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Polyphase Mid-Latitude Glaciation on Mars: Chronology of the Formation of Superposed Glacier-Like Forms from Crater-Count Dating
Hepburn, A. J.; Hubbard, B.; Ng, F. S. L. +2 more
Reconstructing Mars's glacial history informs understanding of its physical environment and past climate. The known distribution of viscous flow features (VFFs) containing water ice suggests that its mid-latitudes were glaciated during the Late Amazonian period (the last several hundred million years). The identification of a subgroup of VFFs—call…
Ganymede's Far-Ultraviolet Reflectance: Constraining Impurities in the Surface Ice
Nichols, J. D.; Raut, U.; Retherford, K. D. +2 more
We present reflectance spectra of Ganymede's leading and trailing hemispheres in the wavelength range 138-215 nm, obtained by the Hubble Space Telescope Cosmic Origins Spectrograph (HST/COS) in 2014. The most notable feature of both spectra is the absence of a sharp water absorption edge at ~165 nm, seen in laboratory measurements of ice reflectiv…
Paleolakes in the Northwest Hellas Region, Mars: Implications for the Regional Geologic History and Paleoclimate
Xiao, Long; Glotch, Timothy D.; Zhao, Jiannan
Hellas basin is one of the largest and oldest impact basins on the Martian surface. Its surrounding highland regions have undergone complicated geologic processes after the formation of Hellas basin. However, the geologic and climatic histories of the highlands surrounding Hellas are still unclear. Paleolakes provide us clues to answer these quest…
Small Impact Crater Populations on Saturn's Moon Tethys and Implications for Source Impactors in the System
Ferguson, S. N.; Rhoden, A. R.; Kirchoff, M. R.
Current estimates place the ages of the inner Saturnian satellites (Mimas, Enceladus, Tethys, Dione, and Rhea) between 4.5 Gyr and 100 Myr. These estimates are based on impact crater measurements and dynamical simulations, both of which have uncertainties. Models of satellite evolution are inherently simplified and rely on uncertain or unknown par…
A Survey of Small-Scale Waves and Wave-Like Phenomena in Jupiter's Atmosphere Detected by JunoCam
Wong, Michael H.; Fletcher, Leigh N.; Ingersoll, Andrew P. +17 more
In the first 20 orbits of the Juno spacecraft around Jupiter, we have identified a variety of wave-like features in images made by its public-outreach camera, JunoCam. Because of Juno's unprecedented and repeated proximity to Jupiter's cloud tops during its close approaches, JunoCam has detected more wave structures than any previous surveys. Most…
Studies of the 2018/Mars Year 34 Planet-Encircling Dust Storm
Guzewich, S. D.; Fedorova, A. A.; Kahre, M. A. +1 more
Mars' planet-encircling or global dust storms (GDSs) are an iconic and enigmatic feature of the Red Planet. Occurring every few Mars Years (MYs), on average, they are a stochastic process in the otherwise largely repeatable annual cycle of martian weather. In 2018 (MY 34 in the calendar of Clancy et al. [2000],
Possible Transient Luminous Events Observed in Jupiter's Upper Atmosphere
Wong, Michael H.; Gérard, Jean-Claude; Kammer, Joshua A. +10 more
Eleven transient bright flashes were detected in Jupiter's atmosphere using the ultraviolet spectrograph instrument on the Juno spacecraft. These bright flashes are only observed in a single spin of the spacecraft and their brightness decays exponentially with time, with a duration of ∼1.4 ms. The spectra are dominated by H2 Lyman band …
Late Amazonian Ice Survival in Kasei Valles, Mars
Hepburn, A. J.; Hubbard, B.; Ng, F. S. L. +1 more
High-obliquity excursions on Mars are hypothesized to have redistributed water from the poles to nourish mid-latitude glaciers. Evidence of this process is provided by different types of viscous flow features (ice-rich deposits buried beneath sediment mantle) located there today, including lobate debris aprons (LDAs). During high-obliquity extreme…
Updated Equipotential Shapes of Jupiter and Saturn Using Juno and Cassini Grand Finale Gravity Science Measurements
Helled, Ravit; Folkner, William M.; Parisi, Marzia +2 more
A commonly used shape model for the giant plants of Jupiter and Saturn is an oblate ellipsoid, a simplified model of the equipotential shape. The ellipsoidal shape models were originally derived from radio occultation data and gravity data after the Voyager flybys in 1979. Through precise Doppler tracking of NASA's Juno and Cassini spacecraft tele…
Compositional Measurements of Saturn's Upper Atmosphere and Rings from Cassini INMS
Yelle, R. V.; Hörst, S. M.; Koskinen, T. T. +4 more
The Cassini spacecraft's last orbits directly sampled Saturn's thermosphere and revealed a much more chemically complex environment than previously believed. Observations from the Ion and Neutral Mass Spectrometer (INMS) aboard Cassini provided compositional measurements of this region and found an influx of material raining into Saturn's upper at…