Nasa scientists are baffled as to what - or maybe even who? - created this unusual hole on the surface of Mars.
The hole was discovered by chance on images of the dusty slopes of the Red Planet's Pavonis Mons volcano. It appears to be an opening to an underground cavern, partly illuminated to the right of the opening.
© NASA
A hole in Mars: The opening was discovered by chance on images of the dusty slopes of the Red Planet's Pavonis Mons volcano

The interior shadow angle indicates that the underlying cavern is roughly 20 meters deep.Why there is a circular crater surrounding this hole remains a topic of speculation, as is the full extent of the underlying cavern.

© NASA
Pavonis Mons (bottom centre) is located at the southern edge of the Tharsis quadrangle of volcanoes. The Tharsis Montes volcanoes lie along the crest of a north-east trending rise - or Tharsis bulge - that extends more than 3,000 km across the western equatorial region of Mars
Holes such as this are of particular interest because their interior caves are relatively protected from the harsh surface of Mars, making them relatively good candidates to contain Martian life. These pits are therefore prime targets for possible future spacecraft, robots, and even human interplanetary explorers.

The images were taken by the HiRISE instrument aboard the robotic Mars Reconnaissance Orbiter currently circling Mars.