Aliens may have once lived miles beneath the surface of Mars, research suggests.
Scientists say life on the Red Planet is likely to have emerged deep underground as tons of thick ice melted.
It would have been up to 4 billion years ago when the sun was about 25 percent dimmer than now.
NASA’s Perseverance robot, due to land in February, has instruments for collecting rock samples only up to 30 feet deep.
If the findings are correct, the space agency will “need a bigger drill” for its Mars missions.
Single-cell organisms began thriving on Earth when it was much colder than now, possibly due to insulating gases or magnetic solar storms providing some heat.
The same may have happened on Mars — with radioactive decay causing warmth to melt the bottom of the ice into lakes of water deep below the surface.
Dr. Lujendra Ojha of Rutgers University said: “At such depths, life could have been sustained by hydrothermal activity and rock-water reactions.
“The subsurface may represent the longest-lived habitable environment on Mars.”