A weird hole on Mars has been discovered — the 35 meter opening is very strange and there doesn’t appear to be a logical explanation. The hole in the middle of a depression (crater) appears to have a opening (cave) about 20 meters deep.
What created this unusual hole in Mars? The hole was discovered by chance on images of the dusty slopes of Mars’ Pavonis Mons volcano taken by the HiRISE instrument aboard the robotic Mars Reconnaissance Orbiter currently circling Mars. The hole appears to be an opening to an underground cavern, partly illuminated on the image right. Analysis of this and follow-up images revealed the opening to be about 35 meters across, while 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. 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.
Source: A Hole in Mars (Astronomy Picture of the Day)
Earlier this year, the CTX camera team saw a crater containing a dark spot on the dusty slopes of the Pavonis Mons volcano … The dark spot turned out to be a “skylight,” an opening to an underground cavern, that is 35 meters (115 feet) across. Caves often form in volcanic regions like this when lava flows solidify on top, but keep flowing underneath their solid crust. These, now underground, rivers of lava can then drain away leaving the tube they flowed through empty. We can use the shadow cast on the floor of the pit to calculate that it is about 20 meters (65 feet) deep.
Source: Caves and CratersUpdate: 24th July 2012
Just found an earlier image of the cave/opening. California 7th graders discovered this Martian pit feature at the center of the superimposed red square in this image while participating in a program that enables students to use the camera on NASA’s Mars Odyssey orbiter. The feature, on the slope of an equatorial volcano named Pavonis Mons, appears to be a skylight in an underground lava tube. Full Story.