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[en] The following physical parameters were calculated for the atmosphere of Titan, using Voyager's measurements: 1) Temperature, 2) Pressure, 3) Density, 4) Speed of sound, 5) Density scale, 6) Number density, 7) Mean free path, 8) Viscosity, 9) Pressure scale, 10) Mean particle velocity, 11) Mean collisional frequency, 12) Columnar mass. (author). 12 figs., 2 tabs., 18 refs
[en] The March 3, 1987 occultation of Charon by Pluto was observed spectroscopically from 5400 to 10,200 A at a resolution of 12 A. The midpoint of the event occurred at 11:06 UT; the depth of the event at 6800 A was 0.162 mag. The spectrum of Charon is completely featureless and almost perfectly flat; the red slope and the CH4 absorption features can be attributed solely to Pluto. 17 references
[en] MeV-energy He beams from a van de Graaff accelerator are used to experimentally assess the problem of sulfur sputtering on Io. It is possible, assuming uniform sulfur coverage and using the inferred ion fluxes together with the experimentally determined sputtering yields, to evaluate the erosion rates and compare them with those expected on the basis of sublimation. While sputtering dominates sublimation in material removal, sputtering cannot be the sole supply of neutral sulfur for the Io torus. 25 references
[en] After some introductory discussions about morphological concepts and limitations of various measurement techniques, existing low energy plasma data, orginating primarily from the GEOS, Dynamics Explorer, and Prognoz spacecraft, is described and discussed. The plasmasphere measurements are not included (but for some observations of plasmasphere refilling). It is finally concluded that we are very far from a complete picture of the low-energy plasma component in the magnetosphere and that this problem has to be given high priority in planning payloads of future space plasma physics missions. (Author)
[en] Hot Jupiters receive strong stellar irradiation, producing equilibrium temperatures of . Incoming irradiation directly heats just their thin outer layer, down to pressures of ∼0.1 bars. In standard irradiated evolution models of hot Jupiters, predicted transit radii are too small. Previous studies have shown that deeper heating—at a small fraction of the heating rate from irradiation—can explain observed radii. Here we present a suite of evolution models for HD 209458b, where we systematically vary both the depth and intensity of internal heating, without specifying the uncertain heating mechanism(s). Our models start with a hot, high-entropy planet whose radius decreases as the convective interior cools. The applied heating suppresses this cooling. We find that very shallow heating—at pressures of —does not significantly suppress cooling, unless the total heating rate is of the incident stellar power. Deeper heating, at 100 bars, requires heating at only 1% of the stellar irradiation to explain the observed transit radius of after 5 Gyr of cooling. In general, more intense and deeper heating results in larger hot-Jupiter radii. Surprisingly, we find that heat deposited at —which is exterior to of the planet’s mass—suppresses planetary cooling as effectively as heating at the center. In summary, we find that relatively shallow heating is required to explain the radii of most hot Jupiters, provided that this heat is applied early and persists throughout their evolution.
[en] Hot Jupiters, with atmospheric temperatures T ∼> 1000 K, have residual thermal ionization levels sufficient for the interaction of ions with the planetary magnetic field to result in a sizable magnetic drag on the (neutral) atmospheric winds. We evaluate the magnitude of magnetic drag in a representative three-dimensional atmospheric model of the hot Jupiter HD 209458b and find that it is a plausible mechanism to limit wind speeds in this class of atmospheres. Magnetic drag has a strong geometrical dependence, both meridionally and from the dayside to the nightside (in the upper atmosphere), which could have interesting consequences for the atmospheric flow pattern. By extension, close-in eccentric planets with transiently heated atmospheres will experience time-variable levels of magnetic drag. A robust treatment of magnetic drag in circulation models for hot atmospheres may require iterated solutions to the magnetic induction and Saha equations as the hydrodynamic flow is evolved.
[en] The depth of penetration of Jupiter's zonal winds into the planet's interior is unknown. A possible way to determine the depth is to measure the effects of the winds on the planet's high-order zonal gravitational coefficients, a task to be undertaken by the Juno spacecraft. It is shown here that the equatorial winds alone largely determine these coefficients which are nearly independent of the depth of the non-equatorial winds