Simply put, today’s announcement from NASA that methane detected in the atmosphere of Mars is either of geologic or biological origins. These observations have been confirmed by orbiting spacecraft and from land and space based telescopes around Earth. The only step left is confirmation from the surface not only that the methane is being produced but what exactly is causing it. The Mars Science Laboratory which will be launched in 2011 will carry with it the capability to detect methane gas and its landing site should take this into consideration.
However, in doing a little bit of research, one of the sites of interest that the MSL team has already discounted is one of the sites now affiliated with increased concentrations of methane gas. It would be my hope, and the hope of other Mars enthusiasts, that they take a look at the site again. The site I’m referring to is Nili Fossae, and it perhaps holds one of the best possibilities for finding evidence for past or present microbial life on Mars. NASA also mentioned that the much broader regions of Arabia Terra and Syrtis Major are also affiliated with these higher methane readings.
In taking a look at my nifty Mars wall map in my dorm room, I quickly realized that Arabia Terra and Syrtis Major are not only next to each other, but Nili Fossae is a smaller site on the eastern extent of Syrtis. To those out there who might not be familiar with Martian geography, I’ve included a map of the region for clarity. Arabia Terra and Syrtis Major straddle the equator, but are predominantly in the Northern Hemisphere of Mars.
The above image has (from left to right) Arabia Terra, Syrtis Major, and Nili Fossae to the north and eastern edge of Syrtis. 
A full image of Mars puts their location into perspective. Syrtis Major is the dark feature near the center of Mars and on the right-hand limb with Arabia Terra being the light colored region to the left. The eastern extent of Valles Marineris would be barely visible on the far left-hand limb and along the equator of the planet in this image.
Why do I mention their location? For one, everything significant we know about Martian geological activity is on the other side of the planet from these regions, which includes: the Valles Marineris, the largest canyon in the solar system, not just dwarfing the Grand Canyon but blowing it out of the water. Valles Marineris is as long as the United States and so wide and deep in locations, its possible to not see the other side or the bottom. The theory is that it was formed as a result of something similar to plate tectonics, and is therefore a massive fault-line. Then there is the “Tharsis Bulge.” The Tharsis region of Mars is very noteworthy for its apparent geologic activity, notably its four large volcanoes, all of which dwarf their Earth counterparts and one in particular, Olympus Mons, is the largest mountain in the solar system, being nearly four times higher from base to top than Mount Everest.
That being said, there is sparse physical evidence elsewhere on Mars based on orbital observations that is indicative of any other significant geologic activity, with the exception of a volcano a few thousand miles east of Syrtis Major, about the same distance as the Valles Marineris is west from Arabia Terra. Aside from some volcanic debris in the region, it remains highly likely, but not impossible, that there is no geological activity in this region. The only way to know for sure if these increased levels of methane are biological or geological is to go there. My argument, based on geography here, is that it is very, very possible that the methane is being produce by microbes. If it were a geologic process, over a decade of constant observation from remote sensing satellites orbiting the planet, we should have detected something by now. The fact that these subtly higher levels of methane were only detected from orbit in 2003 and little has been observed since from Martian orbit supports my conclusion.
Nili Fossae - the light colored pink areas indicate concentrations of clay in this image. The blue is suspected to be volcanic material.
Getting back to Nili Fossae, it’s peaked some scientific interest in recent years aside from being near the epicenter of the increased methane content in the atmosphere. It boasts one of the largest concentrations of clay materials on the planet. With Phoenix’s discovery of water ice below the surface in the northern polar region, it’s conceivable that the clay material could have enough water content to support small forms of life deep beneath the surface of Mars. While MSL will not be equipped with the tools necessary to directly observe that life, it can confirm where the methane gas is coming from and determine if it is biologic in origin.
Obviously, I’m leaning towards the exploration of this region for the prospects of finding life there. But isn’t that what every Mars mission has been centered around? The Viking landers in the 1970’s went out to directly look for life, Pathfinder was a proof of concept mission for later missions, Spirit and Opportunity (still chugging away after 5 years!) went in search of finding evidence of past or present water on Mars, the Phoenix lander was looking for evidence of subsurface water ice, and the failed Beagle 2 mission in 2003 would have dug into the surface looking for evidence of microbes. Mars Science Lab has the same objective, continuing the search for life on the Red Planet.
It would be foolish to disregard this region, especially with the new information that has become available. If not the MSL mission, then perhaps Nili Fossae will be left for another future spacecraft to explore.