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

Comprehensive Photometry of the Rings and 16 Satellites of Uranus with the Hubble Space Telescope

https://digital.csic.es/bitstream/10261/8184/3/Post_print_Nna%20Mvondo%20et%20al_2008%282%29.pdf

Experimental impact shock chemistry on planetary icy satellites

The discovery of the four large satellites of Jupiter by Galileo Galilei in January 1610 was one of the most significant events in the history of science. Galileo’s observations of moons appearing to move from one side of the planet to the other provided support for the Copernican view of the Universe by showing that celestial objects did not all orbit the Earth. His claim as the first observer of what he called the ‘Medicean planets’ was hotly disputed by the German astronomer Simon Marius. Marius claimed to have observed the satellites in November 1609 and there is little doubt that he was using a telescope to study the heavens around the same time as Galileo. However, Galileo published his observations while there is no record of those of Marius. In Galileo’s honour, the four large satellites of Jupiter are often now referred to as the Galilean satellites.

The satellites of the outer planets

Visible and Near-Infrared Photometry of the Centaur Objects 1995 GO and 5145 Pholus

We present a new spectrum of 5145 Pholus between 1.15 and 2.4 microns. We model this, and the previously published (0.4-1.0 microns) spectrum, using Hapke scattering theory. The 2.04 micron band of H2O ice is seen in absorption, as well as a strong band at 2.27 Am, interpreted as frozen methanol and/or the methanol photo product hexamethylenetetramine (HMT). The presence of small molecules is indicative of a chemically primitive surface, since heating removes the light hydrocarbons in favor of macromolecular carbon typically found in carbonaceous meteorites. The unusually red slope of Pholus' spectrum is matched by fine grains of Titan tholin, as found previously. Object 1993 HA2, which has an orbit similar to that of 5145 Pholus, is similarly red, but there are as yet no observations of absorption bands in its spectrum. We present a model for the composite spectrum of all spectroscopic and photometric data available for 5145 Pholus and conclude that this is a primitive object which has yet to be substantially processed by solar heat.

The Composition of Planetesimal 5145 Pholus

Here we report the combination of new near-ir spectra (1.45-2.48 micrometers), of Titania and Oberon obtained in September 1995 at a resolving power of approx. 800, with older near-ir observations (0.5- 1.44 micrometers), and recent UV (0.22-0.48 micrometers) observations obtained with HST. Previous interpretations suggest these surfaces are chiefly composed of water ice and varying amounts of spectrally neutral material. The new near-ir data provide the opportunity to search for absorption bands that could be attributable to surface materials other than water ice and because the combined spectra include such a broad wavelength region, to undertake improved models of water and neutral components on the surface. The calculated near-ir geometric albedos clearly exhibit three broad spectral features. Two (1.52- & 2.05 micrometer) have previously been used to demonstrate the presence of water ice on these satellites. The third (approx. 1.65 micrometer), suggests the presence of hexagonal water ice at low temperatures, and may provide a mechanism of estimating the surface temperature. There is no spectral evidence for ices of CO2, CO, NH3 or CH4. At UV wavelengths there is a broad absorption near 0.27-0.28 micrometer previously attributed to OH formed by magnetospheric-surface interactions and retained at the low surface temperatures of these satellites. Surface components used in a Hapke scattering models include values for a combination of irradiated water ice in the UV and hexagonal water ice at 100k in the near-ir (IR), amorphous carbon (AC), and tholins (T) (produced from gas and solid). Results of these models suggest the surfaces of Titania/Oberon are composed of IW (-77/52%) with AC the next most abundant component (approx. 19/52%) and finally T (approx. 4/7%).

Titania and Oberon: Surface Composition from New Near-Infrared Observations and Reflectance Models

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The Composition of Planetesimal 5145 Pholus

Titania and Oberon: Surface Composition from New Near-Infrared Observations and Reflectance Models