Solar system

Abstract:

The New Horizons encounter with the Pluto system revealed Pluto to have an extremely spatially variable surface with expansive dark, bright, and intermediate terrains, refractory and volatile ices, and ongoing/recent endogenous and exogenous processes. Albedo is useful for understanding volatile transport because it quantifies absorbed solar energy; albedo may also provide insights into surface processes. Four filters of the New Horizons LORRI and MVIC imagers are used to approximate the bolometric (flux-weighted, wavelength-integrated) albedo. The bolometric hemispherical albedo (local energy balance albedo) as a function of the incidence angle of the solar illumination is measured for both Cthulhu and Sputnik Planitia, which are extensive, extreme dark and extreme bright terrains on Pluto. For both terrains, the bolometric hemispherical albedo increases by >30% from 0° to 90° incidence. The incidence-angle-average bolometric hemispherical albedo of Cthulhu is 0.12 ± 0.01, and that of Sputnik Planitia is 0.80 ± 0.06, where uncertainties are estimates based on scatter from different photometric functional approximations. The bolometric Bond albedo (global energy balance albedo) of Cthulhu is 0.12 ± 0.01, and that of Sputnik Planitia is 0.80 ± 0.07. A map of Pluto’s incidence-angle-average bolometric hemispherical albedo is produced. The incidence-angle-average bolometric hemispherical albedo, spatially averaged over areas north of ≈30° S, is ≈0.54. Pluto has three general albedo categories: (1) very low albedo southern equatorial terrains, including Cthulhu; (2) high-albedo terrains, which constitute most of Pluto’s surface; and (3) very high albedo terrains, including Sputnik Planitia. Pluto’s extraordinary albedo variability with location is also spatially sharp at some places

Abstract:

A laboratory study was performed using the Visible Oxford Space Environment Goniometer in which the broadband (350–1250 nm) bidirectional reflectance distribution function (BRDF) of the Winchcombe meteorite was measured, across a range of viewing angles—reflectance: 0°–70°, in steps of 5°; incidence: 15°, 30°, 45°, and 60°; and azimuthal: 0°, 90°, and 180°. The BRDF dataset was fitted using the Hapke BRDF model to (1) provide a method of comparison to other meteorites and asteroids, and (2) to produce Hapke parameter values that can be used to extrapolate the BRDF to all angles. The study deduced the following Hapke parameters for Winchcombe: w = 0.152 ± 0.030, b = 0.633 ± 0.064, and hS = 0.016 ± 0.008, demonstrating that it has a similar w value to Tagish Lake (0.157 ± 0.020) and a similar b value to Orgueil (0.671 ± 0.090). Importantly, the surface profile of the sample was characterized using an Alicona 3D® instrument, allowing two of the free parameters within the Hapke model φ and (Formula presented.), which represent porosity and surface roughness, respectively, to be constrained as φ = 0.649 ± 0.023 and (Formula presented.) = 16.113° (at 500 μm size scale). This work serves as part of the characterization process for Winchcombe and provides a reference photometry dataset for current and future asteroid missions.

Abstract:

<jats:title>Abstract</jats:title> <jats:p>In this work, we present for the first time infrared spectra of Titan from the Spitzer Space Telescope (2004–2009). The data are from both the short wavelength–low resolution (SL; 5.13–14.29 <jats:italic>μ</jats:italic>m, <jats:italic>R</jats:italic> ∼ 60–127) and short wavelength–high resolution (SH; 9.89–19.51 <jats:italic>μ</jats:italic>m, <jats:italic>R</jats:italic> ∼ 600) channels showing the emissions of CH<jats:sub>4</jats:sub>, C<jats:sub>2</jats:sub>H<jats:sub>2</jats:sub>, C<jats:sub>2</jats:sub>H<jats:sub>4</jats:sub>, C<jats:sub>2</jats:sub>H<jats:sub>6</jats:sub>, C<jats:sub>3</jats:sub>H<jats:sub>4</jats:sub>, C<jats:sub>3</jats:sub>H<jats:sub>6</jats:sub>, C<jats:sub>3</jats:sub>H<jats:sub>8</jats:sub>, C<jats:sub>4</jats:sub>H<jats:sub>2</jats:sub>, HCN, HC<jats:sub>3</jats:sub>N, and CO<jats:sub>2</jats:sub>. We compare the results obtained for Titan from Spitzer to those of the Cassini Composite Infrared Spectrometer (CIRS) for the same time period, focusing on the 16.35–19.35 <jats:italic>μ</jats:italic>m wavelength range observed by the SH channel but impacted by higher noise levels in the CIRS observations. We use the SH data to provide estimated haze extinction cross sections for the 16.67–17.54 <jats:italic>μ</jats:italic>m range that are missing in previous studies. We conclude by identifying spectral features in the 16.35–19.35 <jats:italic>μ</jats:italic>m wavelength range that could be analyzed further through upcoming James Webb Space Telescope Cycle 1 observations with the Mid-Infrared Instrument (5.0–28.3 <jats:italic>μ</jats:italic>m, <jats:italic>R</jats:italic> ∼ 1500–3500). We also highlight gaps in the current spectroscopic knowledge of molecular bands, including candidate trace species such as C<jats:sub>60</jats:sub> and detected trace species such as C<jats:sub>3</jats:sub>H<jats:sub>6</jats:sub>, that could be addressed by theoretical and laboratory study.</jats:p>