Meanwhile, the southern half of the Martian surface is rough and heavily cratered, and about 2.5 miles to 5 miles (4 km to 8 km) higher in elevation than the northern basin. Recent evidence suggests the vast disparity seen between the northern and southern halves of the planet was caused by a giant space rock smacking into Mars long ago.
Still, there are ways to produce methane without life, such as volcanic activity. ESA's ExoMars spacecraft planned for launch in 2016 will study the chemical composition of Mars' atmosphere to learn more about this methane.
However, current models of early Mars' climate cannot explain how such warm temperatures could have existed, as the sun was much weaker back then, leading some to ask whether these features might have been created by winds or other mechanisms. Still, there is evidence suggesting that ancient Mars was warm enough to support liquid water in at least one site on its surface. Other findings hint that ancient Mars was once cold and wet, not cold and dry nor warm and wet, as is often argued.
The surface of Mars is very hostile to life as we know it, in terms of cold, radiation, hyper-aridity and other factors. Still, there are numerous examples of life surviving in extreme environments on Earth, such as the cold, dry soils of the Antarctic Dry Valleys and the hyper-arid Atacama Desert in Chile.
There is life virtually wherever there is liquid water on Earth, and the possibility that there were once oceans on Mars leads many to wonder if life ever evolved on Mars and, if so, whether it might be extant. Answering these questions might help shed light on how common life may or may not be in the rest of the universe.
NASA's plan as of 1969 was to have a human Mars mission by 1981 and a permanent Mars base in 1988. However, interplanetary human voyages pose definite scientific and technological challenges. One would have to deal with the rigors of travel — issues of food, water and oxygen, the deleterious effects of microgravity, potential hazards such as fire and radiation and the fact that any such astronauts would be millions of miles away from help and confined together for years at a time. Landing, working, living on another planet and returning from it would offer a host of challenges as well.
Nevertheless, astronauts seem eager to find out. For example, this year six volunteers lived in a pretend spacecraft for nearly a year and a half in the so-called Mars500 project, the longest spaceflight simulation ever conducted, aimed at replicating a manned mission to Mars from beginning to end. There are even numerous volunteers for a one-way trip to the Red Planet. Tiny rock-eating microbes could mine precious extraterrestrial resources from Mars and pave the way for the first human colonists, and farmers could grow crops on its surface. The mystery as to whether or not humans will ever go to Mars may rest largely on whether or not the powers-that-be can be convinced to go there.