[meteorite-list] Mars Express - 5000 Orbits and Counting

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Fri, 30 Nov 2007 09:45:42 -0800 (PST)
Message-ID: <200711301745.JAA14111_at_zagami.jpl.nasa.gov>


Mars Express - 5000 orbits and counting
European Space Agency
23 November 2007

On 25 December 2003, Europe's first Mars orbiter arrived at the Red
Planet. Almost four years later, Mars Express continues to rewrite the
text books as its instruments send back a stream of images and other
data. Today, the spacecraft reached another milestone in its remarkable
career by completing 5000 orbits of Mars.
During its mission to investigate martian mysteries, the orbiter has
revolutionised our knowledge of Mars, probing every facet of the Red
Planet in unprecedented detail. Some of the most visually astonishing
results have been returned by the High-Resolution Stereo Camera (HRSC),
which has produced breathtaking, 3D colour images of the diverse martian
surface - with giant volcanoes to sinuous valleys and ice-modified craters.

One of the most surprising discoveries has been the youthful appearance
of the country-sized volcanoes of the Tharsis ridge, suggesting they may
have been active only a few million years ago. The images also show that
glacial landforms are widespread over much of the planet, with glacial
activity continuing in some areas until perhaps 20 000 - 30 000 years
ago. Among the peculiar landforms imaged by HRSC is what appears to be a
recently frozen body of water in Elysium, close to the equator.

While the camera has been imaging the surface in exquisite detail, other
instruments have been examining different aspects of the planet's
environment. One of the most significant results from the Visible and
Infrared Mineralogical Mapping Spectrometer OMEGA has been the discovery
of clays, hydrated minerals that formed early in the planet's history,
when liquid water was fairly abundant. However, the presence of
sulphates and iron oxides suggests that the planet subsequently became
colder and drier, with only episodic eruptions of water onto the surface.

At the poles, OMEGA has measured the surface composition and produced
unprecedented maps of water ice and carbon dioxide ice. Further insights
into the martian poles have come from the Mars Advanced Radar for
Subsurface and Ionospheric Sounding, MARSIS, which is revealing, for the
first time, the secrets of the planet's subsurface.

It has so far identified the presence of water ice deposits several
kilometres underground and revealed fine, layered material near the
poles. Similar soundings of the north polar cap have confirmed that it
is dominated by water ice, with variable amounts of dust. The larger
southern cap seems less dusty, but, with a maximum thickness of 3.7 km,
it contains enough ice to produce a global ocean 11 m deep.

The multi-frequency radar has also been probing the upper atmospheric
layer (the ionosphere) and found that the distribution of charged
particles is linked with patchy magnetic fields in the martian crust.

Although Mars' atmosphere is very thin, it plays an important role in
the planet's evolution, and new breakthroughs have been made possible by
Mars Express. The Planetary Fourier Spectrometer (PFS) has made the most
complete map to date of its chemical composition. Evidence for the
presence of methane could indicate that volcanic activity, or even
simple lifeforms may still be present today.

Meanwhile, the Ultraviolet and Infrared Atmospheric Spectrometer, SPICAM
has provided the first complete vertical profile of the atmosphere's
carbon dioxide density and temperature. It has revealed a nightglow and
aurorae at mid-latitudes, produced the first ozone map and discovered
the highest clouds ever observed on Mars.

The Energetic Atoms Analyser (ASPERA) has confirmed that the solar wind
is slowly stripping atoms from the atmosphere down to an altitude of 270
km, although the rate of loss is surprisingly slow.

The MaRS radio science experiment has studied surface roughness by
pointing the craft's high-gain antenna at the planet and recording the
echoes. It has also been used to measure small changes in the
spacecraft's orbit caused by gravity anomalies. Some of the most marked
increases in surface gravity have been found over the volcanic Tharsis
ridge, indicating a higher-than-average crustal density. Another
discovery has been the existence of an ionospheric layer created by
meteors burning up in the atmosphere.

With the mission already extended until at least 2009 and the
possibility of further extensions into the next decade, ESA is keen to
ensure that Mars Express will continue to provide the best possible
scientific return. In an effort to meet the needs of the various science
teams with instruments on Mars Express, controllers at ESA's Space
Operations Centre in Darmstadt, Germany, are currently fine-tuning the
spacecraft's orbit.

"Between 18 November and 16 December, the thrusters will be fired five
times to make minor alterations to the orbit," said Tanja Zegers, Mars
Express Science Operations Co-ordinator.

"This will ensure that HRSC and OMEGA will continue to have suitable
lighting conditions for their observations in the future, while meeting
the needs of the MARSIS scientists, who need observing time at night to
look beneath the surface. It will also enable the imaging instruments to
continue their programme of detailed observations, so that they can
eventually complete the global mapping of the planet."
For more information :
Agustin Chicarro, Mars Express Project Scientist
Email: Achicarr _at_ rssd.esa.int

Tanja Zegers, Mars Express Science Operations coordinator
E-mail: Tanja.Zegers _at_ esa.int
Received on Fri 30 Nov 2007 12:45:42 PM PST

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