Could life on Mars be hiding deep underground?

Typically, Mars missions look for signs of life on the planet's surface at sites that show signs of ancient water (a reliable indicator of where life might have been found on Earth).

Beneath the surface of Mars is believed to be an area rich in bacteria.

But while no life has yet appeared on the surface of Mars, there may be plenty of microbes lurking underground, according to research presented recently at the annual meeting of the American Geophysical Union (AGU).

In fact, in recent decades, underground explorations on Earth have revealed what is known as the deep biosphere—an environment below Earth's surface teeming with microorganisms. And scientists suspect that a similar region may also thrive beneath the surface of Mars.

Billions of years ago, when the planets in the Solar System were “young,” the surface of Mars looked quite similar to Earth. However, everything changed when Mars was hit by strong radiation from space, making survival on the surface of the red planet extremely difficult, said researcher Michalski.

Scientists believe that life first appeared on Earth about 3.8 billion to 3.9 billion years ago. Perhaps life arose on Mars at the same time as on Earth, but adapted to life underground.

Meanwhile, the Earth's deep biosphere was first discovered only about 30 years ago, but it is an extremely important discovery because the microorganisms living in this deep biosphere account for nearly half of all life on the planet.

“We are at a point where it is really the frontier of understanding what the ‘deep biosphere’ really means on Earth and how it relates to other planets in our Solar System,” says researcher Michalski. “It is a window into our origins.”

Now, in a new perspective, scientists say the Martian subsurface is an especially promising place to start looking for extraterrestrial microbes because it is even more hospitable to microorganisms than Earth's deep biosphere.

Subsurface rocks on Mars are also more porous than on Earth — creating pockets for the exchange of nutrients and gases — and Mars' colder core provides more comfortable temperatures for microbes living in deep rocks, Michalski added.