Mars Express discovers new layer in Martian ionosphere (Forwarded)

ESA News
http://www.esa.int

30 November 2005

Mars Express discovers new layer in Martian ionosphere

During radio observations of the atmosphere of Mars, the MaRS
radio-science experiment on board ESA's Mars Express discovered the
presence of a previously unseen third layer in the ionosphere -- the
upper part of the Martian atmosphere.

This layer, whose existence was predicted but not detected before, is
non-continuous. Scientists believe its origin may be due to the
interaction of the ionosphere with incoming meteorites.

The MaRS experiment consists of using the radio signals that the
spacecraft uses to communicate with Earth to probe the atmosphere and
the ionosphere of Mars.

The technique, called radio-occultation, can be used when the spacecraft
'disappears' behind the planet's disk as seen from Earth: the radio
signals cross the Martian ionosphere between the spacecraft and Earth
and reveal information about the density of charged particles that
compose it.

During two Mars Express occultation seasons -- from April to August 2004
and from December 2004 to January 2005 -- MaRS detected the presence of
regions in the atmosphere where the density of charged particles
(electrons) was about one tenth of the density of the main ionospheric
layer.

These regions, localised between 65 and 110 km altitude, unambiguously
characterise a third distinct ionospheric layer below the first two,
respectively situated at 135 km and 110 km altitude.

These higher density regions were observed in a few ionospheric areas
only. Having confirmed this through several observations, scientists
concluded that this third layer is sporadic and geographically localised.

At the same time, the presence of the layer was observed at different
times of the day and latitudes -- early morning and afternoon in the
northern hemisphere of the planet, in the equatorial region and at
mid-southern latitudes.

"In any case, we do not exclude the existence of the third layer also in
the night-time portion of the ionosphere, even if we believe such
occurrence may be rare," says Martin Pätzold, MaRS Principal Investigator.

As far as the origin of this layer is concerned, Pätzold and colleagues
imagine that a mechanism similar to that occurring in Earth's ionosphere
may be in place at Mars.

On Earth, a low ionospheric layer also exists. Unlike the Red Planet, it
is non-sporadic and created by electrical charge exchange between the
atmosphere and the magnesium and iron atoms present in meteors. In fact,
it is called the 'meteoritic layer'.

"We favour the idea that the third layer is created by the influx of
meteors, like on Earth," says Pätzold. "On Mars, the atmosphere is
thinner and less dense than on Earth. Meteors then require larger
kinetic energy than on Earth to exchange charged particles above 75 km
altitude, where the Martian atmosphere becomes really thin. The
population of meteors with this energy is more limited: this could
explain the sporadic occurrence of the third ionopsheric layer on Mars,"
he concludes.

Note to editors

These scientific results appeared in the 4 November issue of the journal
Science, in an article entitled: 'A sporadic third layer in the
ionosphere of Mars'.

The authors a M. Pätzold, S. Tellmann and R. Schaa (Univ. of Koln,
Germany); B. Häusler (Univ. der Bundeswehr Munchen, Neubiberg, Germany);
D. Hinson (Stanford Univ., USA).

Mars Express was launched on 2 June 2003 and has been orbiting Mars
since December 2003. On 19 September ESA took the decision to extend the
mission by one additional Martian year (23 months), as of December 2005.

For more information

Martin Pätzold, MaRS Principal Investigator
Univ. of Koln, Germany
E-mail: paetzold.martin @ web.de

Agustin Chicarro, ESA Mars Express Project Scientist
E-mail: agustin.chicarro @ esa.int

Fred Jansen, ESA Mars Express Mission Manager
E-mail: fjansen @ rssd.esa.int

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Related links

* Mars Express instruments
http://www.esa.int/SPECIALS/Mars_Exp...C75V9ED_0.html
* Huygens instruments
http://www.esa.int/SPECIALS/Cassini-...W82VQUD_0.html
* Cassini instruments
http://www.esa.int/SPECIALS/Cassini-...182VQUD_0.html

[NOTE: An image supporting this release is available at
http://www.esa.int/SPECIALS/Results_...AUULWFE_1.html
]