Juno is the first polar orbiter around Jupiter. Juno possesses a suite of instruments designed to measure the electron and ion populations in the Jupiter magnetosphere, leading to the powerful Jovian aurorae. The Ultraviolet Spectrograph onboard Juno (Juno-UVS) is a photon-counting imaging spectrograph (68-210 nm), designed to observe and characterize Jupiter's far-ultraviolet aurorae. The instrument borrows heavily from previous Alice and UVS instruments led by Southwest Research Institute (New Horizons and Rosetta Alices, LRO-LAMP), with several major improvements. The pointing flexibility offered by the UVS scan mirror combined with Juno's spin allows UVS access to half of the sky at any given moment. This paper describes how we leverage this extensive database to track the evolution of Juno-UVS calibration with time throughout the mission. UVS observes 7.2°×360°-long swaths of the sky for each rotation of the spacecraft (nominally 2 rpm). This paper describes how the very substantial amount of stellar spectra has been used to monitor the health of the instrument over the mission. As of PJ14 (2018 July 16), more than 8700 spectra of O, A, and B stars have been extracted in the V-magnitude range of ∼0-7, and more than 99% of the sky was mapped. Selected stars among this list were used to calibrate the UVS bandpass, using observations from the International Ultraviolet Explorer and the Hubble Space Telescope. The retrieved effective area of the instrument is 0.30±0.03 cm 2 at 125 nm, 0.15±0.02 cm 2 at 140 nm, and 0.05±0.01 cm 2 at 160 nm.

The lunar South Pole crater Amundsen is a prime location to study the effects of space weathering in the far ultraviolet. Amundsen's equator‐facing terrace walls are highly illuminated while the northern side of the crater has permanently shaded regions (PSRs). Using data from the Lunar Reconnaissance Orbiter Lyman Alpha Mapping Project, we investigate signatures of space weathering in different regions of Amundsen. We find that regions of the surface that receive large amounts of solar illumination and solar wind flux (e.g., the southern terrace walls) display high Lyman‐α albedos and blue spectral slopes in the 175–190‐nm region, indicative of increased regolith maturity due to solar wind weathering and thermal cycling. Amundsen's PSRs, however, receive no direct solar illumination and very little solar wind flux and have a lower albedo across Lyman Alpha Mapping Project's entire band pass (57–197 nm) than illuminated regions of the crater. We conclude that the low PSR albedos correspond to high regolith porosity in the PSRs. These PSRs are extremely cold regions with very minor thermal cycling. Thermal cycling might be a process that reduces porosity in regions of the crater exposed to a wide range of temperatures, thus increasing their albedos across the entire wavelength range. However, our analysis of the present data set was unable to uniquely identify its role. The low albedos in the PSRs may also result from extreme charging effects inside the PSRs, causing lofting and redeposition of dust, as well as dielectric breakdown, which would act to increase regolith porosity.

The lunar poles contain regions that experience extreme temperature conditions, enabling them to freeze and trap water (Paige, Siegler, et al., 2010;Watson et al., 1961b). Modeling evidence of water delivery to the lunar surface by various mechanisms, such as comet or meteoroid bombardment, solar wind implantation, and outgassing/eruptions have been postulated (e.g.,