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Planetology

Radar Probes Martian Waters

radar

© NASA/JPL/ASI/ESA/Univ. of Rome/MOLA Science Team/USGS

This map shows the thickness of the south polar layered deposits of Mars, from the thinnest areas (in purple), to the thickest (in red) The dark circle in the upper center is the area poleward of 87 degrees south latitude, where MARSIS data cannot be collected.


Recent findings proving the existence of a Martian hydrosphere have renewed the possibility that the planet might have once been able to sustain life. The Mars Advanced Radar for Subsurface and Ionospheric Sounding or MARSIS1 has revealed that the southern pole of Mars forms an ice dome that stretches across 1000 km in diameter.2 The total volume of ice spans approximately 1.6 million km3 extending from the surface downward, which would cover the planet with 11 meters of water if it were uniformly spread out. Set up in 2005 as part of the Mars Express probe project, MARSIS employs radar echo sounding technology to identify geological strata below the planet's surface, the same method used for exploring ice sheets and glaciers on Earth. The radar sends low-frequency waves that penetrate 3.7 km into the planet. The time delay between the signal and its echoes is correlated with the structure of underground deposits. MARSIS revealed that radar signals were only slightly attenuated as they travelled beneath the polar caps, suggesting that substrata at these extremities are composed of nearly pure water ice with only a small component of dust.

“In the past, we only had estimations of the amount of water present in polar regions on Mars. Today, MARSIS has given us the opportunity to yield actual measurements,” says Wlodek Kofman, from the Grenoble Planetology Laboratory.3 The radar also determined the variation in distribution and depth of the ice below the surface. It located impressively large depressions that were up to 200 km wide and 1 km deep in relation to the average level of the substrata.

Data also made it possible to draw the first set of topographic maps describing the subsurface of Mars. The Grenoble laboratory collaborated on interpreting these data. The simulator developed in Grenoble (in collaboration with JPL4) was used to separate signals coming from the surface and subsurface of the planet.

In parallel, MARSIS was used for studying other components of the planet. “Among other things, we've been able to elucidate the ionosphere with an extent of space coverage around the planet that had never yet been attained,” concludes Kofman.

 

Melisande Middleton

Notes :

1. www.marsis.com
2. Plaut et al., “Subsurface Radar Sounding of the South Polar Layered Deposits of Mars,” Science. 316: 92-5. 2007.
3. Laboratoire de Planétologie de Grenoble (CNRS / Université de Grenoble).
4. The NASA Jet Propulsion Laboratory.


Contacts :

Laboratoire de Planétologie de Grenoble.
> Wlodek Kofman,
wlodek.kofman@obs.ujf-grenoble.fr
> Jérémie Mouginot,
jeremie.mouginot@obs.ujf-grenoble.fr


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