"Recently discovered caves on Mars were created in a short amount of time by violent meteorite impacts and volcanoes, say researchers.This makes them very different from caves on Earth, which are made from slow dripping processes.The origin of Martian caves, identified earlier this year, are being discussed this week at a meeting of the Geological Society of America in Denver.Lava tubes, like those found near Earth's volcanoes, were recently identified on Mars by orbiting spacecraft. And ice melted by meteorite impacts could lead to bursts of cavern formation around the impact zone.Caves formed from both processes could 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," says cave researcher Associate Professor Penelope Boston of the New Mexico Institute of Mining and Technology.Caves, on the other hand, could be the ideal places to search for Martian life, she says.Meteorites and volcanoesMeteorite impacts could carve caves by creating two things vital for cave formation, Boston says."You have two ingredients happening as a result of impacts: fracturing and melting," she says.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 harbour microbial life.Lava tubes could also harbour 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 Assistant Professor 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."