We have investigated the H 2 SO 4 /H 2 O binary liquid/solid phase diagram using a highly sensitive differential scanning calorimeter (DSC) and infrared spectroscopy of thin films. In particular we have sought to investigate the region from pure ice to sulfuric acid tetrahydrate (SAT), including a detailed look at the sulfuric acid octahydrate (SAO). Our studies have found that there is a unique, repeatable IR spectrum for SAO. Our spectrum is not merely a combination of spectra of ice and sulfuric acid tetrahydrate (SAT), as has been previously suggested could be the case by Zhang et al. (Zhang, R.; Wooldridge, P. J.; Abbatt, J. P. D.; Molina, M. J. J. Phys. Chem. 1993, 97, 7351). From our thermal analysis experiments, we have identified the melting transition of SAO. We report for the first time in the literature the enthalpy of fusion of SAO. We have also determined from our studies using the energies of fusion of ice and the various hydrates of H 2 SO 4 that SAO is a major component of H 2 SO 4 solutions in the range 20-40 wt % when they freeze. Our results indicate that SAO could be present in solid or partially frozen polar stratospheric and upper tropospheric cloud particles. Finally, we make a comment based on our results regarding the stoichiometric composition of SAO.

Data from the Lunar Reconnaissance Orbiter Lyman Alpha Mapping Project and Diviner are consistent with surface water on the Moon varying in abundance with both terrain type and local time/temperature. A thermal desorption model including latitudinally varying desorption activation energy reproduces the observations. We interpret the observed variability in spectral slopes as water molecules in the uppermost lunar regolith (<1% of a monolayer) thermally adsorbing and desorbing from grains depending upon the local temperature and availability of chemisorption sites. The Lyman Alpha Mapping Project data also demonstrate that in the Earth's magnetotail, where the solar wind source of protons is absent, a decrease in H2O on the surface is not observed. This rules out a steady state process involving a prompt solar wind source and favors a migration mechanism for the distribution of adsorbed water on the Moon.

F‐ and M‐color center formation (decay) was observed during (after) irradiation of sodium chloride crystal grains with 10 keV electrons as a function of temperature, radiation dose rate, and radiation dose. The F centers (peak center: 460 nm) were found to form and decay at a faster rate than the M centers (peak center: 720 nm). These effects were influenced by temperature and possibly by irradiation dose rate. Tracking the band depth ratio of the color center features during irradiation could enable age determination of geologically very young features on the surface of Europa and other icy ocean worlds.

The earliest dynamic and thermal history of the Moon is not well understood. The hydrogen content of deposits near the lunar poles may yield insight into this history, because these deposits (which are probably composed of water ice) survive only if they remain in permanent shadow. If the orientation of the Moon has changed, then the locations of the shadowed regions will also have changed. The polar hydrogen deposits have been mapped by orbiting neutron spectrometers, and their observed spatial distribution does not match the expected distribution of water ice inferred from present-day lunar temperatures. This finding is in contrast to the distribution of volatiles observed in similar thermal environments at Mercury's poles. Here we show that polar hydrogen preserves evidence that the spin axis of the Moon has shifted: the hydrogen deposits are antipodal and displaced equally from each pole along opposite longitudes. From the direction and magnitude of the inferred reorientation, and from analysis of the moments of inertia of the Moon, we hypothesize that this change in the spin axis, known as true polar wander, was caused by a low-density thermal anomaly beneath the Procellarum region. Radiogenic heating within this region resulted in the bulk of lunar mare volcanism and altered the density structure of the Moon, changing its moments of inertia. This resulted in true polar wander consistent with the observed remnant polar hydrogen. This thermal anomaly still exists and, in part, controls the current orientation of the Moon. The Procellarum region was most geologically active early in lunar history, which implies that polar wander initiated billions of years ago and that a large portion of the measured polar hydrogen is ancient, recording early delivery of water to the inner Solar System. Our hypothesis provides an explanation for the antipodal distribution of lunar polar hydrogen, and connects polar volatiles to the geologic and geophysical evolution of the Moon and the bombardment history of the early Solar System.

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