Planetary ultraviolet spectroscopy

The emission spectra of a planetary dayglow are produced by the resonance scattering of atoms, the fluorescence scattering of molecules, and the photoelectron excitation of the atoms and molecules that are the major constituents of the atmosphere. The absorption spectra of a planetary atmosphere are the result of the combination of ground reflection, atmospheric scattering, and atmospheric absorption. The observation of these spectra from a planetary spacecraft is accomplished by observing the bright limb, disk, terminator, and dark limb of the planet with a telescope and scanning uv spectrometer. Ultraviolet spectroscopy can determine if the atoms and molecules basic to life are present in a planetary atmosphere: in particular, molecular nitrogen and the photodissociation products of water vapor. Ultraviolet spectrometer experiments can also tell if the atmosphere has been changed by the presence of life such as the production of oxygen from photosynthesis. Local regions of photosynthetic oxygen production will produce ozone which is detectable by uv spectroscopy.