Hunting for Nonice on Europa's Surface

SPATIALLY RESOLVED SPECTROSCOPY OF EUROPA'S LARGE-SCALE COMPOSITIONAL UNITS AT 3–4 μm WITH KECK NIRSPEC

Authors:

Fischer et al

Abstract:

We present spatially resolved spectroscopic observations of Europa's surface at 3–4 μm obtained with the near-infrared spectrograph and adaptive optics system on the Keck II telescope. These are the highest quality spatially resolved reflectance spectra of Europa's surface at 3–4 μm. The observations spatially resolve Europa's large-scale compositional units at a resolution of several hundred kilometers. The spectra show distinct features and geographic variations associated with known compositional units; in particular, large-scale leading hemisphere chaos shows a characteristic longward shift in peak reflectance near 3.7 μm compared to icy regions. These observations complement previous spectra of large-scale chaos, and can aid efforts to identify the endogenous non-ice species.

The Confusing Spatially Resolved Spectroscopy of Europa

Spatially Resolved Spectroscopy of Europa: The Distinct Spectrum of Large-scale Chaos

Authors:

Fischer et al

Abstract:

We present a comprehensive analysis of spatially resolved moderate spectral resolution near infrared spectra obtained with the adaptive optics system at the Keck Observatory. We identify three compositionally distinct end member regions: the trailing hemisphere bullseye, the leading hemisphere upper latitudes, and a third component associated with leading hemisphere chaos units. We interpret the composition of the three end member regions to be dominated by irradiation products, water ice, and evaporite deposits or salt brines, respectively. The third component is associated with geological features and distinct from the geography of irradiation, suggesting an endogenous identity. Identifying the endogenous composition is of particular interest for revealing the subsurface composition. However, its spectrum is not consistent with linear mixtures of the salt minerals previously considered relevant to Europa. The spectrum of this component is distinguished by distorted hydration features rather than distinct spectral features, indicating hydrated minerals but making unique identification difficult. In particular, it lacks features common to hydrated sulfate minerals, challenging the traditional view of an endogenous salty component dominated by Mg-sulfates. Chloride evaporite deposits are one possible alternative.

Record-breaking Storm Activity on Uranus or did Uranus get Whacked?

Record-breaking storm activity on Uranus in 2014

Authors:

de Pater et al

Abstract:

In spite of an expected decline in convective activity following the 2007 equinox of Uranus, eight sizable storms were detected on the planet with the near-infrared camera NIRC2, coupled to the adaptive optics system, on the 10-m W.M. Keck telescope on UT 5 and 6 August 2014. All storms were on Uranus’ northern hemisphere, including the brightest storm ever seen in this planet at 2.2 μm, reflecting 30% as much light as the rest of the planet at this wavelength. The storm was at a planetocentric latitude of ∼15°N and reached altitudes of ∼330 mbar, well above the regular uppermost cloud layer (methane-ice) in the atmosphere. A cloud feature at a latitude of 32°N, that was deeper in the atmosphere (near ∼2 bar), was later seen by amateur astronomers. We also present images returned from our HST ToO program, that shows both of these cloud features. We further report the first detection of a long-awaited haze over the north polar region.