14 DAY TRIAL // After water, Mars comes with other surprises, too.
Images from Nasa's Odyssey spacecraft, launched in April 2001 to hunt for past or present water on Mars, have revealed to astronomers what could be seven caves on the Red Planet's surface.
The potential caves are located on the flanks of the Arsia Mons volcano and are deep enough that their floors cannot be watched through the opening.
Mars Odyssey's Themis instrument, employing visible and infrared radiation to measure the temperature properties of the Martian surface, just enhances the idea.
This discovery has a crucial importance, as the caves are regarded as the only natural structures capable of offering safety for primitive life forms from micrometeoroids and solar and cosmic radiations that bombard the planet's surface.
The spacecraft detected what could be vertical "skylight" entrances to caves, 100m and 252m wide (330-828ft), below the surface with sheer drop of 80-130m (270-430 ft) or more to the cave floors below.
In the daytime, one of the possible caves, dubbed "Annie", is warmer than its neighboring pits and cooler than sun warmed zones, while during the night time, it spreads more heat than almost all close by areas.
"This was exactly what would be expected if the feature were a cave. Nothing like these features has been seen elsewhere on Mars," said co-author Glen Cushing, from the US Geological Survey in Flagstaff, Arizona.
The "sister caves" have already received names: Dena, Chloe, Wendy, Annie, Abbey, Nicki and Jeanne.
The researchers estimated the minimum depths of the caves to extend between 73 to 96m (240-315ft) below the surface, even if their floors cannot be seen except Dena, which was estimated to extend 130m (426ft) below the surface.