If Mars looks like a primordial Earth-on-ice, the similarity ends just below the surface where Martian caves are borne not of slow dripping processes but from brief, intensely violent times, say researchers.

©NASA/JPL-Caltech/ASU/USGS
This image from the Mars Odyssey orbiter, shows a patch of Martian ground, centered on a possible cave skylight informally called "Annie," which has a diameter about double the length of a football field.


It's meteor impacts and volcanoes which are thought to make Martian caves. Lava tubes, like those found near Earth's volcanoes, have been recently identified from Mars orbiting spacecraft. While melted ice by meteor impacts may create all the ingredients for bursts of cavern formation around the impact zone.

Both types of caves offer one very attractive feature to prospective Martian life that the Martian surface lacks - - protection from the barely filtered solar and cosmic radiation that bombards Mars' surface.

"My estimate of how likely it will be to find life or evidence of life lying on the surface is vanishingly small," said cave researcher Penelope Boston of the New Mexico Institute of Mining and Technology (New Mexico Tech).

Caves, on the other hand, could be the ideal places to search for Martian life, she said.

Both types of Martian caves are the topics of presentations on Oct. 29th and 31st at the meeting of the Geological Society of America in Denver.

Meteor impacts could carve caves by creating two things vital for cave formation, Boston told Discovery News.

"You have two ingredients happening as a result of impacts: fracturing and melting," said Boston.

On Earth it's along fractures and planes in rocks that caverns form. Waters travel through the fractures and dissolve and widen them if they are the right type of rock.

On Earth the right kinds of rock are carbonates, like limestone, or evaporites, like salts and gypsum. Both types of rock are readily dissolved by either mildly acidic or neutral water. Carbonates are not known to exist on Mars, but evaporites are thought to be plentiful. All such caves on Earth harbor microbial life.

Lava tubes could also harbor signs of life, or at least clues to past Martian climates.

"Our work in Hawaiian caves has shown an abundance of microbial growth as biofilms and mats on cave surfaces," reports Datta Saugata of Georgia College and State University.

The Hawaiian lava cave microbes are particularly fond of those minerals in the caves which are made of rocks that have weathered away by water. So if there were ever watery times on Mars, lava caves would probably have evidence of them, plus signs of any past life.