FIRST OBSERVED ENTRANCES INTO MARTIAN TUBULAR CAVES

The first windows into extraterrestrial tunnels (formed either as volcanic lava tubes or subsurface tectonic fractures) may have been identified in the Tharsis Montes region of Mars. These candidate entrances are collapse features that occur intermittently along several laterally continuous structures that can be straight, curvilinear, branched or braided, and were identified in images acquired by the Mars Odyssey Thermal Emission Imaging System Visible-wavelength camera, and by the Mars Reconnaissance Orbiter Context camera. With diameters up to ~50 m and depths that exceed 20 m at some locations, these candidate cave entrances are intermediate in size compared with terrestrial pit craters, and somewhat larger than terrestrial lava-tube skylights. The tunnels that accommodate these entrances are up to 65 m across in some places and show clear surface expression in segments ranging from ~5 km to over 100 km in length. Although we cannot determine the unobstructed lateral subsurface extents of these tunnels, they may be analogous to a number of terrestrial structures that continue unimpeded for many kilometers.

With a very thin atmosphere and virtually no magnetic field, Mars is constantly exposed to micrometeoroid impacts, solar flares, UV radiation, high-energy cosmic radiation, intense dust storms and extreme temperature variations—which cumulatively render the surface completely inhospitable to organic material. Accordingly, caves are important to the future of Mars exploration because they offer effective protection from these hazards and may someday become vital in-situ resources by providing humans with temporary (or even permanent) shelters that must otherwise be manufactured (and then transported) or constructed in place. Cave environments are also important to astrobiology investigations because they are among the only accessible environments capable of preserving evidence of past or present microbial life (if such ever existed on Mars).

At least 7 different examples with multiple candidate entrances were identified in a limited sample area, so we expect that many more exist in other volcanic regions across Mars. As more cave entrances become known and examined more closely, new categories of exploration technology will be developed and caves will become increasingly important targets for planetary exploration.