Curiosity’s latest press release suggests early Mars was amenable to life. What’s the next step in determining whether life existed ? Let’s suppose microbial life was ubiquitous on early Mars; could a rover detect its remains or would we need a sample return mission ?
Curiosity has an impressive array of geological instruments, but doesn’t have the tools to detect (say) microscopic bacterial fossils embedded in a rock. Short of detecting something incredible like a sediment full of complex organic molecules, or fossils big enough to detect with the MAHLI(~1 mm in size), I don’t think Curiosity can find anything.
To detect microscopic fossils, you’d either need to return samples to Earth, or send a probe that can prepare and analyze samples with high power microscopes.
There was a discussion of this on NPR Science Friday (check their podcast archives) and apparently they have a detector for complex organic compounds that they could use to see if they are any.
Of course that doesn’t necessarily mean there was life there since they could have come from a non-living source, but if there was life you would expect to see them, so the absence of complex organics makes the existence of life much less likely.
Note that any life that was on Mars may have been there billions of years ago…
Bumped.
The Opportunity rover has now completed a Martian marathon - an amazing technological achievement: http://www.cnn.com/2015/03/25/world/opportunity-rover-marathon-milestone/index.html
What constitutes a Martian Marathon?
And the first guy to run it died. 
It managed to go 26 miles (and a bit, 26.2-something), the distance of a Marathon race, since it started roving.
They should make a race out of the distance that Opportunity ends up at when it finally joins Pheidippides (dies).
Thanks, engineer. I had no idea that was the distance.
A little rover trivia.
The Mars rover Opportunity was designed to compete a 90 day mission. Amazingly it is still functioning after more than 10 years.
Just read yesterday they now think Mars has enough nitrogen for life, which is good news for potential colonists and astro-archeologists.
Specifically, Curiosity found traces of nitrates (alkaline salts centered on a nitrogen atom) in a few locations on the Martian surface which could be a residue of life processes but can also be produced by non-organic sources. Nitrates are critical for both providing nitrogen (which provides the nitrogenous base for amino acids and glues together nucleotide sequences to form complex nucleic acids) and delivering other biologically critical metals and metallic compounds formed form phosphorous, potassium, calcium, and magnesium. Although life (our type of life, at least) is typically referred to as “carbon-based”, nitrogen is equally critical to all life as we know it. Most forms of life, however, are not capable of fixing free nitrogen from the atmosphere (where it is stable) and so it is produced by bacteria and a few types of plants and then concentrated through various means to serve as fertilizer.
The Curiosity rover contains a suite of instruments (the Sample Analysis at Mars (SAM) Instrument Suite, the Alpha Particle X-Ray Spectrometer (APXS), the Chemistry & Mineralogy X-Ray Diffraction (CheMin), and the remote Chemistry & Camera (ChemCam) instrument) to perform highly detailed chemical analysis specifically designed to look for indications of or precursors to organic molecules that would accompany life (again, as we know it). The capabilities of these instruments would be impressive on a lab on Earth; being packaged into a 900 kg self-mobile platform including power supply and communications is a feat of engineering rivaling ay other technical accomplishment of mankind to date. However, none of the instruments can actually image or sequence anything like a complex protein or nucleotide; what they are really looking for is the relative abundance of specific combinations of elements, or appearances of crystalline structures that would be indicative of residue from once living organisms. This is unlikely to be conclusive even if they found bacterial or other life, although it would be persuasive that the conditions and precursors for life could have existed on Mars at some point. (None but the most optimistic xenobiologists actually expects to find active life on the surface of Mars given the harshness of conditions and lack of liquid water; if life does still exist on Mars it will be buried well below the surface and likely powered by some unknown mechanism not driven either by direct solar impingement or hydrothermal sources that Earth life is sustained on.)
The purely scientific value of a sample return mission is arguable; while it would certainly provide a sample to more sophisticated analysis, the potential for contamination by Earth bacteria and organic constituents is problematic. The same is true, but moreso, for sending a crewed mission, as human beings are crawling with a vast multitude of bacteria, parasites, and biological molecules which would almost inevitably contaminate samples and the mission environment. (In situ sterilization procedures are unlikely to be completely effective as we’ve discovered organisms that manage to survive in dormancy even in the harsh vacuum, thermal, and radiation environment in open space.) We would have to be reliant on distinguishing indigenous forms of life from those brought with us, which is complicated by the suggestion (thought highly likely by many) that simple life could have been carried between Earth and Mars via meteor impact and ejecta earlier in planetary evolution when both planets had much thicker reducing atmospheres. The next rover mission, provisionally to land in 2020, would likely contain a more sophisticated suite of instruments based on what we find in observations from Curiosity, as well as the ability to bore deeper into the Marian soil to look for traces of liquid water, nitrates, and complex organic molecules.
Note that Mars is not the only, or even most likely location for life to exist in the Solar system. I personally favor Europa and Ganymede, where liquid water may exist below the frozen surface and energy provided by tidal friction with Jupiter and the other Galilean moons, but it has also been suggested that Callisto and even the volcanic Io could potentially contain life. Saturn’s moon Titan, with its thick organonitrogenous atmosphere and lakes of liquid methane could support some kind of life despite the bitterly cold temperatures that would make even the most robust Earth life come to a halt. It has also been suggested that microbial life could exist in the upper regions of the Venusian atmosphere, although the lack of water or another suitable solvent to act as a medium for form stable complex compounds makes that unlikely.
We also cannot completely discount some form of self-organizing, thermoregulating, reproducing system (which would at least meet the minimum criteria for what we consider to be “alive”) which is not at all based on organic molecules, although recognizing it as such would be a very difficult task as we could only speculate what it might look like or how it would self-organize.
Stranger
Instead of a sample return mission, could we realistically bring life there and see if it could survive? Not in the sense of releasing it, but using martian soil and bringing the other stuff that we assume mars had at one time (water, denser atmosphere, warmth) in a self contained environment with some seeds. Perhaps some contingency for something to exterminate that life after a certain time to prevent contamination.