The 2001 Mars Odyssey mission makes use of many innovative technologies, but the most important among them are the three instrument packages. All three involve the use of spectrometers.
2001 Mars Odyssey makes use of several kinds of spectrometers:
Spectrometers are instruments that allow scientists to collect data that would otherwise be invisible to us. Our eyes are sophisticated detectors that can reveal much of the world around us, but they are only sensitive to a very small part of the electromagnetic spectrum that characterizes light.
We call the part of the electromagnetic spectrum that we can see "visible" or "optical" light. To fully appreciate the complexity of the world around us, however, we need to rely on human-made devices to provide views of the "invisible" world -- that is, the parts of the electromagnetic spectrum we cannot see without the aid of technology: gamma rays, X-rays, ultraviolet waves, infrared waves, microwaves, and radio waves.
All of these different types of energy are "light," even if our human eyes can only "see" part of it. The only difference between them is wavelength (the distance between the peaks of each). Wavelengths get larger as we move across the electromagnetic spectrum from gamma rays to radio waves. The wavelength of visible light is about 1/10th of a micrometer, but the full electromagnetic spectrum includes both shorter and longer wavelengths.
Familiar ways of studying "invisible light" (with wavelengths greater or less than what our eye can see) include x-rays for medical diagnosis and radar for guiding airplanes. By using spectrometers at Mars, scientists can learn a great deal about the planet's composition (what it is made of) and its radiation environment. None of this knowledge would be possible if we only relied on our eyes.
How Spectrometers Work
Spectrometers can essentially spread light out into its wavelengths to create spectra, which look something like rainbow-colored bars. Within these spectra, scientists can study the emission and absorption lines that provide "fingerprints" of any atoms and molecules that may be present. Each atom has a unique fingerprint because they each can only emit or absorb certain energies or wavelengths. That is why the location and spacing of spectral lines--the fingerprint--is unique for each atom. Spectrometers are the instruments that engineers build to detect these kinds of fingerprints.