A NASA-led research team suggests Mars' subsurface may support a microbial ecosystem powered by radioactivity-driven chemical reactions. The key requirement: the presence of liquid water, which remains unconfirmed.
Scientists searching for signs of ancient life on Mars have focused on water-deposited sediments, which on Earth preserve rich fossils. Mars, once resembling Earth, has become a cold, arid world without a magnetic field or substantial atmosphere.
For billions of years, dust storms, solar winds, and cosmic rays have battered the surface, erasing potential traces of surface life. However, Jesse Tarnas, a planetary scientist at NASA's Jet Propulsion Laboratory, proposes that some life could have retreated underground. There, radioactive elements break down water molecules through radiolysis, generating chemicals that sustain microbial communities—much like bacteria in Earth's subsurface rock pores and fissures for millions of years.
Probing Mars' subsurface could reveal if life endured. In a new study, Tarnas and colleagues analyzed Martian meteorites that fell to Earth after being ejected from the planet.
They evaluated grain size, mineral composition, and radioactive element concentrations to model crustal porosity at ejection. Computer simulations then assessed if radiolysis could produce hydrogen and sulfates—key fuels for subsurface microbes.
Published in Astrobiology, the findings indicate that with water present, radiolysis could have powered microbial communities for billions of years—and potentially still does today. Models suggest up to one million microbes per kilogram of rock. The most habitable samples originated from Mars' ancient southern highlands.
While Martian radiolysis was previously explored theoretically, this marks the first quantification using actual Martian rocks.
Such subsurface life hinges on water. Current evidence for Martian groundwater is inconclusive: recent suggestions of liquid pockets were likely clay layers. Yet hope persists.
Mars once held vast surface water, much lost to space after magnetic field collapse. A recent study estimates at least 30% of that original water remains bound in crustal minerals.
