Carol Stoker and Suzanne Young just presented a pair of presentation on the habitability of Mars. Bottomline: The Mars Phoenix Landing Site is capable of supporting life today.
The also calculated a habitability index for the various sites landers have explored on Mars. If a site has a probability of supporting life greater than 50%, it is considered reasonable to go looking for life using dedicated experiments.
To calculate the Habitability Index, they create something similar to the Drake Equation. Here, the habitability index is the product of the probability that liquid water has been present, the probability of a biologically abailable energy source, the probability that chemical building blocks available, and the probability that the environment is benign and nontoxic.
The problem is there is no way to assign an absolute value for any factor. The best that can be done is to make an educated guess from multiple approaches and to compare sites that do not have similar measurement types. This gets really complicated when direct measurements of each of the probabilities isn’t actually made and theory must be invoked (for instance, Phoenix didn’t get all the needed data). Additionally, data that does exist often has more than one interpretation.
All that said, let’s consider the situation at the Mars Phoenix site:
Liquid Water – Evidence: segregated ice, macroscopic evidence for melting at some time. Additionally the volume fraction of ice in soil exceeds what the pore space would allow via vapor deposition, and minerals that can only form in liquid water are present (eg carbonates at 5% level).
Energy: Solar and chemical energies are both good, but there is a need for shielding from UV for life to use solar energy (It’s a bit destructive to organics). Shielding in the form of transparent glassy grains that block UV and admit other wavelengths were found, and this offers a chance for tiny hiding life. Also, on Earth perchlorate is metabolized by many chemoautotrophs and could be chemical source for life on Mars as well.
Chemistry: The presence of Carbon, Oxygen, Nitrogen, Hydrogen, Phosphorus, and Sulfer are all thought to be needed. At this stage C and O are known to exist, but we’re not sure Nitrogen is there – can’t get a reading on nitrate with lots of percholorate around. Phosphorus also was not seen with Phoenix’s wet chemistry lab, but it couldn’t have been seen with the WCL setup. Sulfer is possible; the data is still work being worked on and early results are ambiguous. While not everything we’d like to see were there, many biologically interesting Ions were located (Na+, K+ Ca+ Mg2+ Cl- C004-).
Benign and NonToxic: They found the pH levels are non stressful, and the environment contained no poisens. All is good.
Put together, they feel that at the pole, there is the highest value for the habitability index- searching for life justified.
NOTE – this value is for now and it is hapitable *today.*
Kind of cool. Yes?