A planet just two stars down the road could potentially hold life, scientists say.
Barnard's Star is the second-closest system to our own, at just six light years away. A planet about three times the size of Earth and discovered just last year, Barnard b is just outside the habitable zone where liquid water can form overground - but a new paper has outlined a scenario under which life could emerge.
On the surface, Barnard b - as it's been dubbed - probably has a temperature of around -170degC. But underground it could be relatively balmy.
"Geothermal heating could support 'life zones' under its surface, akin to subsurface lakes found in Antarctica," said Edward Guinan, an astrophysicist at Villanova University in Pennsylvania.
Barnard b orbits Barnard's Star at about the same distance as Mercury orbits our sun - but Barnard's Star is a red dwarf - minuscule compared to the sun - and doesn't put out as much energy and heat.
"The two nearest star systems to the sun are now known to host planets," said Prof Guinan.
"This supports previous studies based on Kepler mission data, inferring that planets can be very common throughout the galaxy, even numbering in the tens of billions," added fellow Villanova University academic Scott Engle.
"Also, Barnard's Star is about twice as old as the sun - about 9 billion years old compared to 4.6 billion years for the sun. The universe has been producing Earth-size planets far longer than we, or even the sun itself, have existed."
Many scientists believe life may have started out on Earth under the sea near thermal vents.
If travelling six light years remains out-of-reach for the foreseeable future, Jupiter's moon Europa could be a better place to start looking for alien life underground.
"We note that the surface temperature on Jupiter's icy moon Europa is similar to Barnard b but, because of tidal heating, Europa probably has liquid oceans under its icy surface," said Prof Guinan.