Buried craters and underground ice -- Mars Express uncovers depthsof Mars (Forwarded)

ESA News
http://www.esa.int

30 November 2005

Buried craters and underground ice -- Mars Express uncovers depths of Mars

For the first time in the history of planetary exploration, the MARSIS
radar on board ESA's Mars Express has provided direct information about
the deep subsurface of Mars.

First data include buried impact craters, probing of layered deposits at
the north pole and hints of the presence of deep underground water-ice.

The subsurface of Mars has been so far unexplored territory. Only
glimpses of the Martian depths could be deduced through analysis of
impact crater and valley walls, and by drawing cross-sections of the
crust deduced from geological mapping of the surface.

With measurements taken only for a few weeks during night-time
observations last summer, MARSIS -- the Mars Advanced Radar for
Subsurface and Ionospheric Sounding -- is already changing our
perception of the Red Planet, adding to our knowledge the missing
'third' dimension: the Martian interior.

First results reveal an almost circular structure, about 250 km in
diameter, shallowly buried under the surface of the northern lowlands of
the Chryse Planitia region in the mid-latitudes on Mars. The scientists
have interpreted it as a buried basin of impact origin, possibly
containing a thick layer of water-ice-rich material.

To draw this first exciting picture of the subsurface, the MARSIS team
studied the echoes of the radio waves emitted by the radar, which passed
through the surface and then bounced back in the distinctive way that
told the 'story' about the layers penetrated.

These echo structures form a distinctive collection that include
parabolic arcs and an additional planar reflecting feature parallel to
the ground, 160 km long. The parabolic arcs correspond to ring
structures that could be interpreted as the rims of one or more buried
impact basins. Other echoes show what may be rim-wall 'slump blocks' or
'peak-ring' features.

The planar reflection is consistent with a flat interface that separates
the floor of the basin, situated at a depth of about 1.5 to 2.5 km, from
a layer of overlying different material. In their analysis of this
reflection, scientists do not exclude the intriguing possibility of a
low-density, water-ice-rich material at least partially filling the basin.

"The detection of a large buried impact basin suggests that MARSIS data
can be used to unveil a population of hidden impact craters in the
northern lowlands and elsewhere on the planet," says Jeffrey Plaut,
Co-Principal Investigator on MARSIS. "This may force us to reconsider
our chronology of the formation and evolution of the surface."

MARSIS also probed the layered deposits that surround the north pole of
Mars, in an area between 10 deg and 40 deg East longitude. The interior
layers and the base of these deposits are poorly exposed. Prior
interpretations could only be based on imaging, topographic measurements
and other surface techniques.

Two strong and distinct echoes coming from the area correspond to a
surface reflection and subsurface interface between two different
materials. By analysis of the two echoes, the scientists were able to
draw the likely scenario of a nearly pure, cold water-ice layer thicker
than 1 km, overlying a deeper layer of basaltic regolith. This
conclusion appears to rule out the hypothesis of a melt zone at the base
of the northern layered deposits.

To date, the MARSIS team has not observed any convincing evidence for
liquid water in the subsurface, but the search has only just begun.
"MARSIS is already demonstrating the capability to detect structures and
layers in the subsurface of Mars which are not detectable by other
sensors, past or present," says Giovanni Picardi, MARSIS Principal
Investigator.

"MARSIS holds exciting promise to address, and possibly solve, a number
of open questions of major geological significance," he concluded.

Note to editors

These findings appear on line in Science, on 30 November 2005, in an
article entitled 'Radar soundings of the subsurface of Mars'.

The authors a G. Picardi, D. Biccari, M. Cartacci, A. Cicchetti and
R. Seu (Univ. of Rome, 'La Sapienza', Italy); J.J. Plaut, A.B. Ivanov,
W.T.K. Johnson, R.L. Jordan and A. Safaeinili (NASA/JPL, Pasadena, USA);
O. Bombaci, D. Calabrese and E. Zampolini (Alcatel Alenia Space, Italy);
S.M. Clifford and E. Heggy (Lunar and Planetary Institute, Houston,
USA); P. Edenhofer (Ruhr-Univ. Bochum, Germany), W.M. Farrell (NASA
GSFC, Greenbelt, USA); C. Federico and A. Frigeri (Univ. of Perugia,
Italy); D.A. Gurnett, R.L. Huff and D.L. Kirchner (Univ. of Iowa, USA);
T. Hagfors and E. Nielsen (Max Planck Institute for Solar System
Research, Lindau, Germany); A. Herique, W. Kofman (Lab. de Planetologie
de Grenoble, France); C.J. Leuschen (J. Hopkins Univ., Laurel, USA); R.
Orosei and G. Vannaroni (Istituto Nazionale di Astrofisica, Rome,
Italy); E. Pettinelli (Univ. of Rome 3, Italy); R.J. Phillips
(Washington Univ., St. Louis, USA), D. Plettemeier (Tech. Univ. Dresden,
Germany), E.R. Stofan (Proxemy Research, Laytonsville, USA); T.R.
Watters (Smithsonian Institute, Washington DC, 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:

Giovanni Picardi, MARSIS Principal Investigator
Univ. di Roma 'La Sapienza'
E-mail: picar @ infocom.uniroma1.it

Jeffrey Plaut, MARSIS Co-Principal Investigator, NASA/JPL
E-mail: plaut @ jpl.nasa.gov

Donald Gurnett, MARSIS Co-Investigator for ionosphere studies
E-mail: Donald-Gurnett @ uiowa.edu

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

Enrico Flamini, ASI Mars Express Mission Manager
E-mail: enrico.flamini @ asi.it

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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: Images supporting this release are available at
http://www.esa.int/SPECIALS/Results_...ZTULWFE_1.html
]