MARTIAN LAVA TUBE CAVES AND MEGA-CAVES REVISITED

It has been proposed that lava tube cave passages in the lower gravity of Mars might attain much larger dimensions than those on Earth, perhaps as much as 500 m in diameter. Currently, our comparisons of terrestrial and Martian data do not support this idea. Utilizing roof plates and other features delineated by Greeley in 1970. review of orbital images of Mars has confirmed the presence of more than 100 collapsed lava tube caves on sections of Olympus Mons and Ascraeus Mons, many clearly visualized on Google Mars. Most are within the same size range as collapsed segments of similar features on Earth (maximum width about 105 m) although some are up to about 200 m wide. Using specially engineered svelte, rip-proof space suits, exploration between and below collapsed roof plates may reveal short segments of open cave. Further, one recent THEMIS image appears to show a row of skylights of what may be an open or filled lava tube cave or cave segments near Arsia Mons with similar dimensions. The idea that roof strength does not limit the diameter of such caves is supported by the 300 m span of the intact basaltic roof over a pit crater on the Atlantic island of Graciosa, far larger than the width of any known lava tube cave (about 35 m). Although the presence of hypothesized lava tube mega-caves has not been substantiated, intact segments of Martian lava tube caves of terrestrial size eventually may be candidates for geological and biological investigation.