The most publicized capability of the Mars Express MARSIS (Subsurface Sounding Radar/Altimeter) is its ability to penetrate down several kilometers to detect the interface of pockets of putative liquid H2O, which has very distinct electrical properties. However, the instrument can detect many different types of interfaces, so a wide range of compositional data is possible. The only drawback, though, is that Mars Express, due to its baseline mapping orbit parameters, will not give global coverage (i.e., the highly elliptical, inclined orbit will only allow coverage of a certain latitude band).

One will also note that NASA's 2005 Mars Reconnaissance Orbiter (MRO) is slated to carry a subsurface sounding radar (SHARAD), which is to be supplied by the Italian space agency ASI, that will be used to search for water at shallower depths and different resolutions. MRO will also have the advantage, due to its planned polar orbit, of giving global coverage.

Finally, CNES's 2007 Mars PREMIER/NetLander mission will deploy a package of up to four landers on the Martian surface. The NetLanders will carry geophysical packages allowing them to characterize the local subsurface areas.

Alex R. Blackwell
University of Hawaii