How does a space probe identify molecules without actually obtaining the molecules? The common identification techniques I can think of are spectroscopy and magnetic resonance, but for both of them, the apparatus needs to interact with the molecule and get readings from them (first the absorption and then the transmission/emission), which, from thousands of kilometers away, sounds quite difficult.

Is there a completely different technique developed for space? Or does space spectroscopy or magnetic resonance work a bit differently than in earth?

  • $\begingroup$ Are you thinking of any particular space probes and their associated instrumentation? Otherwise, it might be a bit general, list type question, no offence. $\endgroup$
    – user81619
    Oct 31, 2015 at 0:18
  • $\begingroup$ If you're thinking of Mars explorers, their arsenal of on-board chemical analysis should be googlable. $\endgroup$
    – Gert
    Oct 31, 2015 at 0:19
  • $\begingroup$ I just thought of this after reading how New Horizons found water on Pluto. But the question addresses all spacecraft that are capable of identifying molecules on a celestial body without landing on it. A similar question on the site led me to this page: nasa.gov/mission_pages/spitzer/multimedia/pia13287a.html $\endgroup$
    – Esoppant
    Oct 31, 2015 at 0:22
  • $\begingroup$ Same with Clementine, water on the moon, en.m.wikipedia.org/wiki/Clementine_(spacecraft) I am no expert, but I can't immediately see why space setup should be any different in principle. Possibly more protection from radiation skewing the results would be needed but that's just my guess. Physics is physics, no matter where you are. $\endgroup$
    – user81619
    Oct 31, 2015 at 0:25
  • $\begingroup$ Apparently, infrared telescopes can gather light from the molecules they want to identify; but I'm still a bit curious about how they manage to gather light only from specific molecules from such a distance. Wouldn't background radiation affect the process greatly? $\endgroup$
    – Esoppant
    Oct 31, 2015 at 0:29

1 Answer 1


There are several broadband light sources in outer space such as quasars and blazars which basically can act as a light bulb. Earth bound telescopes as well as satellite telescopes can see absorption features in the light when the light passes through some cloud in outer space that contains molecules before the light reaches earth. In addition molecules in outer space can be excited by this radiation or by collisions with other molecules and emit light. In fact there are many masers in space such as water masers and methanol masers.


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