Habitability of the Shallow Subsurface on Mars: Clues from the Meteorites

The properties that define habitability are commonly understood to include the following:
- Presence of water.
- Temperature range allowing some or all of the water to be liquid.
- A suitable physical volume or space permitting metabolism and growth.
- Presence of organic compounds or the building blocks to make them.
- Presence of an energy source suitable for utilization by living organisms.

Interpretations of Mars Viking, Surveyor, and Odyssey orbital images have built a strong case that Mars had surface water during its past geological history. Neutron spectrometer data from Mars Odyssey show that poleward of about 60 degrees North and 60 degrees south, significant hydrogen, likely as ice or permafrost, is present in at least the upper meter or so of the Martian regolith and crust and that similar high hydrogen areas exist, even near the equator. Here we present a summary of independent data from the Mars meteorites showing that liquid water was present for at least some of the time in the upper few meters or tens of meters as early as 3.9 billion years (Ga), and was present at intervals and at various locations throughout most of Mars history.