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How does the Curiosity rover analyse Mars' rocks to find signs of life?

Is it only based on life-supporting chemicals, or is there more involved?

What specific tests are performed? We recall the Viking labeled release experiments that caused so much controversy.

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It doesn't, not directly at least (it doesn't have a single microscope or anything like it), unless something large enough waves back to us and one of its cams catches that memorable moment. But it could, in theory, infer that there is some biology present. For example, it has five spectrometers (Wikipedia says four, but I count five):

  • ChemCam that includes an optical emissions spectrometer (Laser-Induced Breakdown Spectroscopy, or LIBS) that basically blasts rocks and soil with a laser and a high-resolution telescope camera (Remote Micro Imager or RMI) then spectrally analyzes composition of vapors.
  • APXS (Alpha Particle X-ray Spectrometer) analyzing chemical composition by irradiating samples and then measuring scattered alpha particles and X-rays. It's part of the science package on MSL's robotic arm.
  • CheMin (Chemistry and Mineralogy) analyzing microcrystalline (read: powdered) mineral samples for structural characterization of materials using X-rays.
  • QMS (Quadrupole Mass Spectrometer), part of its Sample Analysis at Mars (SAM), that samples ions by filtering them based on their charge and mass.
  • Tunable Laser Spectrometer (TLS), also part of SAM, analyzing atmosphere of Mars in an otherwise similar fashion to ChemCam's LIBS + RMI.

And it also has a gas chromatograph (also part of SAM) and a long list of other cameras, including one (MAHLI - Mars Hand Lens Imager ) on its robotic arm, on its mast (MastCam), and so on.

So it packs plenty of instruments to analyze elemental composition of pulverized or gaseous samples, with contact or remotely (ChemCam), but, for example, if you placed a vial filled with amoeba next to it, it couldn't tell you that it has life in it unless you gave it enough time to detect chemical, electrical, or otherwise physical change in metabolites. Assuming the sample was alive, and kept so during the analysis, of course.

And this brings me to the point I'm trying to make; MSL (Mars Science Laboratory, aka the Curiosity rover) isn't equipped to detect life. It's not its purpose, that will be tasks for Mars 2020 (NASA) and ExoMars (ESA) rovers that are scheduled to launch in 2020 and 2018, respectively. MSL's purpose is to search for conditions for life as we know it.

It could, theoretically, infer presence of life by detecting metabolites, or life's past existence, say, by chemically analyzing fossilized sediments, perhaps in clay deposits, but we've had no such luck yet. And if we did, it would most likely not be considered an indisputable proof either, considering that MSL lacks quite a bit of instrumentation to disqualify all other possible rational explanations for its findings.

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