0 Assigned ID: 5815 ----- Attempting Submission 1 (Tue Mar 26 23:16:05 GMT 2024) ----- HST Phase I Proposal 5815 successfully submitted. Receipt: # 5815-1 ----- Attempting Submission 2 (Tue Mar 26 23:25:53 GMT 2024) ----- ORBITAL VISIBILITY OVERRUN Resubmitting with updated target acquisition on Pluto and slightly reduced science exposures to account for the slew to Charon. The wavecal is deferred to after occultation. -1773977876 ----- Attempting Submission 1 (Mon Aug 12 21:27:55 GMT 2024) ----- ----- Attempting Submission 2 (Sun Mar 09 21:16:58 GMT 2025) ----- The orbital visibility overrun seems to just be referring to our added wavecal exposure, which should be ok to perform in Earth occultation. The New Horizons mission revealed that Charon could be an example of an "extinct ocean world", whose once liquid layer has completely frozen. The extensive tectonism and smooth plains on Charon are consistent with the pressure-driven resurfacing of a freezing subsurface ocean, and suggest that once-oceanic materials could have reached the surface. Intriguingly, Charon's infrared spectrum shows evidence for widespread ammoniated material suggested to be possible ammonia hydrates or, most recently, ammonium salts like NH4Cl, both of which could have become concentrated as the subsurface liquid froze. While this interpretation from just the infrared data is ambiguous, visible-wavelength spectra sensitive to absorptions from irradiation-induced crystal defects known as "color centers" provide a diagnostic means of salt detection that has been successfully implemented for Europa, Ceres, and Mars. Both the proposed NH4Cl on Charon and the NaCl detected on these other bodies should form during the freezing of NH4-, Cl-, and Na-bearing brines and, thus, are plausible surface materials for Charon. Both salts exhibit strong color-center absorptions across the 300 - 550 nm wavelengths that have remained totally unexplored for Charon in the nearly 50 years since its discovery. We propose a simple, single-orbit program with HST/STIS that will provide the first-ever spectral coverage of Charon across these wavelengths and enable a robust search for these salt color-center absorptions. This single-orbit request has the potential to transform our understanding of the connection between Charon's long-changed internal structure and its modern-day surface. The observations entail a single orbit of HST, druring which we will acquire and observe Charon with STIS using the 52"x0.2" slit and G430L first-order spectroscopy mode. Our observations are straightforward and consist of a single visit and pointing, including one science exposure with the maximum exposure time allowable by the orbit constraints. To maximize this exposure time, we defer the wavelength calibration until after Earth occultation. Our team has extensive experience with HST/STIS reflectance spectroscopy of Solar System targets. Our team used HST/STIS observations to discover NaCl color centeres on Europa, and has also used HST/STIS to observe the other Galilean satellites and several small bodies throughout the Solar System. PI Samantha Trumbo is a planetary astronomer who is an expert on the surface compositions of icy bodies. She has extensive experience with ground- and space-based observations from the UV through near-infrared and is the PI of 2 Cycle 30 HST programs using HST/STIS. She will oversee all aspects of the project. Co-I Michael Brown is a planetary astronomer who is an expert in Solar System observations of planetary satellites and small bodies, including other TNOs. In addition, he runs the Planetary Ice Chemistry Lab at Caltech and has expertise in laboratory experiments on radiation chemistry. He will aid in spectral interpretation. Solar System Astronomy 6 false false false false false false SUPPORTED SOLAR SYSTEM NO SATELLITE Charon STD=PLUTO STD=CHARON EARTH SOLAR SYSTEM NO DWARF-PLANET Pluto STD=PLUTO EARTH STIS/CCD Spectroscopic No No G430L 4300 1741554657233 /private/var/folders/5l/q1nxxvqd13d2150cg8wy0lbc0000gq/T/OPVisit5283112065289309073.xml Using ephemeris for target 17773-01-PLUTO ephemeris data for target 17773-01-PLUTO does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 24.214 to 26.120. ephemeris interval: 25.059 to 27.060 Using ephemeris for target 17773-01-CHARON ephemeris data for target 17773-01-CHARON does not cover planning interval. Physical constraints are assumed to be unschedulable outside of the ephemeris data. Planning interval: 24.214 to 26.120. ephemeris interval: 25.059 to 27.060 The scheduling data was generated by CASM 33.0. CASM was run in Phase II mode. 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