Science enabled by a far-ultraviolet multi-object spectrograph

Ultraviolet spectroscopy is a critical element of planetary science missions, providing essential information about both planetary surfaces and atmospheres. It is also an excellent complement to infrared spectroscopy and visible imaging because unique molecular absorptions (by atmospheric/plume gases and solid surfaces) and gaseous atomic emissions can be measured exclusively in the UV; in surfaces, unique mineralogical and compositional information is contained in the UV spectral region (e.g. Wagner et al., 1987). While the current generation of UV imaging spectrographs (e.g., Cassini UVIS, New Horizons Alice) have collected a wealth of data from a variety of planetary targets, these narrow-slit instruments will always be fundamentally limited in capability by field of view (FOV) restrictions and the reflection/quantum efficiencies of their optics and detectors. We present an instrument concept, the Ultraviolet Micromirror Imaging Spectrograph (UMIS), and the scientific measurements that it enables. Integral field spectroscopy improves efficiency over traditional long-slit spectroscopy by eliminating the need for scanning across a target. UMIS allows instantaneous access to more spectral information than a narrow-slit spectrograph. Key observations include measuring FUV surface reflectance to constrain grain size/composition in icy satellites, comets, and small bodies, and measuring plumes, coma, or gaseous outbursts in icy satellites and comets through emission or occultation. The targeting capabilities of the micromirrors allow simultaneous tracking of multiple stellar occultations while also observing the FUV surface reflectance. These capabilities would be extremely valuable to future Discovery, New Frontiers, or Flagship missions.