Caves spotted on Mars : Dark 'skylights' could be openings to Martian shelters.
The headline writer in Nature seems to have missed the point. The article refers not to little green men, but to the possiblity that these 'caves' might be places where water ice might collect - a necessary starting point for the generation of primitive 'life forms'.
If I were a betting man I might wager that this will all come to nothing, just like all the previous sightings of life on Mars. Still if you get a chance, do watch the TV program that I referred to earlier.