When studying the molecules on planets and other celestial bodies in outer space, scientists don’t know what they’re going to find. So they need to send analytical instruments on rovers and other space vehicles that can handle samples of unknown composition. Mass spectrometers fit the bill. And because power is limited and equipment space is at a premium on satellites and rovers, any mass spectrometer along for the ride should be small. Mass spectrometers have been heading to Mars since the 1970s, when the Viking mission flew with an instrument containing an old-school magnetic-sector mass analyzer that could sort and separate ions over a range of mass-to-charge ratios (m/z) from 12 to 220. Miniature mass specs have come a long way since then. The Mars Organic Molecule Analyzer, or MOMA, will contain a miniature mass spec and will join a suite of other instruments on the European Space Agency’s ExoMars