Energetic Ion and Electron Irradiation of the Icy Galilean Satellites

Observations of Saturn9s satellite Enceladus using Cassini9s Visual and Infrared Mapping Spectrometer instrument were obtained during three flybys of Enceladus in 2005. Enceladus9 surface is composed mostly of nearly pure water ice except near its south pole, where there are light organics, CO 2 , and amorphous and crystalline water ice, particularly in the region dubbed the “tiger stripes.” An upper limit of 5 precipitable nanometers is derived for CO in the atmospheric column above Enceladus, and 2% for NH 3 in global surface deposits. Upper limits of 140 kelvin (for a filled pixel) are derived for the temperatures in the tiger stripes.

/pdf/composition-and-physical-properties-of-enceladus-surface-27puyr3fk7.pdf

Composition and physical properties of Enceladus' surface

Context. The Kuiper belt is formed of planetesimals which failed to grow to planets and its dynamical structure has been affected by Neptune. The classical Kuiper belt contains objects both from a low-inclination, presumably primordial, distribution and from a high-inclination dynamically excited population. Aims. Based on a sample of classical trans-Neptunian objects (TNOs) with observations at thermal wavelengths we determine radiometric sizes, geometric albedos and thermal beaming factors for each object as well as study sample properties of dynamically hot and cold classicals. Methods. Observations near the thermal peak of TNOs using infrared space telescopes are combined with optical magnitudes using the radiometric technique with near-Earth asteroid thermal model (NEATM). We have determined three-band flux densities from Herschel/PACS observations at 70.0, 100.0 and 160.0 mu m and Spitzer/MIPS at 23.68 and 71.42 mu m when available. We use reexamined absolute visual magnitudes from the literature and ground based programs in support of Herschel observations. Results. We have analysed 18 classical TNOs with previously unpublished data and re-analysed previously published targets with updated data reduction to determine their sizes and geometric albedos as well as beaming factors when data quality allows. We have combined these samples with classical TNOs with radiometric results in the literature for the analysis of sample properties of a total of 44 objects. We find a median geometric albedo for cold classical TNOs of 0.14(-0.07)(+0.09) and for dynamically hot classical TNOs, excluding the Haumea family and dwarf planets, 0.085(-0.045)(+0.084). We have determined the bulk densities of Borasisi-Pabu (2.1(-1.2)(+2.6) g cm(-3)), Varda-Ilmare (1.25(-0.43)(+0.40), g cm(-3)) and 2001 QC(298) (1.14(-0.30)(+0.34) g cm(-3)) as well as updated previous density estimates of four targets. We have determined the slope parameter of the debiased cumulative size distribution of dynamically hot classical TNOs as q = 2.3 +/- 0.1 in the diameter range 100 \textless D \textless 500 km. For dynamically cold classical TNOs we determine q = 5.1 +/- 1.1 in the diameter range 160 \textless D \textless 280 km as the cold classical TNOs have a smaller maximum size.

/pdf/tnos-are-cool-a-survey-of-the-trans-neptunian-region-x-3me5vzjb8o.pdf

“TNOs are Cool”: A survey of the trans-Neptunian region - X. Analysis of classical Kuiper belt objects from Herschel and Spitzer observations

[1] The water ice on the three outermost Galilean satellites of Jupiter has a lattice structure that can vary from crystalline to amorphous. Amorphous ice is crystallized by heating, while crystalline ice is amorphized through disruption by particle radiation. We determine ice lattice order using infrared spectra from the Near Infrared Mapping Spectrometer on the Galileo Jupiter orbiter. The shape of the reflectance peak near 3.1 μm is diagnostic of the lattice order in the top micrometers of the surface. A narrow, temperature-sensitive band near 1.65 μm, from ∼1 mm depth, is missing for amorphous ice. Spectral averages of >100 pixels were used for Europa and Callisto, because of high radiation noise and small ice amounts, respectively. Model comparisons show that the surface ice is predominantly amorphous on Europa and predominantly crystalline on Callisto, while both types of ice are found on Ganymede. The distribution of Ganymede ice properties shows a broad global pattern of more amorphous ice in the high-latitude Jovian-facing hemisphere and in the low-latitude trailing hemisphere. The ice at ∼1 mm depth on all three satellites is predominantly crystalline. The radiation flux increases by ∼300 times between Callisto and Europa, while the thermal crystallization rate may vary over five orders of magnitude among the three satellites (being the fastest at Callisto). The occurrence of crystalline and amorphous ice suggests a balance between the disruption and crystallization, with Callisto dominated by thermal crystallization and Europa by radiative disruption, and with nearly equal rates between the two processes at Ganymede.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2003JE002149

Amorphous and crystalline ice on the Galilean satellites: A balance between thermal and radiolytic processes

/pdf/mid-and-far-infrared-spectroscopic-studies-of-the-influence-y42q9ca0ly.pdf

Mid- and far-infrared spectroscopic studies of the influence of temperature, ultraviolet photolysis and ion irradiation on cosmic-type ices

Near-Infrared Spectra of Icy Outer Solar System Surfaces: Remote Determination of H2O Ice Temperatures

We present new albedo spectra of Triton and Pluto-Charon, covering the 2.8–4.1 μm wavelength range at a spectral resolution of ~60. The new data reveal three strong CH4 ice absorption bands, as well as additional absorption around 2.9 and 4.1 μm in the spectra of both bodies, which we tentatively attribute to widely distributed H2O ice, along with CO2 and/or SO2 ices. Since these species are nonvolatile at typical Triton and Pluto surface temperatures, widespread distribution of any of them in volatile-rich regions challenges current understanding of the surfaces of Pluto and Triton, in which more volatile, mobile ices are thought to be segregated from less volatile species. Our data suggest that small, nonvolatile ice particles on Triton and Pluto may be undergoing redistribution by aeolian transport in seasonal sublimation winds.

/pdf/spectroscopy-of-pluto-and-triton-at-3-4-microns-possible-1voiu4lsuc.pdf

Spectroscopy of Pluto and Triton at 3-4 Microns: Possible Evidence for Wide Distribution of Nonvolatile Solids

From July 2001 to June 2002, an HST snapshot program obtained V, R and I photometry for 72 TNOs. The TNOs were sorted by dynamical class, and Spearman rank correlation statistics were calculated for each combination of color and orbital parameter. No strong correlations were found for the combined sample of TNOs, the resonant TNOs, or the non-resonant TNOs (classical). The results presented here suggest that if correlations reported by other authors are real, they are evident only at shorter wavelengths than observed in our survey.

HST Photometry of trans-Neptunian Objects

Volatile Transport Implications from the New Horizons Flyby of Pluto

Correlating Pluto's Albedo Distribution to Long Term Insolation Patterns

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