Alice is a compact, general-purpose UV imaging telescope/spectrometer, which is now flying aboard NASA's New Horizons mission to Pluto and the Kuiper Belt and the ESA/NASA Rosetta asteroid flyby/comet rendezvous mission. The two Alices are called ``P-Alice'' (as part of the Persi suite on New Horizons) and ``R-Alice''.
A ``spectrometer'' is an instrument that separates light into its constituent wavelengths, like a prism, only better. An ``imaging spectrometer'' both separates the different wavelengths of light and produces an image of the target at each wavelength. On the New Horizons mission, Alice will probe the atmospheric composition of Pluto. Alice has two modes of operation: an ``airglow'' mode, which allows measurement of emissions from atmospheric constituents, and an ``occultation'' mode, when either the Sun or a bright star is viewed through the atmosphere producing absorption by the atmospheric constituents. The Alice occultation mode will be used just after New Horizons passes behind Pluto and looks back at the Sun through Pluto's atmosphere.