Rosetta-Alice spectrograph obtains first ultraviolet spectra of cometary surface

NASA's Rosetta-Alice spectrograph has obtained the first far ultraviolet spectra of a cometary surface while orbiting 67P/Churyumov-Gerasimenko.

The ultraviolet imaging spectrometer, which will be the first to study a comet up close, is a shoebox-sized instrument and one-third to one-half the mass of comparable UV instruments, yet with more than 10,000 times as many imaging pixels as the spectrometer aboard Galileo.

As Alice began mapping the comet's surface last month, it made the first far ultraviolet spectra of a cometary surface. From these data, the Alice team discovered that the comet is unusually dark at ultraviolet wavelengths and that the comet's surface - so far - shows no large water-ice patches. Alice is also already detecting both hydrogen and oxygen in the comet's coma, or atmosphere.

Dr. Alan Stern, Alice principal investigator and an associate vice president of the Southwest Research Institute (SwRI) Space Science and Engineering Division said that they were a bit surprised at both just how very unreflective the comet's surface is, and what little evidence of exposed water-ice it shows.

Developed by SwRI, Alice is probing the origin, composition and workings of the comet, gaining sensitive, high-resolution compositional insights that cannot be obtained by either ground-based or Earth-orbital observations. The ultraviolet wavelengths Alice observes contain unique information about the composition of the comet's atmosphere and the properties of its surface.

Researchers said that as the mission progresses, they will continue to search for surface ice patches and ultraviolet color and composition variations across the surface of the comet.