NASA's Mars Reconnaissance Orbiter took this photo of a cave skylight on the southeastern flank of Pavonis Mons, a large volcano in Mars' Tharsis Region. The pit is about 180 meters wide.
This photo by NASA's Mars Reconnaissance Orbiter shows a cave skylight roughly 35 meters across and 20 meters deep. Caves often form in volcanic regions when lava flows solidify on top, but keep flowing underneath their solid crust. The origin of the larger hole containing the skylight is unknown.
These six excerpts of images taken by NASA's Mars Odyssey spacecraft show seven openings in the Martian ground on the north slope of the volcano Arsia Mons, which is located at 9 degrees south latitude, 239 degrees east longitude. The holes range in diameter from about 100 meters to about 225 meters.
This feature on Mars is a candidate cavern entrance. It is northeast of Arsia Mons, one of the four giant Tharsis volcanoes on the red planet.
A possible opening to a subsurface cave system on Mars. Scientists say these structures could be a possible safe haven for Mars-bound astronauts. They could also preserve any evidence of potential Martian life.
NASA's Mars Reconnaissance Orbiter photographed this hole, which is on the slopes of the giant Martian volcano Arsia Mons. The hole is about the size of a football field and is so deep that it is completely unilluminated by the sun.
NASA's Mars Reconnaissance Orbiter snapped this shot of a trough running down the center of a valley in the Tartarus Colles region of Mars. Scientists think the structure originally formed as a lava tube.
This image from NASA's Mars Global Surveyor spacecraft shows some of the lava flows near the summit of the Martian volcano Ascraeus Mons. The discontinuous channel running across the upper half of the image is a collapsed lava tube.
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.