Eclipse Measurements of Io's Sodium Atmosphere

The satellites of Jupiter eclipsed each other in 1985, and these events allowed an unusual measurement of the sodium in Io's extended atmosphere. Europa was used as a mirror to look back through the Io atmosphere at the sun. The measured column abundances suggest that the atmosphere is collisionally thin above 700 kilometers and may be collisionally thin to the surface. The sodium radial profile above 700 kilometers resembles a 1500 kelvin exosphere with a surface density near 2 x 10(4) sodium atoms per cubic centimeter, but a complete explanation of the dynamics requires a more complex nonthermal model: the calculated loss rates suggest that the atmosphere is being replaced on a time scale of hours.     

Stability of the martian atmosphere

A detailed chemical dynamic model is presented for a moist martian atmosphere. Recombination of carbon dioxide is catalyzed by trace amounts of water. The abundances of carbon monoxide and molecular oxygen should vary in response to changes in atmospheric water and atmospheric mixing.     

Comet encke: meteor metallic ion identification by mass spectrometer

Metal ions including 23(+) (Na(+)), 24(+) (Mg(+)) 28(+) (Si(+)), 39(+) (K(+)), 40(+) (Ca(+)), 45(+) (Sc(+)), 52(+) Cr(+)). 56(+) (Fe(+)), and 58(+) (Ni(+)) have been detected in the upper atmosphere during the period of the Beta Taurids meteor shower. The abundances of these ions relative to Si(+) show, agreement in most instances with abundances in chondrites. A notable exception is 45(+), which, if it is Sc(+), is 100 times more abundant than neutral scandium found in chondrites.     

Martian gases in an antarctic meteorite?

Significant abundances of trapped argon, krypton, and xenon have been measured in shock-altered phases of the achondritic meteorite Elephant Moraine 79001 from Antarctica. The relative elemental abundances, the high ratios of argon-40 to argon-36 (>/= 2000), and the high ratios of xenon-129 to xenon-132 (>/= 2.0) of the trapped gas more closely resemble Viking data for the martian atmosphere than data for noble gas components typically found in meteorites. These findings support earlier suggestions, made on the basis of geochemical evidence, that shergottites and related rare meteorites may have originated from the planet Mars.     

Venus lower atmospheric composition: preliminary results from pioneer venus

Initial examination of data from the neutral mass spectrometer on the Pioneer Venus sounder probe indicates that the abundances of argon-36, argon-38, and neon-20 in the Venus atmosphere are much higher than those of the corresponding gases in Earth's atmosphere, although the abundance of radiogenic argon-40 is apparently similar for both planets. The lower atmosphere of Venus includes significant concentrations of various gaseous sulfur compounds. The inlet leak to the mass spectrometer was temporarily blocked by an apparently liquid component of the Venus clouds during passage through the dense cloud layer. Analysis of gases released during the evaporation of the droplets shows the presence of water vapor to some compound or compounds of sulfur.     

Galileo infrared imaging spectroscopy measurements at venus

During the 1990 Galileo Venus flyby, the Near Infaied Mapping Spectrometer investigated the night-side atmosphere of Venus in the spectral range 0.7 to 5.2 micrometers. Multispectral images at high spatial resolution indicate substanmial cloud opacity variations in the lower cloud levels, centered at 50 kilometers altitude. Zonal and meridional winds were derived for this level and are consistent with motion of the upper branch of a Hadley cell. Northern and southern hemisphere clouds appear to be markedly different. Spectral profiles were used to derive lower atmosphere abundances of water vapor and other species.     

Helium on venus: implications for uranium and thorium

Helium is removed at an average rate of 10(6) atoms per square centimeter per second from Venus's atmosphere by the solar wind following ionization above the plasmapause. The surface source of helium-4 on Venus is similar to that on Earth, suggesting comparable abundances of crustal uranium and thorium.     

The atmosphere of Mars: detection of krypton and xenon

Krypton and xenon have been discovered in the martian atmosphere with the mass spectrometer on the second Viking lander. Krypton is more abundant than xenon. The relative abundances of the krypton isotopes appear normal, but the ratio of xenon-129 to xenon-132 is enhanced on Mars relative to the terrestrial value for this ratio. Some possible implications of these findings are discussed.     

