This made me go "huh, then how do they know their sensor is working at all?" The answer is that the sensors are two spectrometers that detect all sorts of gase

This made me go "huh, then how do they know their sensor is working at all?" The answer is that the sensors are two spectrometers that detect all sorts of gases, not just methane: [0] https://en.wikipedia.org/wiki/Nadir_and_Occultation_for_Mars_Discovery https://en.wikipedia.org/wiki/Nadir_and_Occultation_for_Mars... [1] https://en.wikipedia.org/wiki/Atmospheric_Chemistry_Suite https://en.wikipedia.org/wiki/Atmospheric_Chemistry_Suite