Buried craters and underground ice -
Mars Express uncovers depths of Mars
MARSIS 'radargrams' of buried basin on Mars
30 November 2005
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. audio interview
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.
Topographic map of Chryse Planitia with location of possible buried basin
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 radargram of north polar layered deposits
MARSIS also probed the layered deposits that surround the north pole of Mars, in an area between 10º and 40º 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 are: 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
 At Saturn and Titan (http://www.esa.int/SPECIALS/Cassini-Huygens/index.html)  Looking at Mars (http://www.esa.int/SPECIALS/Mars_Express/index.html)
Related articles
 Mars Express evidence for large aquifers on early Mars (http://www.esa.int/SPECIALS/Results_from_Mars_Express_and_Huygens/SEMA1UULWFE_0.html)  Mars Express radar reveals complex structure in ionosphere of Mars (http://www.esa.int/SPECIALS/Results_from_Mars_Express_and_Huygens/SEMB4UULWFE_0.html)  Mars Express discovers new layer in Martian ionosphere (http://www.esa.int/SPECIALS/Results_from_Mars_Express_and_Huygens/SEMIAUULWFE_0.html)
Related links
 Mars Express instruments (http://www.esa.int/SPECIALS/Mars_Express/SEMUC75V9ED_0.html)  Huygens instruments (http://www.esa.int/SPECIALS/Cassini-Huygens/SEM9W82VQUD_0.html)  Cassini instruments (http://www.esa.int/SPECIALS/Cassini-Huygens/SEMY182VQUD_0.html)
Bild:Mars_Viking_11h016.png|thumb|Landegebiet um die Sonde „Viking 1“ in Chryse Planitia, Juli 1976

 Forscher der Europäischen Raumfahrtorganisation ESA entdeckten mit Hilfe der Sonde „Mars Express“ und deren Tiefenradar „Marsis“ eine bis zu 250 Kilometer große und teilweise einen Kilometer dicke, runde Struktur unterhalb der Oberfläche des Mars im Krater Chryse Planitia, die möglicherweise aus Eis besteht.

Mars Express ist seit dem 2. Juni 2003 auf Marskurs und umkreist unseren Nachbarplaneten seit zwei Jahren. Am 19. September hatte die ESA entschieden, die Marsmission um ein Marsjahr auszudehnen. Der Mars umkreist die Sonne in 23 Monaten einmal, braucht für eine Umrundung der Sonne also ungefähr zwei Erdenjahre.

Vermutungen über das Vorhandensein größerer Wasservorkommen auf dem Mars hatte es bereits seit längerem gegeben. Bisher war der Nachweis jedoch noch nicht gelungen. Das jetzt gefundene Wassereis beflügelt Theorien, wonach sich auf dem Mars möglicherweise einfache Lebensformen wie Mikroorganismen entwickelt haben könnten.

Die Entdeckung gelang mit Instrumenten, die den Marsboden bis zu einer Tiefe von einem Kilometer durchleuchteten. Die Wasservorkommen in dieser Tiefe seien ausgedehnte Eismassen, die eine Temperatur von minus 33 Grad Celsius hätten. Das Feld habe einen Durchmesser von 250 Kilometern.

Über die Entstehung der Wasserflächen wurde eine Theorie entwickelt, die einen Vulkanausbruch als Ursache der unter der Oberfläche vorhandenen Eisvorkommen postuliert. Der Planetenforscher Ralf Jaumann von der Deutschen Gesellschaft für Luft- und Raumfahrt vermutet, dass durch vulkanische Aktivität Wassereis auf der Oberfläche geschmolzen und durch Gesteinsrisse in die Tiefe gesickert sein könnte. Weitere Eisvorkommen werden am Mars-Nordpol und in Äquatornähe vermutet.

Die neuen Forschungsergebnisse wurden am 30. November 2005 in der Zeitschrift „Science“ veröffentlicht.