Retrieving Neptune's aerosol properties from Keck OSIRIS observations. I. Dark regions

We present and analyze three-dimensional data cubes of Neptune from the OSIRIS integral-field spectrograph on the 10-m Keck telescope, from July 2009. These data have a spatial resolution of 0.035"/pixel and spectral resolution of R~3800 in the H and K broad bands. We focus our analysis on regions of Neptune's atmosphere that are near-infrared dark- that is, free of discrete bright cloud features. We use a forward model coupled to a Markov chain Monte Carlo algorithm to retrieve properties of Neptune's aerosol structure and methane profile above ~4 bar in these near-infrared dark regions. Using a set of high signal-to-noise spectra in a cloud-free band from 2-12N, we find that Neptune's cloud opacity is dominated by a compact, optically thick cloud layer with a base near 3 bar and composed of low albedo, forward scattering particles, with an assumed characteristic size of ~1$\mu$m. Above this cloud, we require a vertically extended haze of smaller (~0.1 $\mu$m) particles, which reaches from the upper troposphere (~0.6 bar) into the stratosphere. The particles in this haze are brighter and more isotropically scattering than those in the deep cloud. When we extend our analysis to 18 cloud-free locations from 20N to 87S, we observe that the optical depth in aerosols above 0.5 bar decreases by a factor of 2-3 or more at mid- and high-southern latitudes relative to low latitudes. We also consider Neptune's methane (CH$_4$) profile, and find that our retrievals indicate a strong preference for a low methane relative humidity at pressures where methane is expected to condense. Our preferred solution at most locations is for a methane relative humidity below 10% near the tropopause in addition to methane depletion down to 2.0-2.5 bar. We tentatively identify a trend of lower CH$_4$ columns above 2.5 bar at mid- and high-southern latitudes over low latitudes.Comment: Published in Icarus: 15 September 201

Occultation Light Curves of Io's Hot Spots in 2014

We present ground-based observations of Io during Spring 2014, contributing to decadal timelines of individual hot spots' volcanic activity

Observational constraints on the distribution and temperature dependence of H_2O_2 on the surface of Europa

We use Keck NIRSPEC to investigate the geographic distribution of hydrogen peroxide, a potentially biologically important oxidant, on the surface of Europa. Contrary to expectation, we see the highest abundances at low latitudes, potentially correlated with geologically young chaos terrain. We also use NASA IRTF SpeX spectra of Europa before and after eclipse to investigate the extent to which temperature controls equilibrium hydrogen peroxide concentrations on the surface. During eclipse, Europa's surface temperature falls 10-20 K. If temperature were a significant control on peroxide concentrations, then the hydrogen peroxide band strengths should be different pre- and post-eclipse. Ultimately, these investigations will help further our understanding of the surface, and perhaps subsurface, composition of Europa

Thermal Properties of the Icy Galilean Satellites from Millimeter ALMA Observations

We present spatially-resolved maps of the leading and trailing hemispheres of Europa, Ganymede, and Callisto from ALMA millimeter wavelength observations

Occultation Light Curves of Io's Hot Spots in 2014

We present ground-based observations of Io during Spring 2014, contributing to decadal timelines of individual hot spots' volcanic activity

Observational constraints on the distribution and temperature dependence of H_2O_2 on the surface of Europa

We use Keck NIRSPEC to investigate the geographic distribution of hydrogen peroxide, a potentially biologically important oxidant, on the surface of Europa. Contrary to expectation, we see the highest abundances at low latitudes, potentially correlated with geologically young chaos terrain. We also use NASA IRTF SpeX spectra of Europa before and after eclipse to investigate the extent to which temperature controls equilibrium hydrogen peroxide concentrations on the surface. During eclipse, Europa's surface temperature falls 10-20 K. If temperature were a significant control on peroxide concentrations, then the hydrogen peroxide band strengths should be different pre- and post-eclipse. Ultimately, these investigations will help further our understanding of the surface, and perhaps subsurface, composition of Europa

Observational Constraints on the Distribution and Temperature Dependence of H_2O_2 on the Surface of Europa

We present observations of H_2O_2 on the surface of Europa. We map H_2O_2 across the surface and investigate its geographic variability. We also examine temperature effects on its abundance by observing the 3.5 µm band before and after eclipse

Diagnosis and Threat Detection Capabilities of the SERENITY Monitoring Framework

The SERENITY monitoring framework offers mechanisms for diagnosing the causes of violations of security and dependability (S&D) properties and detecting potential violations of such properties, called “threats”. Diagnostic information and threat detection are often necessary for deciding what an appropriate reaction to a violation is and taking pre-emptive actions against predicted violations, respectively. In this chapter, we describe the mechanisms of the SERENITY monitoring framework which generate diagnostic information for violations of S&D properties and detecting threats

Thermal Properties of the Icy Galilean Satellites from Millimeter ALMA Observations

We present spatially-resolved maps of the leading and trailing hemispheres of Europa, Ganymede, and Callisto from ALMA millimeter wavelength observations