Martian lava tube

Martian lava tubes are natural sub-surface lava tube caverns on Mars that are believed to form as a result of fast-moving, basaltic lava flows associated with shield volcanism. Lava tubes usually form when the external surface of the lava channels cools more quickly and forms a hardened crust over subsurface lava flows. The flow eventually ceases and drains out of the tube, leaving a conduit-shaped void space which is usually several meters below the surface. Lava tubes are typically associated with extremely fluid pahoehoe lava. Gravity on Mars is about 38% that of Earth's, allowing Martian lava tubes to be much larger in comparison.

Lava tubes and related flow structures were first recognized upon examination of Viking orbiter images, and later identified using orbiter imagery from Mars Odyssey, Mars Global Surveyor, Mars Express, and Mars Reconnaissance Orbiter. Lava tubes can visually be detected two ways. The first is as long sinuous troughs known as rilles, which are believed to be the remains of collapsed lava tubes. The second method of possible identification is through observation of cave "skylights" or pit craters, which appear as dark, nearly circular features on the surface of Mars. In June, 2010, a group of seventh grade science students at Evergreen Middle School in Cottonwood, California, participating in the Mars Student Imaging Project, helped researchers discover a new series of lava tubes near Pavonis Mons through identification of a skylight estimated to be 190×160 meters wide and at least 115 meters deep. It is only the second skylight known to be associated with this volcano. In addition to orbital imagery, lava tubes could be detected through the use of:

There has been increased interest in the identification and investigation of lava tubes because it could present scientists with information regarding the geological, paleohydrological, and supposed biological histories of the planet. When speaking about lunar lava tubes, Dr. William "Red" Whittaker, CEO of Astrobotic Technology, states that "something so unique about the lava tubes is that they are the one destination that combines the trifecta of science, exploration, and resources." Access to uncollapsed sections of lava tubes can be done by entering at the end of rille, through skylights, or, possibly, by drilling or blasting through the roof of a lava tube. Initial exploration of lava tubes will most likely involve rovers, but many challenges will be presented. Traditional skylights have large rubble piles directly below them (as seen in the first figure) which could become an extreme obstacle for the rover to overcome. The large vertical drop that the rover would have to perform would also have to be taken into consideration, as well as the ability of the rover to remain in communication with assets at the surface or in orbit. Lack of sunlight could also be problem if the rover's main power source is solar energy.

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