Scientists have made a discovery about Mars that could lead to uncovering alien life.

They identified an 1,800-mile-wide plain in the northern hemisphere that has the right subsurface conditions to support living organisms.

The region - called Acidalia Planitia - contains just the right levels of water, heat and energy in its soil for alien bacteria to thrive. 

The next step is to drill into the Martian surface to see if life truly has sprung there.

'[It is] a promising target area for future missions in the search for extant life in Mars' subsurface,' the researchers, led Andrea Butturini of the University of Barcelona, wrote.   

But researchers would have to dig miles below the Red Planet. This would require major crewed missions and technologies that are not likely to be achievable for years to come.

This study, however, brings scientists one step closer to finding definitive proof of live beyond Earth by zeroing-in on a location where microbial life could exist.

What's more, it lays the groundwork for future studies that could settle an 'intense debate' about the presence of methane in the Red Planet's atmosphere.

That's because the alien life forms that the researchers believe could live beneath Acidalia Planitia are methanogens, or methane-producing bacteria.

Methanogens are extremophiles - bacteria that thrive in extreme environmental conditions such as very high temperatures, ultra-salty water or even high levels of radiation. 

On Earth, methanogens typically dwell in swamps and marshes but can also be found in the guts of cows, termites and other herbivores, as well as in dead and decaying organic matter. 

These microorganisms are anaerobic, which means they do not need oxygen to survive. They can also survive without organic nutrients or sunlight. 

In 2028, the European Space Agency (ESA) plans to launch their Rosalind Franklin rover, previously known as the ExoMars rover. 

This will include a drill that can dig roughly seven feet into the Martian surface.

But that's not nearly deep enough to access the potentially habitable depth Butturini and his colleagues identified.

The Martian surface is inhospitable due to extremely cold temperatures and low pressure that not even extremophiles could survive.

But below the surface, the radioactive decay of elements such as thorium - a radioactive metal - produces heat and chemical energy. What's more, water left behind from ancient oceans is buried within the Red Planet.

These conditions could provide the ingredients for bacterial life - but likely up to five miles below. 

Butturini, a biogeochemist the University of Barcelona, and his colleagues used data from Mars orbiters to locate regions where abundant thorium could provide life-sustaining energy.

They then matched this data with the distribution of subsurface ice previously mapped by missions such as the Chinese Zhurong rover.

This analysis revealed that the 'most robust target area is the southern Acidalia Planitia at mid latitude,' located near a region of clay and carbonate deposits with signs of groundwater activity.

At this underground location, temperatures are higher than they are on the surface, averaging between 32 to 50°F. 

That means liquid water could be mixed into the Martian soil. And where there is liquid water, bacterial life can grow. 

The findings are currently available on the pre-print server arXiv, which means the study has yet to be reviewed by other scientists. 

But the research is already gaining attention from the scientific community, as it provides a specific location on which to focus the search for extraterrestrial life.

'The subsurface of the southern of Acidalia Planitia is a putative target region for hosting cold-adapted Methanosarcinaceae-like and/or Methanomicrobiaceae-like methanogens,' the study reads.

'In this region, the radiogenic heat-producing elements are at the highest abundance and subsurface water is likely.'

If the researchers' theory eventually proves correct, it would not only lead to the groundbreaking discovery of alien life on Mars, but it would also provide indirect evidence for the presence of biologically-generated methane in the Martian atmosphere.

Observations of methane in the Martian atmosphere have been reported since 1999, but they have always been conflicting. These measurements show highly variable methane concentrations, with global averages ranging from five to 33 parts per billion-volume.

Specifically, the discrepancy between measurements taken by NASA's Curiosity rover and the ExoMars Trace Gas Orbiter.

While Curiosity has detected methane in the Martian atmosphere, the ExoMars orbiter has not. This has sparked a heated debate within the scientific community.

Finding methanogens living below the surface of Mars would be strong evidence to suggest that the Red Planet's atmosphere does, in fact, contain methane at least partly generated by microbial processes. 

Methanogens produce methane as a by-product of their metabolism.  

Alternatively, atmospheric methane could stem from nonbiological processes such as volcanic or hydrothermal activity. Or, it could not exist at all. 

Though this debate is still far from settled, identifying locations where microbial life could exist on Mars brings scientists closer to understanding the true composition of the Red Planet's atmosphere and finding alien life.