Credit: NASA


Exploration of caves on planet Mars could potentially help shed light back on the history of past climate conditions on the Red Planet, as well as offer evidence for past microbial life.

Martian caves are protected from radiation and environmental extremes making them excellent preservers of potential biosignatures.

New research has looked into the promise of “ice caves” on Mars, rock-hosted caves containing ice. Ice-hosted caves are called “glacier caves”, and may be present on Mars as well.

Illustration of what an ice cave may look like on Mars. Hoarfrost grows on the ceiling and walls of a lava tube, with crystals growing in various directions. The cave is crumbling due to its old age. Some hoar crystals fell on the floor due to their own weight.
Credit: Norbert Schörghofer

The report – “Ice caves on Mars: Hoarfrost and microclimates” – is authored by Norbert Schörghofer of the Planetary Science Institute in Honolulu, Hawaii and Tucson, Arizona and appears in the journal Icarus.

Technologically feasible

“The exploration of caves on Mars is technologically feasible in the near-term,” Schörghofer explains.

“Drones that can operate in the tenuous Martian atmosphere are in active development. Autonomous drones that navigate in confined spaces are also being actively developed, as are all-terrain robotic vehicles and hoppers,” Schörghofer points out in his Icarus paper. “Miniaturized instruments that can be carried by small vehicles create science opportunities for the exploration of extraterrestrial caves. Further in the future, caves may serve as radiation-shielded habitats, and ice in the caves of the equatorial region would be a valuable resource.”

Planet Mars is believed to harbor many volcanic caves, observes Schörghofer. Skylight entrances and pit crater chains have been observed with cameras on several spacecraft circling Mars.

NASA Mars Reconnaissance Orbiter HiRISE image taken of an area on the lower southeastern flank of the volcano Elysium Mons. In the center is a small, dark pristine-appearing pit approximately 426 feet (130 meters) in diameter.
Credit: NASA/JPL-Caltech/Univ. of Arizona

Role of microclimates

Schörghofer points to a paucity of research on the topic, noting earlier work by another researcher that predicted, based on microclimate model calculations, that Martian lava tubes in the Tharsis and Elysium rises could have retained ice to the present day.

The new work assesses the role of microclimates and the physical structure of spelean (pertaining to a feature in a cave) ice formations expected in Martian caves. Some of the basic questions are: Where on Mars can caves be expected to contain ice? What do spelean ice formations look like on Mars?

Location of candidate caves in the Tharsis region on Mars.
Credit: USGS

“Martian caves are situated in environments where phase transitions of water are only by sublimation. The predominant type of cave ice is expected to be perennial hoarfrost that slowly grows in supersaturated cavities,” Schörghofer explains.

Caves on Mars are situated in a cold and dry environment (dry in terms of absolute humidity, not in terms of relative humidity), Schörghofer writes, “where phase transitions of water are presently only by sublimation. Cave ice formations are expected in the form of perennial hoarfrost sourced from the humid atmosphere. Where underground conduits and cavities are saturated with water vapor, hoarfrost crystals slowly grow over time.”

Work ahead

Schörghofer concludes that many aspects of ice caves on Mars remain to be explored, such as the growth of sublimation crystals around 200 K, fluid dynamics simulations of cave climates on Mars, consideration of relic cave ice, and analog studies of perennial hoarfrost in caves here on Earth.

“Finally, cave climates can be expected to play a larger role on bodies with a denser atmosphere, namely Venus and Titan,” Schörghofer concludes.

To gain access to the paper — “Ice caves on Mars: Hoarfrost and microclimates” – go to:

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