Volcanic caves hidden on the Moon
The early millennia on the Moon featured volcanic eruptions and magma oceans. As various lava flows ended and their exteriors cooled, the warmer inside core often kept flowing out. This formed lava tubes under the lunar surface – similar to the narrow lava tubes found near Earth’s volcanoes but hundreds of feet wide. These volcanic caves may be so common on the Moon that they have an area equivalent to West Virginia, according to one estimate.
The winding rilles (narrow valleys) found on the Moon are thought to be collapsed lava tubes. Gaps in the path of these rilles may be the uncollapsed portions of lava tubes. However, orbiting probes have been unable to find any entrances to these uncollapsed portions.
Instead, the orbital cameras have identified three “skylights” that seem to lead down into volcanic caves. Two are on the near side, and one is on the more difficult to visit far side. Astrobotic is targeting a near-side skylight in the Marius Hills (on the left half of the near side, a little above the equator). This pit is about 50 yards wide and 35 yards deep. The Lunar Reconnaissance Orbiter has snapped four images of this skylight, including a sideways peek that appears to confirm the existence of a passageway under the surface.
When Astrobotic visits the Marius Hills skylight, its lander will fly directly over the opening to begin building a 3D model using its navigation instruments (cameras and LIDAR). Then its rover will circle the pit, peering in at intervals to get more detailed mapping of the sides and floor. With sufficient funding, the expedition also will release a micro rover able to descend into the pit. The micro rover could rappel over the side on a high-strength cable, or it could be sufficiently hardened to simply dive over the edge. The 35-yard fall in one-sixth gravity might be survivable.
