There might not be much of a case for things crawling on Mars, but there might have been microbial creatures deep beneath the Red Planet’s surface before humans ever existed.
Now a team of scientists has been able to determine that it is highly possible for alien microbes to have existed several miles beneath the crust because of subsurface hydrogen that go back to billions of years ago and kept them alive for hundreds of millions of years.
"We showed, based on basic physics and chemistry calculations, that the ancient Martian subsurface likely had enough dissolved hydrogen to power a global subsurface biosphere," Brown University grad student Jesse Tarnas, who led a study recently published in Earth and Planetary Science Letters, told Phys.org. "Conditions in this habitable zone would have been similar to places on Earth where underground life exists.”
What this means is that the Martian underground could have been teeming with colonies of microbes feeding off electrons from an influx of hydrogen molecules. Something ancient Mars has in common with Earth is SliMEs. Not slime as in extraterrestrial sludge, but SliMEs as in subsurface lithotropic microbial ecosystems (lithotropes are organisms that survive off inorganic substances).
Molecular hydrogen that has been dissolved is the energy source for SliMes on our planet. The hydrogen would have reached these hypothetical microbes through radiolysis—the process by which radiation breaks down water molecules into hydrogen and oxygen. Lithotropes would have devoured electrons from those H2 molecules. Tarnas’ team suggests that around 4 billion years ago, subterranean hydrogen concentrations would have been high enough to keep swarms of microbes alive.
"The question then becomes: What was the nature of that subsurface life, if it existed, and where did it get its energy?" said Brown Department of Earth, Environmental and Planetary Sciences professor and study coauthor Jack Mustard. "We know that radiolysis helps to provide energy for underground microbes on Earth, so what Jesse did here was to pursue the radiolysis story on Mars."
Data from the gamma ray spectrometer that rides the Odyssey spacecraft around Mars was crucial for the research team, who figured out the surface concentrations of radioactive elements thorium and potassium, which also told them how much uranium was also in the soil. Radioactive decay is what makes the radiolysis that supposedly fed ancient microbes, if they existed, possible.
The team also needed to take climate into account. They concluded that there must have been a zone beneath the surface that remained habitable for eons. Surprisingly, colder temperatures would have been more effective at fueling (again, hypothetical) Martian life.
While we can’t yet prove that there really were micro-Martians thriving deep in that red soil, this research is a launching point for future spacecraft that will bring samples back to Earth.