[meteorite-list] Rosetta Takes Comet's Temperature

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 1 Aug 2014 16:13:25 -0700 (PDT)
Message-ID: <201408012313.s71NDPgT021921_at_zagami.jpl.nasa.gov>

http://sci.esa.int/rosetta/54437-rosetta-takes-comets-temperature/

Rosetta takes comet's temperature
European Space Agency
01 August 2014

ESA's Rosetta spacecraft has made its first temperature
measurements of its target comet, finding that it is too hot to be
covered in ice and must instead have a dark, dusty crust.

The observations of comet 67P/Churyumov-Gerasimenko were made by
Rosetta's visible, infrared and thermal imaging spectrometer,
VIRTIS, between 13 and 21 July, when Rosetta closed in from 14 000
km to the comet to just over 5000 km.

At these distances, the comet covered only a few pixels in the
field of view and so it was not possible to determine the
temperatures of individual features. But, using the sensor to
collect infrared light emitted by the whole comet, scientists
determined that its average surface temperature is about -70??C.

The comet was roughly 555 million kilometres from the Sun at the
time - more than three times further away than Earth, meaning that
sunlight is only about a tenth as bright.

Although -70??C may seem rather cold, importantly, it is some
20???30??C warmer than predicted for a comet at that distance covered
exclusively in ice.

"This result is very interesting, since it gives us the first
clues on the composition and physical properties of the comet's
surface," says VIRTIS principal investigator Fabrizio Capaccioni
from INAF-IAPS, Rome, Italy.

Indeed, other comets such as 1P/Halley are known to have very dark
surfaces owing to a covering of dust, and Rosetta's comet was
already known to have a low reflectance from ground-based
observations, excluding an entirely 'clean' icy surface.

The temperature measurements provide direct confirmation that much
of the surface must be dusty, because darker material heats up and
emits heat more readily than ice when it is exposed to sunlight.

"This doesn't exclude the presence of patches of relatively clean
ice, however, and very soon, VIRTIS will be able to start
generating maps showing the temperature of individual features,"
adds Dr Capaccioni.

In addition to global measurements, the sensor will study the
variation of the daily surface temperature of specific areas of
the comet, in order to understand how quickly the surface reacts
to solar illumination.

In turn, this will provide insight into the thermal conductivity,
density and porosity of the top tens of centimetres of the
surface. This information will be important in selecting a target
site for Rosetta's lander, Philae.

It will also measure the changes in temperature as the comet flies
closer to the Sun along its orbit, providing substantially more
heating of the surface.

"Combined with observations from the other 10 science experiments
on Rosetta and those on the lander, VIRTIS will provide a thorough
description of the surface physical properties and the gases in
the comet's coma, watching as conditions change on a daily basis
and as the comet loops around the Sun over the course of the next
year," says Matt Taylor, ESA's Rosetta project scientist.

"With only a few days until we arrive at just 100 km distance
from the comet, we are excited to start analysing this fascinating
little world in more and more detail."


More about Rosetta

Rosetta is an ESA mission with contributions from its member
states and NASA. Rosetta's Philae lander is provided by a
consortium led by DLR, MPS, CNES and ASI. Rosetta will be the
first mission in history to rendezvous with a comet, escort it as
it orbits the Sun, and deploy a lander.

Comets are time capsules containing primitive material left over
from the epoch when the Sun and its planets formed. By studying
the gas, dust and structure of the nucleus and organic materials
associated with the comet, via both remote and in-situ
observations, the Rosetta mission should become the key to
unlocking the history and evolution of our Solar System, as well
as answering questions regarding the origin of Earth's water and
perhaps even life.


For more information, please contact:

Markus Bauer
ESA Science and Robotic Exploration Communication Officer
Tel: +31 71 565 6799
Mob: +31 61 594 3 954
Email: markus.bauer at esa.int

Matt Taylor
ESA Rosetta project scientist
Email: matthew.taylor at esa.int

Fabrizio Capaccioni
VIRTIS principal investigator
INAF-IAPS, Rome, Italy
Email: fabrizio.capaccioni at iaps.inaf.it
Received on Fri 01 Aug 2014 07:13:25 PM PDT