2,391 research outputs found
On the chemical composition of Titan's dry lakebed evaporites
Titan, the main satellite of Saturn, has an active cycle of methane in its
troposphere. Among other evidence for a mechanism of evaporation at work on the
ground, dry lakebeds have been discovered. Recent Cassini infrared observations
of these empty lakes have revealed a surface composition poor in water ice
compared to that of the surrounding terrains --- suggesting the existence of
organic evaporites deposits. The chemical composition of these possible
evaporites is unknown. In this paper, we study evaporite composition using a
model that treats both organic solids dissolution and solvent evaporation. Our
results suggest the possibility of large abundances of butane and acetylene in
the lake evaporites. However, due to uncertainties of the employed theory,
these determinations have to be confirmed by laboratory experiments.Comment: Icarus, in pres
Embedded density functional theory for covalently bonded and strongly interacting subsystems
Embedded density functional theory (e-DFT) is used to describe the electronic structure of strongly interacting molecular subsystems. We present a general implementation of the Exact Embedding (EE) method [J. Chem. Phys. 133, 084103 (2010)] to calculate the large contributions of the nonadditive kinetic potential (NAKP) in such applications. Potential energy curves are computed for the dissociation of Li^+–Be, CH_3–CF_3, and hydrogen-bonded water clusters, and e-DFT results obtained using the EE method are compared with those obtained using approximate kinetic energy functionals. In all cases, the EE method preserves excellent agreement with reference Kohn–Sham calculations, whereas the approximate functionals lead to qualitative failures in the calculated energies and equilibrium structures. We also demonstrate an accurate pairwise approximation to the NAKP that allows for efficient parallelization of the EE method in large systems; benchmark calculations on molecular crystals reveal ideal, size-independent scaling of wall-clock time with increasing system size
Using Satellites to Probe Extrasolar Planet Formation
Planetary satellites are an integral part of the heirarchy of planetary
systems. Here we make two predictions concerning their formation. First,
primordial satellites, which have an array of distinguishing characteristics,
form only around giant planets. If true, the size and duration of a planetary
system's protostellar nebula, as well as the location of its snow line, can be
constrained by knowing which of its planets possess primordial satellites and
which do not. Second, all satellites around terrestrial planets form by
impacts. If true, this greatly enhances the constraints that can be placed on
the history of terrestrial planets by their satellites' compositions, sizes,
and dynamics
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