
the outer layers is composed of fluffy particles that can be relatively
large. These particles are rich in silicates and organics, which are
the building blocks of life. Our simulations, for the first time, take
into account the relationship between the impact history of the comet
and the forces holding the comet's constituents together. This
technique has enabled us to reproduce and interpret the amazing layered
structure and surface features that Deep Impact observed at comet
9P/Tempel 1. This is a new means to quantify the tensile strength of
comet nuclei, which gives us vital information in preparing for
Rosetta's rendezvous with 67P/Churyumov-Gerasimenko."

The teams of scientists from France and Italy in which Dr Lasue works,
are developing these numerical tools to support two of Rosetta's
instruments: VIRTIS, which will determine the composition of the ices in
the comet's nucleus as well as emitted gases and dust, and CONSERT,
which will investigate the deep interior of the nucleus with radio waves.

Note: This story has been adapted from a news release issued by European
Planetology Network.
Received on Fri 24 Aug 2007 07:55:29 PM PDT