Probe Begins Studies Of Martian Ionosphere
The European Space
Agency's Mars Express radar, or MARSIS, has been deployed on the
first phase of its operations for more than four months. The ESA
has released its status report on the orbiter.
For the operational period up to now, Mars Express has been
making its closest approaches to Mars predominantly in the daytime
portion of its orbit. The MARSIS radar’s scientists are
mainly collecting data about the highly electrically conductive
upper layers of the Martian atmosphere, or 'ionosphere,' which
appears to be maintained by sunlight.
Scientists are also continuing analysis of all data gathered
during the first night-time observations last summer, especially in
the search for and interpretation of possible signals from
subsurface layers. This includes the search for a possible
signature of underground water, in frozen or liquid state.
Different materials are characterised by their 'dielectric
constant' -- the specific way they interact with electromagnetic
radiation, such as radio waves. When a radio wave crosses the
boundary of different layers of material, an echo is generated and
carries a sort of "fingerprint" from the specific materials.
From the time delay for an echo to be received by the radar
instrument, the distance or the depth of the layers of material
producing the echo can be deduced.
While the Mars Express point closest approach is in daylight,
MARSIS is only operating at higher frequencies within its
capability because the lower-frequency radio signals get disturbed.
With these higher frequencies, MARSIS can study the ionosphere and
the surface, while some shallow subsurface sounding can still be
attempted. During night-time observations, like those performed
briefly last summer immediately after deployment, it is possible
for MARSIS to use all frequencies for scientific measurements,
including the lowest ones, suitable for penetrating under the soil
of Mars.
Tuning to different frequencies for different targets in
different conditions is not the only secret of MARSIS. The
instrument, responding to signals reflected from any direction,
requires scientists also do a huge amount of analysis work to
remove these interfering signals from the echoes.
A typical example of what they look for is 'clutter
backscattering', which are reflections apparently coming from the
subsurface, but actually produced by irregularities in the surface
terrain that delay the return of the echo. For this "cleaning"
work, the team also makes use of surface echo simulator computer
programs.
In the first months of operations, MARSIS performed its first
ionospheric sounding. The data are converted into typical plots,
called ‘ionograms’, where the altitude at which the
echo was generated, deduced by the echo time delay, is given for
each transmitted frequency. The intensity of the various echo
signals detected is indicated in different colours.
In parallel to the analysis of surface and subsurface signals,
the scientists are studying all ionograms to draw the first
conclusions on the nature and behavior of the ionosphere of Mars,
and of its interaction with the planet and the surrounding
environment.
ANN's Daily Aero-Term (11.29.25): Waypoint
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