Mars Express radar collects first surface data (Forwarded)

European Space Agency
Press Release No. 38-2005
Paris, France 5 August 2005

Mars Express radar collects first surface data

Marsis, the sounding radar onboard ESA's Mars Express spacecraft, is
collecting the first data about the surface and ionosphere of Mars.

This radar started its science operations on 4 July, the same day as its
first commissioning phase ended. Due to the late deployment of Marsis,
it was decided to split the commissioning, originally planned to last
four weeks, into two phases; the second will take place in December. It
has thus been possible to begin scientific observations with the
instrument earlier than initially planned, while it is still Martian
night-time. This is the best environmental condition for subsurface
sounding, as in daytime the ionosphere is more 'energised' and disturbs
the radio signals used for subsurface observations.

As from the start of commissioning, the two 20m-long antenna booms have
been sending radio signals towards the Martian surface and receiving
echoes back. "The commissioning procedure confirmed that the radar is
working very well and that it can be operated at full power without
interfering with any of the spacecraft systems," says Roberto Seu,
Instrument Manager for Marsis, of University of Rome 'La Sapienza', Italy.

Marsis is a very complex instrument, capable of operating at different
frequency bands. Lower frequencies are best suited to probing the
subsurface, the highest frequencies are used to probe shallow subsurface
depths, while all frequencies are suited to studying the surface and the
upper atmospheric layer of Mars. "During commissioning we worked to test
all transmission modes and optimise the radar's performance around
Mars," says Professor Giovanni Picardi, Principal Investigator for
Marsis, of University of Rome 'LaSapienza'. "The result is that since we
started the scientific observations in early July, we have been
receiving very clean surface echoes back, and first indications about
the ionosphere."

The Marsis radar is designed to operate around the orbit 'pericentre',
when the spacecraft is closer to the planet's surface. In each orbit,
the radar is switched on for 36 minutes around this point, spending the
middle 26 minutes on subsurface observations and the first and last five
minutes of the slot on active ionosphere sounding.

Using the lower frequencies, Marsis has been mainly investigating the
northern flat areas between the 30 deg and 70 deg latitudes, at all
longitudes. "We are very satisfied with the way the radar is performing.
In fact, the surface measurements taken so far match almost perfectly
the existing models of the Mars topography," said Prof. Picardi. Thus,
these measurements have proved to be an excellent test. The scientific
reason for concentrating on flat regions with the first data analysis is
the fact that the subsurface layers are in principle easier to identify,
though the task is still a tricky one. "As the radar appears to work so
well for the surface, we have good reason to think the radio waves are
also propagating correctly below the surface," added Prof. Picardi.

"The bulk of our work has just started, as we now have to be sure to
clearly identify and isolate the echoes coming from the subsurface. To
do this, we have to carefully screen all data and make sure that signals
which could be interpreted as coming from different underground layers
are not actually produced by surface irregularities. This will keep us
occupied for a few more weeks at least."

The first ionospheric measurements performed by Marsis have also led to
some interesting preliminary findings. The radar responds directly to
the number of charged particles composing the ionosphere (plasma). This
has at times been shown to be higher than expected."We are now analysing
the data to find out if such measurements may result from sudden
increases in solar activity, such as the one observed on 14 July, or if
we have to put forward new hypotheses. Only further analysis of the data
can tell us," said Jeffrey Plaut, co-Principal Investigator, from the
NASA Jet Propulsion Laboratory, Pasadena, USA.

Marsis will carry on sending signals that hit the surface and penetrate
the subsurface until the middle of August, when the night-time portion
of the observations will have almost ended. After that, observation
priority will be given to other Mars Express instruments that are best
suited to operating in daytime, such as the HRSC camera and Omega
mapping spectrometer. However, Marsis will continue its surface and
ionospheric investigations in daytime, with ionospheric sounding being
reserved for more than 20% of all Mars Express orbits, under all
possible Sun illumination conditions.

In December, the Mars Express orbit pericentre will enter night-time
again. By then, the pericentre will have moved closer to the south pole,
allowing Marsis to carry out optimal probing of the subsurface once
again, this time in the southern hemisphere.

Note to editors

The first commissioning phase was given over to testing the Marsis
electronics and software and the two 20m-long antennas (dipole). The
second commissioning phase, lasting about ten days, will be spent
calibrating the 7m 'monopole' antenna. This antenna is to be used in
conjunction with the Marsis dipole to correct any surface roughness
effects caused by the radio waves emitted by the dipole and reflected by
an irregular surface. The monopole will find its best use during
investigations of areas where surface roughness is greater.

The Marsis instrument was developed within the framework of a Memorandum
of Understanding between the Italian Space Agency (ASI) and NASA. It was
developed by Alenia Spazio under ASI management and the scientific
supervision of University of Rome 'La Sapienza', in partnership with the
Jet Propulsion Laboratory (JPL) and the University of Iowa. JPL provided
the antenna manufactured by Astro Aerospace. It is the first instrument
designed to actually look below the surface of Mars.

Its major goals are to characterise the subsurface layers of sediments
and possibly detect underground water or ice, conduct large-scale
altimetry mapping and provide data on the planet's ionosphere.

For subsurface probing, Marsis must operate between 300km and 800km from
the Martian surface, while for ionospheric sounding, it has already
provided satisfactory results from a distance of up to 3000km. Radar
vertical resolution is about 150m (in free space), while horizontal
resolution, in the range of a few kilometres, depends on the
spacecraft's altitude.

The joint Italian and American Marsis team is also largely involved in
the Sharad radar, a facility instrument provided by ASI for NASA's Mars
Reconnaissance Orbiter (MRO), due for launch in August. Marsis and
Sharad are two radars designed to provide complementary information
about the Martian subsurface. Marsis can penetrate to an average depth
of 5km, while Sharad will concentrate on layers closer to the surface.

For more information:

Giovanni Picardi, Marsis Principal Investigator
Infocom Dept., Universita' di Roma "La Sapienza"
picar @ infocom.uniroma1.it

Jeffrey Plaut, Marsis co-Principal Investigator
NASA/JPL
plaut @ jpl.nasa.gov

Roberto Seu, Marsis Instrument Manager and Sharad Team Leader
Infocom Dept., Universita' di Roma "La Sapienza"
roberto.seu @ uniroma1.it

Agustin Chicarro, Mars Express Project Scientist
ESA
Agustin.chicarro @ esa.int

Fred Jansen, Mars Express
ESA
fjansen @ rssd.esa.int

Enrico Flamini, Program Manager for Italian contribution to Mars Express
ASI
Enrico.Flamini @ asi.it

Further information:

ESA Media Relations Division
Tel: +33(0)1.5369.7155
Fax: +33(0)1.5369.7690

More about...

* Looking at Mars
http://www.esa.int/SPECIALS/Mars_Express/index.html
* Mars Express factsheet
http://www.esa.int/esaSC/SEM75G1A6BD_index_0.html
* Orbiter instruments
http://www.esa.int/SPECIALS/Mars_Exp...C75V9ED_0.html

Animation

* See stages of MARSIS deployment
http://www.esa.int/SPECIALS/Mars_Exp...IC2DU8E_0.html

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IMAGE CAPTION:
[http://www.esa.int/esaCP/SEMQAN808BE_index_1.html]
This is an impression of the complete deployment of the Mars Express
MARSIS experiment, showing the two 20-metre booms and the 7-metre boom
all sprung out and locked into place.

The MARSIS experiment will map the Martian sub-surface structure to a
depth of a few kilometres. The instrument's 40-metre long antenna booms
will send low frequency radio waves towards the planet, which will be
reflected from any surface they encounter.

Credits: ESA