Icarus
We model an infrared outburst on Io as being due to a large, erupting lava flow which increased its area at a rate of 1.5 x 10 5 m 2 sec - 1 and cooled from 1225 to 555 K over the 2.583-hr period of observation. The inferred effusion rate of 3 x 10 5 m 3 sec - 1 for this eruption is very high, but is not unprecedented on the Earth and is similar...
On 13 December 1989, Jupiter occulted a star with visual magnitude 8.7 and an estimated K magnitude of 7. We observed the event from Kitt Peak, Arizona, using a 64 x 64 infrared camera at a wavelength of 2.16 μm. The resulting data on refractive defocusing of the stellar signal give information on the temperature of the jovian atmosphere at pressures ~2 to 10 μbar, at near-equatorial latitudes. These...
The Pioneer Venus Orbiter Ultraviolet Spectrometer measurements of the Lyman-α intensity of atomic hydrogen excited by solar resonance scattering in the coma of Comet P/Halley acquired from December 28, 1985, to January 6, 1986, and from January 31, 1986, to March 6, 1986, are simulated with the Monte Carlo Particle Trajectory Model corrected for optical depth effects. Spatially detailed comparisons...
The limb to limb Lyman-α reflectivities observed with the Voyager UVS instruments during the fly-by of Saturn are reanalyzed using a revised H Lyman-α sensitivity for the Voyager 1 instrument. The new sensitivity reconciles the measured intensities to those of Voyager 2 and gives a coherent set of data. To fit the UV airglow observations, four sources are considered: (i) H resonance and H 2 ...
The identification of the mechanism(s) responsible for heating asteroids is among the major problems in planetary science. Because of difficulties with models of electromagnetic induction and the decay of short-lived radionuclides, it is worthwhile to evaluate the evidence for collisional heating. Localized impact heating is responsible for forming shock veins, melt pockets, metal-sulfide mixtures,...
The Voyager 2 Photopolarimeter experiment has yielded the highest resolved data of Saturn's rings, exhibiting a wide variety of features. The B-ring region between 105,000 and 110,000 km from Saturn has been investigated. It has a high matter density and contains no significant features visible by eye. Analysis with statistical methods has led us to the detection of two significant events. These features...
A simple formalism is presented that permits quick computations of the low-resolution, rotovibrational collision-induced absorption (RV CIA) spectra of H 2 pairs in the first overtone band of hydrogen, at temperatures from 20 to 500 K. These spectra account for the free-free transitions. The sharp dimer features, originating from the bound-free, free-bound, and bound-bound transitions are...
Titan's large free eccentricity results in significant tidal dissipation. This can be used to constrain the existence and depth of hydrocarbon oceans. A hydrodynamical-numerical 2 o ocean tide model has been constructed to investigate this connection. The model allows some simple land configurations. The results indicate that existence of such an ocean over the age of the solar system is hard...
Recent high-resolution 2.10- to 2.13-μm equatorial spectra of Jupiter show several prominent absorption lines in addition to a narrow H 2 1-0 S(1) absorption. Comparison with laboratory spectra of the H 2 dimer reveals excellent wavelength coincidences with five of the jovian absorptions. We conclude that the jovian lines are due to the H 2 dimer. No other jovian lines are...
We present observations of Saturn's central flash obtained from Palomar and McDonald Observatories during the 3 July 1989 occultation of 28 Sgr. As the star passed close to the geometric center of Saturn's shadow, the focusing of the incident starlight by the planet's atmosphere formed multiple stellar images along the limb which were detected in infrared images obtained at wavelengths of 3.9 (Palomar)...
We have developed a new photochemical model of Titan's atmosphere which includes all the important compounds and reactions in spherical geometry from the surface to 1240 km. Compared to the previous model of Yung et al. (1984, Astrophys. J. Suppl. 55, 465-506), the most significant recent change in the reactions used is the updated methane photodissociation scheme (Mordaunt et al. 1993, J. Chem. Phys...
UBVRI polarimetric observations of NEA 4179 Toutatis were carried out at the Crimean Astrophysical Observatory for six nights in December 1992-January 1993. Phase curves of polarization over the phase angle range 15.8-51.4 o were obtained in each photometric band. Spectral dependences of positive polarization, polarimetric slope h, and inversion angle α i n v in UBVRI wavelength...
The efficacy of the UV reflectance spectroscopy technique used by Mariner 9 to remotely measure ozone abundance at Mars is discussed. Due to temporal and spatial variability in cloud and dust amount, previously inferred ozone abundances could be underestimated by a factor of 3. Until the large uncertainty in cloud and dust scattering properties and opacities can be reduced, the ozone abundance inferred...
Most asteroid dynamical families are thought to be the outcomes of collisional disruption of parent asteroids destroyed by high-velocity impacts with other astroids. However, subsequent collisions modify both the sizes and the orbits of family members, so the distributions that we see today may be very different from those following the breakup of the parent body. We study the postbreakup evolution...
A close examination of the 0.7- to 23-μm infrared data base acquired by Gehrz and Ney (1992, Icarus 100, 162-186) suggests that the nucleus of Comet P/Halley 1986 III emitted a burst of small dust grains during a 3-day period commencing within hours of perihelion passage on 1986 February 9.46 UT. The outburst was characterized by significant increases in the coma's grain color temperature T o...
Recent observations demonstrate that near-infrared spectroscopy can probe Titan's surface through its haze. In a 5-week period during September and October 1993 we observed Titan's methane windows at 1.1, 1.3, 1.6, and 2 μm. At 1.1 and 1.3 μm observations were consistent with observations in 1992 at the same phases reported by Lemmon et al. (1993, Icarus 103, 329-332). Our new observations indicate...
The 183-GHz water vapor line was tentatively detected on Mars in January 1991, with the IRAM 30-m millimeter antenna, under extremely dry atmospheric conditions. The measurement refers to the whole disk. The spectral line, although marginally detected, can be fit with a constant H 2 O mixing ratio of 1.0 x 10 - 5 , which corresponds to a water abundance of 1 pr-μm; in any case,...
The intensity and polarization of light scattered by a variety of types of artificial particles large compared to the wavelength were measured as a function of phase angle. Shape, surface roughness, absorption coefficient, and internal scattering coefficient were varied systematically and their effects studied. Scattering by clear, smooth-surfaced spheres is in quantitative agreement with the predictions...
Both Saturn's rings and planetesimal disks are made up of particles in Keplerian orbits. Inelastic collisions between these particles regulate their dynamical evolution and possible aggregation. We present an experiment to simulate glancing collisions in Saturn's rings and in planetesimal disks and thus measure contributions to the energy loss for both normal and tangential velocity components. In...