Human visitors to Mars need somewhere to shelter from the radiation, temperature swings, and dust storms that plague the planet.
If the planet is anything like Earth or the moon, it may have large underground lava tubes that could house shelters. Collapsed sections of lava tubes, called skylights, could provide access to these subterranean refuges.
Several pits in the Arsia Mons region may be collapsed skylights or openings into subterranean lava tubes.
However, there is much uncertainty. An image of one of them shows an illuminated sidewall, which could indicate that it's just a cylindrical pit.
The hole in the featured image could only be a pit or shaft and not an entrance to a cave or lava tube. They're found on Hawaiian volcanos, where they're called pit craters.
They don't connect to long caves or lava tubes. They're the result of a collapse that happened much deeper underground.
In Hawaii, the pit craters range from 6 to 186 m (20 to 610 feet) deep and from 8 to 1140 m (26 to 3,740 feet) wide. The Arsia Mons pit in the leading image is only about 178 m (584 feet) deep.
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