Stratospheric nitrogen dioxide in the vicinity of soufriere, st. Vincent

In April 1979, measurements of nitrogen dioxide in the upper atmosphere were made near Soufriere Volcano by twilight optical-absorption techniques. The derived value of 5 x 10(15) molecules per square centimeter column implies an enhancement of 25 percent over earlier abundances measured in the same latitudinal regions. This enhancement may represent the normal stratospheric variability of nitrogen dioxide in the equatorial region but in any case may be considered an upper limit to the volcano's effect on the total nitrogen dioxide abundance.     

The Atmosphere of Mars near the Surface: Isotope Ratios and Upper Limits on Noble Gases

Several new analyses of the martian atmosphere have been carried out with the mass spectrometer in the molecular analysis experiment. The ratios of abundant isotopes of carbon and oxygen are within 10 percent of terrestrial values, whereas nitrogen-15 is considerably enriched on Mars. We have detected argon-38 and set new limits on abundances of krypton and xenon. The limit on krypton is sufficiently low to suggest that the inventories of volatile substances on Mars and on Earth may be distinctly different.     

Thermal spectrum of uranus: implications for large helium abundance

An analysis of the infrared spectrum of Uranus' disk between 7 micrometers and 3 millimeters suggests a volume mixing ratio for helium in the atmosphere of 40 +/- 20 percent, more than for the sun, Jupiter, or Saturn. Alternative explanations require even more extreme assumptions regarding gas abundances or aerosol vertical distribution and spectral properties. The most serious difficulty with a model containing large amounts of helium is devising a credible evolutionary or chemical model explaining the absence or segregation of so much hydrogen.     

Caloris Basin: An Enhanced Source for Potassium in Mercury's Atmosphere

Enhanced abundances of neutral potassium (K) in the atmosphere of Mercury have been found above the longitude range containing Caloris Basin. Results of a large data set including six elongations of the planet between June 1986 and January 1988 show typical K column abundances of approximately 5.4 x 10(8) K atoms/cm(2). During the observing period in October 1987, when Caloris Basin was in view, the typical K column was approximately 2.7 x 10(9) K atoms/cm(2). Another large value (2.1 x 10(9) K atoms/cm(2)) was seen over the Caloris antipode in January 1988. This enhancement is consistent with an increased source of K from the well-fractured crust and regolith associated with this large impact basin. The phenomenon is localized because at most solar angles, thermal alkali atoms cannot move more than a few hundred kilometers from their source before being lost to ionization by solar ultraviolet radiation.     

Vertical distribution of water in the atmosphere of venus: a simple thermochemical explanation

Several lines of evidence concerning the vertical abundance profile of water in the atmosphere of Venus lead to strikingly unusual distributions (the water vapor abundance decreases sharply in the immediately vicinity of the surface) or to serious conflicts in the profiles (different infrared bands suggest water abundances that are discrepant by a factor of 2.5 to 10). These data sets can be reconciled if (i) water molecules associate with carbon dioxide and sulfur trioxide to make gaseous carbonic acid and sulfuric acid in the lower atmosphere, and (ii) the discrepant 0.94-micrometer water measurements are due to gaseous sulfuric acid, requiring it to be a somewhat stronger absorber than water vapor inthis wavelength region. A mean total water abundance of 50 +/- 20 parts per million and a near-surface free water vapor abundance of 10 +/- 4 parts per million are derived.     

Origin and evolution of outer solar system atmospheres

The atmospheres of bodies in the outer solar system are distinct in composition from those of the inner planets and provide a complementary set of clues to the origin of the solar system. This article reviews current understanding of the origin and evolution of these atmospheres on the basis of abundances of key molecular species. The systematic enrichment of methane and deuterated species from Jupiter to Neptune is consistent with formation models in which significant infall of icy and rocky planetesimals accompanies the formation of giant planets. The atmosphere of the Saturnian satellite Titan has been strongly modified by photochemistry and interaction with the surface over 4.5 billion years; the combined knowledge of this moon's bulk density and estimates of the composition of the surface and atmosphere provide some constraints on this body's formation. Neptune's satellite Triton is a poorly known object for which it is hoped that substantial information will be gleaned from the Voyager 2 encounter in August 1989. The mean density of the Pluto-Charon system is well known and suggests an origin in the rather water-poor solar nebula. The recent occultation of a star by Pluto provides evidence that carbon monoxide, in addition to methane, may be present in its atmosphere.     

