We present the largest sample of flares ever compiled for a single M dwarf, the active M4 star GJ 1243. Over 6100 individual flare events, with energies ranging from 10 29 to 10 33 erg, are found in 11 months of 1-minute cadence data from Kepler. This sample is unique for its completeness and dynamic range. We have developed automated tools for finding flares in short-cadence Kepler light curves, and performed extensive validation and classification of the sample by eye. From this pristine sample of flares we generate a median flare template. This template shows that two exponential cooling phases are present during the white-light flare decay, providing fundamental constraints for models of flare physics. The template is also used as a basis function to decompose complex multipeaked flares, allowing us to study the energy distribution of these events. Only a small number of flare events are not well fit by our template. We find that complex, multi-peaked flares occur in over 80% of flares with a duration of 50 minutes or greater. The underlying distribution of flare durations for events 10 minutes and longer appears to follow a broken power law. Our results support the idea that sympathetic flaring may be responsible for some complex flare events.

Physical processing of Europan surface water ice by thermal relaxation, charged particle bombardment, and possible cryovolcanic activity can alter the percentage of the crystalline form of water ice compared to that of the amorphous form of water ice (the "crystallinity") on Europa's surface. The timescales over which amorphous water ice is thermally transformed to crystalline water ice at Europan surface temperatures (80-130 K) suggests that the water ice there should be primarily in the crystalline form, however, surface bombardment by charged particles induced by Jupiter's magnetic field, and vapor deposition of water ice from Europan plumes, can produce amorphous water ice surface deposits on short timescales.The purpose of this investigation is to determine whether the Europan surface water ice crystallinity derived from ground-based spectroscopic measurements is in agreement with the crystallinity expected based upon temperature and radiation modeling. Using a 1D thermophysical model of Europa's surface, we calculate an integrated full-disk crystallinity of Europa's leading hemisphere by incorporating the thermal relaxation of amorphous to crystalline water ice and the degradation of crystalline to amorphous water ice by irradiation. Concurrently, we derive the full-disk crystallinity of Europa's leading hemisphere using a comparison of near-infrared ground-based spectral observations from Grundy et al. (1999), Busarev et al. (2018), and the Apache Point Observatory in Sunspot, NM, with laboratory spectra from Mastrapa et al. (2008) and the Ice Spectroscopy Lab at the Jet PropulsionLaboratory. We calculate a modeled crystallinity significantly higher than crystallinities derived from ground-based observations and laboratory spectra. This discrepancy may be a result of geophysical processes, such as by vapor-deposited plume material, or it may arise 1 arXiv:2002.04132v1 [astro-ph.EP] 10 Feb 2020 from assumptions and uncertainties in the crystallinity calculations.

Data returned from the Cassini–Huygens mission have strengthened Enceladus, a small icy moon of Saturn, as an important target in the search for life in our solar system. Information gathered from Cassini to support this includes the presence of a subsurface liquid water ocean, vapor plumes and ice grains emanating from its south polar region, and the detection of essential elements and organic material that could potentially support life. However, several outstanding questions remain regarding the connectivity of plume material to the ocean and the composition of the complex organic material. Herein we introduce Tiger, a mission concept developed during the 2020 Planetary Science Summer School at NASA’s Jet Propulsion Laboratory. Tiger is a flyby mission that would help further constrain the habitability of Enceladus through two science objectives: (1) determine whether Enceladus’s volatile inventory undergoes synthesis of complex organic species that are evidence for a habitable ocean, and (2) determine whether Enceladus’s plume material is supplied directly from the ocean or if it interfaces with other reservoirs within the ice shell. To address the science goals in a total of eight flybys, Tiger would carry a four-instrument payload, including a mass spectrometer, a single-band ice-penetrating radar, an ultraviolet imaging spectrograph, and an imaging camera. We discuss Tiger's instrument and mission architecture, as well as the trades and challenges associated with a habitability-focused New Frontiers–class flyby mission to Enceladus.

We analyze 45 spectropolarimetric observations of the eclipsing, interacting binary star V356 Sgr, obtained over a period of ∼21 years, to characterize the geometry of the system's circumstellar material. After removing interstellar polarization from these data, we find the system exhibits a large intrinsic polarization signature arising from electron scattering. In addition, the lack of repeatable eclipses in the polarization phase curves indicates the presence of a substantial pool of scatterers not occulted by either star. We suggest that these scatterers form either a circumbinary disk coplanar with the gainer's accretion disk or an elongated structure perpendicular to the orbital plane of V356 Sgr, possibly formed by bipolar outflows. We also observe small-scale, cycle-tocycle variations in the magnitude of intrinsic polarization at individual phases, which we interpret as evidence of variability in the amount of scattering material present within and around the system. This may indicate a mass transfer or mass loss rate that varies on the time-scale of the system's orbital period. Finally, we compare the basic polarimetric properties of V356 Sgr with those of the well studied β Lyr system; the significant differences observed between the two systems suggests diversity in the basic circumstellar geometry of Roche-lobe overflow systems.

SPICAM-IR, an AOTF spectrometer onboard Mars Express spacecraft with a resolving power of 2,000 covering the spectral range 1-1.7 μm has been observing Mars since 2004. In this wavelength range, it is possible to distinguish between CO2 and H2O ices and measure their band depths. We obtained about 200,000 high-fidelity spectra of CO2 ice in different seasons and locations over the Martian polar caps. The spectra have been associated with slab ice, fine-grained ice, permanent caps, and dark and dirty ice at the cryptic region of the south polar cap. Also, we observed more than 200,000 water ice spectra, specifically its broad feature around 1.5 μm. Water ice is present at the surface or in the atmosphere resulting in a variety of different band depths, often in combination with the CO2 ice. We mapped the equivalent width of 1.43 μm CO2 ice band and the depth of 1.5 μm water ice band, which are the proxies for grain size, and followed their seasonal evolution. From the maps, we produced the edge (outer crocus line) of the CO2 south and north caps for nine Martian Years. The cap edges evolve similarly through all years and are in good agreement with previous OMEGA/Mars Express observations. We also discuss the impact of the global dust storms on the cap edges. Lastly, we interpret some of the water ice observations as water ice clouds in the aphelion cloud belt and the polar hoods.