A thermophysical model is presented that considers surface roughness, cast shadows, multiple or single scattering of radiation, visual and thermal infrared self heating, as well as heat conduction in one or three dimensions. The code is suitable for calculating infrared spectral energy distributions for spatially resolved or unresolved minor Solar System bodies without significant atmospheres or sublimation, such as the Moon, Mercury, asteroids, irregular satellites or inactive regions on comet nuclei. It is here used to explore the effects of surface roughness on spatial scales small enough for heat conduction to erase lateral temperature gradients. Analytically derived corrections to one-dimensional models that reproduce the results of three-dimensional modeling are presented. We find that the temperature of terrains with such small-scale roughness is identical to that of smooth surfaces for certain types of topographies and non-scattering material. However, systematic differences between smooth and rough terrains are found for scattering materials, or topographies with prominent positive relief. Contrary to common beliefs, the roughness on small spatial scales may therefore affect the thermal emission of Solar System bodies. (C) 2014 Elsevier Inc. All rights reserved.

Synchrotron X-ray powder diffraction has been used to explore the water-rich (<50 wt.% H2SO4) region of the sulfuric acid and water binary phase diagram at temperatures between 80 and 285 K. The phase relations that are determined demonstrate that, on laboratory timescales, sulfuric acid hydrates crystallize as mixtures of phases. Flur forms of sulfuric acid hydrates were observed along with ice lh, with their proportions dependent on temperature and sample H2SO4 wt.%. The charting of these phase relations has revealed a transformation between hydrate forms, which could be utilized as a marker for areas of higher heat flow on the surfaces of the Galilean ice moons. Crown Copyright (C) 2014 Published by Elsevier Inc. All rights reserved.

The exosphere of an atmosphereless icy moon is the result of different surface release processes and subsequent modification of the released particles. At Europa icy moon, water molecules are directly released, but photolysis and radiolysis due to solar UV and Jupiter's magnetospheric plasma, respectively, can result in OH, H, O and (possibly) H-2 production. These molecules can recombine to reform water and/or new chemical species. As a consequence, Europa's neutral environment becomes a mixture of different molecules, among which, H2O dominates in the highest altitudes and O-2, formed mainly by radiolysis of ice and subsequent release of the produced molecules, prevails at lower altitudes. In this work, starting from a previously developed Monte Carlo model for the generation of Europa's exosphere, where the only considered species was water, we make a first attempt to simulate also the H-2 and O-2 components of the neutral environment around Europa, already observed by the Hubble Space Telescope and the Ultraviolet Imaging Spectrograph on board Cassini, during its flyby of Jupiter. Considering a specific configuration where the leading hemisphere coincides with the sunlit hemisphere, we estimate along the Europa-Sun line an O-2 column density of about 1.5 x 10(19) m(-2) at the dayside and 3 x 10(18) m(-2) at the nightside. In this work we also improve our previous estimation of the sputtered H2O exosphere of this moon, taking into consideration the trailing-leading asymmetry in the magnetospheric ion bombardment and the energy and temperature dependences of the process yields. We find that a density of 1.5 x 10(12) H2O/m(3) is expected at altitudes similar to 0.1R(E) above the surface of the trailing hemisphere. Additionally, we calculate the escape of H2O, O-2 and H-2. The total number of neutral atoms in Europa's neutral torus, is estimated to be in the range 7.8 x 10(32)-3.3 x 10(33). (C) 2012 Elsevier Inc. All rights reserved.