Jovian Atmosphere: Structure and Composition between the Turbopause and the Mesopause

The occultation of the star Beta Scorpii by Jupiter was observed at high time resolution in three wavelength channels. The results imply a temperature of 220 degrees K at an altitude in the Jovian atmosphere corresponding to 10(14) molecules per cubic centimeter, and temperature fluctuations of 2 degrees to 10 degrees K over vertical scales of 2 to 10 kilometers. They suggest that the vertical eddy diffusion coefficient near the turbopause has a lower limit of 7 x 10(5)K square centimeters per second, and that the turbopause lies above the altitude where the density is 5 x 10(13) molecules per cubic centimeter. Below the turbopause, the ratio of hydrogen to helium is consistent with cosmic abundances.     

High-Energy Charged Particles in the Innermost Jovian Magnetosphere

The energetic particles investigation carried by the Galileo probe measured the energy and angular distributions of the high-energy particles from near the orbit of Io to probe entry into the jovian atmosphere. Jupiter's inner radiation region had extremely large fluxes of energetic electrons and protons; intensities peaked at approximately2.2RJ (where RJ is the radius of Jupiter). Absorption of the measured particles was found near the outer edge of the bright dust ring. The instrument measured intense fluxes of high-energy helium ions (approximately62 megaelectron volts per nucleon) that peaked at approximately1.5RJ inside the bright dust ring. The abundances of all particle species decreased sharply at approximately1.35RJ; this decrease defines the innermost edge of the equatorial jovian radiation.     

Interstellar matter and chemical evolution

The determination of chemical abundances of the interstellar medium is related to three different areas of astronomy: pregalactic conditions, stellar evolution, and chemical evolution of galaxies. The observed abundances permit the testing of theories associated with these areas. Knowledge of the abundances of helium, carbon, nitrogen, and neon relative to the abundance of hydrogen in the interstellar medium puts limits on current models of cosmology, stellar evolution, and galactic evolution.     

Ages, irradiation history, and chemical composition of lunar rocks from the sea of tranquillity

The (87)Rb-(87)Sr internal isochrons for five rocks yield an age of 3.65 +/-0.05 x 10(9) years which presumably dates the formation of the Sea of Tranquillity. Potassium-argon ages are consistent with this result. The soil has a model age of 4.5 x10(9) years, which is best regarded as the time of initial differentiation of the lunar crust. A peculiar rock fragment from the soil gave a model age of 4.44 x 10(9) years. Relative abundances of alkalis do not suggest differential volatilization. The irradiation history of lunar rocks is inferred from isotopic measurements of gadolinium, vanadium, and cosmogenic rare gases. Spallation xenon spectra exhibit a high and variable (131)Xe/(126)Xe ratio. No evidence for (129)I was found. The isotopic composition of solar-wind xenon is distinct from that of the atmosphere and of the average for carbonaceous chondrites, but the krypton composition appears similar to average carbonaceous chondrite krypton.     

Greenhouse Effects due to Man-Mad Perturbations of Trace Gases

Nitrous oxide, methane, ammonia, and a number of other trace constituents in the earth's atmosphere have infrared absorption bands in the spectral region 7 to 14 microm and contribute to the atmospheric greenhouse effect. The concentrations of these trace gases may undergo substantial changes because of man's activities. Extensive use of chemical fertilizers and combustion of fossil fuels may perturb the nitrogen cycle, leading to increases in atmospheric N(2)O, and the same perturbing processes may increase the amounts of atmospheric CH(4) and NH(3). We use a one-dimensional radiative-convective model for the atmospheric thermal structure to compute the change in the surface temperature of the earth for large assumed increases in the trace gas concentrations; doubling the N(2)O, CH(4), and NH(3) concentrations is found to cause additive increases in the surface temperature of 0.7 degrees , 0.3 degrees , and 0.1 degrees K, respectively. These systematic effects on the earth's radiation budget would have substantial climatic significance. It is therefore important that the abundances of these trace gases be accurately monitored to determine the actual trends of their concentrations.     

Early differentiation of the Earth and the problem of mantle siderophile elements: a new approach

The long-standing problem of the excess abundances of siderophile elements in the mantle can be resolved by considering an equilibrium core-mantle differentiation in the earth at 3000 to 3500 kelvin. This high-temperature differentiation results in mantle siderophile element abundances that closely match the observed values. Some lithophile (light) elements could enter the core in this process as is necessary to account for its low density. The abundances of siderophile elements in the mantle are consistent with the conclusion derived from the recent physical models that the earth was molten during accretion.