|MadSci Network: Astronomy|
I'll begin by telling you a little bit about Mars. Mars is cold. During several months of the Martian year, the temperatures do not go over freezing anywhere on the planet. The average temperature is -81 degrees Fahrenheit with a high of 68 F and a low of -220 F. That would indicate that any microbes on Mars need to be adapted for the cold. Temperature differences from night to day are over 150 F so any microbes on Mars would have to cope with wide temperature variations unless they were beneath the surface where the temperature is more constant.
Also, the atmospheric pressure is much lower than on Earth (about 1--2 hundredths the pressure on Earth). The atmosphere is composed of carbon dioxide (95.33%), nitrogen (2.7%), Argon (1.6%), oxygen (0.13%), water (0.03%) and neon (0.00025%). The amount of water is only 1/1000 as much as on Earth but can form patches of fog in the morning in some valleys. The very low amount of oxygen tells us that any microbes on Mars are probably anaerobic (meaning they don't need oxygen to survive). Also, there is no protective ozone layer in the Martian atmosphere, so the Sun's UV light penetrates to the surface. UV light can break apart organic molecules, including DNA, so any surface bacteria would have to be very tolerant of high radiation.
Liquid water is a must for life as we know it. Mars has no standing liquid water on its surface. There may be liquid water beneath the surface which is salty (to lower the freezing temperature, otherwise all the water on Mars would be frozen).
All this information tells us that any subsurface bacteria would have to survive in salty water (these are called halophilic) and any surface bacteria would have to be tolerant to radiation and to very dry conditions (these are called xerophytes). All microbes that would survive on Mars cannot require oxygen and must be adapted to cold conditions.
There is a bacteria (Streptococcus mitis) which survived a trip to the Moon where it was exposed to vacuum, extremely cold temperatures, no nutrients or water, and no radiation protection (see Earth Microbes on the Moon for an article). After 2.6 years, the bacteria could revive itself. There are bacteria on Earth in the Columbia River basalts which are called SLIMEs (Subsurface LIthoautotrophic Microbial Ecosystem) and live about 3 miles beneath the surface and survive by using a little bit of water and crushed rock. Perhaps a similar organism could exist on Mars.
For more info on Mars and life on Mars, check out the following web sites:
Views of the Solar System for information about the planets;
Life in Extreme Environments for information on extremophiles---bacteria that live in extreme environments on Earth. There are a lot of links to other sites that can give a lot of information on bacteria in extreme environments.
NASA's Life from Mars site.
There has also been a lot of discussion on the possibility of life on Europa, which may have a cold ocean of water underneath its icy crust. Check out this article discussing the possibility of life on Europa.
Try the links in the MadSci Library for more information on Astronomy.