Express to Mars

4. THE EMISSIONS MISSION


Among the best places to look for life on Mars: anywhere there's volcanic activity. Mars has many volcanoes, including Apollinaris Patera (inset). Marvel (Mars Volcanic Emission and Life) will search for an active one that might heat an underground hydrothermal system—a warm water environment that could harbor life. The craft's two spectrometers would be so sensitive, says principal investigator Mark Allen, that "if you had just three cows anywhere on Mars, we would be able to detect the amount of methane they added to the atmosphere."