ESA’s Mars Express has discovered a series of 'pit-chains' in the Tharsis region of Mars that could, says ESA, be tempting targets in the search for microbial life.
Sitting on the flanks of one of the largest volcanoes in the solar system, Tharsis Montes, the pit-chains are a series of circular depressions that formed along fracture points in the Martian crust.
Pit-chains, also found on the Earth and moon, are created when lava streaming from a volcano solidifies on the surface, leaving a molten tube of lava running below.
Once volcanic activity ceases, the tube empties, leaving behind an underground cavity. Eventually, the roof over the cavity can collapse, leaving circular holes.
They can also be caused by tension in the Martian crust, which causes parallel elongated depressions known as grabens, in which pits can form.
Often, though, such pits are caused by water, forming when the surface limestone rocks collapse, exposing the groundwater underneath.
And this is why ESA scientists are excited. If there are any cave-like structures associated with the pits, microorganisms could have survived, protected from the harsh surface environment.
They could also provide an environment for people, says ESA. While surface radiation on Mars is around 250 times higher than that found on the Earth, caves could provide a refuge.