California: As scientists explore the potential for life on Mars, some of the most promising clues may come from Earth’s own deepest, oldest organisms. New findings suggest that if life exists on Mars, it could be found deep beneath its surface, where conditions may mirror those of Earth’s most extreme environments.
Mars - A Water-Rich Planet?
Recent research has unveiled significant evidence of a vast reservoir of liquid water beneath Mars' rocky crust. Data from NASA’s Mars InSight Lander, which recorded over 1,300 Marsquakes over four years, revealed that seismic waves passed through layers of wet rock, indicating considerable volumes of water locked in rocks at depths between 11.5 and 20 kilometers (7.1-12.4 miles) below the surface.
According to Vashan Wright, a geophysicist at the Scripps Institution of Oceanography, this discovery opens up the possibility that Martian life, if it exists, could thrive underground. "If they are correct, this is a game-changer," says Karen Lloyd, a subsurface microbiologist at the University of Southern California.
Earth’s deep biosphere, home to a remarkable variety of life forms, provides a potential model for understanding Martian life. For over 30 years, scientists have uncovered evidence of life existing deep underground in both oceanic and continental environments. This life primarily consists of single-celled microorganisms, such as bacteria and archaea, which have been thriving for over three billion years.
Research has shown that these microorganisms survive by harnessing chemical reactions rather than sunlight. Chemosynthesis allows them to extract energy from substances like methane and hydrogen sulfide found in rocks and water. "The subsurface has many different chemical reactions that support life," says Lloyd.
Some of these underground microbes live in environments where nutrients are scarce and temperatures are extreme. A 2018 study estimated that between 2 to 6 x 10^29 cells exist beneath Earth’s continents, highlighting the vast scale of subterranean life. This life, often in a state of slow metabolic activity due to limited food sources, might be similar to what could exist on Mars.
While no direct evidence of life has been found on Mars, features like ancient canyons suggest that the planet once had liquid water. The possibility of subterranean life on Mars is bolstered by the presence of water beneath its surface. If Mars once had a habitable environment, life may have developed deep underground and could still be surviving there.
One intriguing aspect is the presence of methane plumes in the Martian atmosphere, which could be a byproduct of microbial activity. However, Lloyd cautions that there are many potential non-biological sources for methane.
The challenge of exploring Mars’s deep subsurface is immense. Drilling through 10 kilometers (6.2 miles) of Martian crust is a formidable task, especially in a planet without breathable air or liquid water. However, upcoming missions, like NASA's Mars Sample Return mission, could help by bringing Martian rock samples back to Earth for analysis. These samples might contain traces of life.
In addition, features on Mars such as mud volcanoes may provide access to deep subsurface materials that have been exposed at the surface. Exploring these features could offer more insights into the planet's potential for life.