An Astrobiology Field Laboratory (AFL) is under consideration that would conduct a robotic search for life. It would be the first mission since Viking in the 1970s to look specifically for evidence of past or present life. The robotic lab would carry instruments for identifying and measuring the chemical building blocks for life (as we know it), including thousands of carbon-carrying compounds, elements such as sulfur and nitrogen, and oxidation states of trace metals associated with life. It would conduct detailed analysis of geologic environments identified by the 2009 Mars Science Laboratory as being conducive to life. Such environments might include fine-grained sedimentary layers, hot spring mineral deposits, icy layers near the poles, or sites such as gullies where liquid water once flowed or may continue to seep into soils from melting ice packs.

When could AFL fly to Mars? Sometime around 2013 is a possibility. The Mars program is "discovery-driven" - that is, NASA tries to keep it's options open so as to follow up on new discoveries. Keeping the program flexible means that a proposed mission like AFL is simply an option. The next few Mars missions could make discoveries that would be so fantastic that it's better not to be "locked in" as to what kind of mission and science instruments to send. But on the other hand we can't wait too long to start developing complex future missions so they're being studied now in case they're needed.