Among our solar system’s planets, Mars seems a likely spot for future human habitation. Elon Musk is developing an interplanetary vehicle that may someday transport Martian colonists. Science fiction writers often discuss it as a target for future terraforming efforts. There are even research stations here on Earth today where scientists can simulate living on Mars. Numerous books have been written about our fascination with this fourth planet from the Sun.

One aspect of the Red Planet’s allure is the prospect that it harbors life. Since the 19th century, there has been significant speculation that extraterrestrials may live there. We have by now, however, quite thoroughly explored the surface of Mars with no definitive indication of life.

The next step in testing whether Martian life exists is to explore the planet’s subsurface. We spoke with Dr. Vlada Stamenkovic of NASA’s Jet Propulsion Laboratory to learn more about the value of Martian subsurface exploration.

***

How much do we know about the interior of Mars and how do we know it?

We do not know yet much about the interior of Mars. We have data from orbiters on topography (from gravity) and on ices at the poles (from radars such as Marsis and Sharad). InSight is currently exploring on Mars the deep interior over scales of hundreds to thousands of kilometers, which will revolutionize our understanding of large-scale structures in the Martian interior (meaning the mantle and core). What I am fascinated by is whether there were or still are potential habitats for life in the Martian subsurface and whether there are resources, such as water ices, for future human explorers. Hence, the region I am keen on further exploring is the shallow crust – from meters to kilometers.

For that matter, how much do we know about the interior of our own planet?

We know much more about our own planet’s interior – on large and small scales from various techniques such as seismology, EM techniques such as TEM, radar, drilling, and many more. However, in relation to deep life – meaning life in the subsurface – we are just starting the learning process. A few shy decades ago, we wouldn’t have believed that there is microbial life at depths of a few hundred meters or multiple kilometers. Today we know that the deep biosphere might be just as rich in biomass as all life on the planet’s surface.

Why would it make sense to look for life on Mars in the subsurface?

The Martian surface is enormously hostile to life as we know it. Radiation, cold, and oxidative chemistry destroy organic matter. Furthermore, liquid water is generally not stable on the Martian surface. The subsurface on the other hand is a shielded environment, where liquid water can exist, where temperatures are warmer, and where destructive radiation is sufficiently reduced. Hence, if we are searching for life on Mars, then we need to go beneath the surficial Hades.