Photochemistry of Planetary Atmospheres

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94723/1/eost12487.pd

Book Review: Physics and Chemistry of the Upper Atmosphere

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94675/1/eost8433.pd

Giant planets: Clues on current and past organic chemistry in the outer solar system

The giant planets of the outer solar system - Jupiter, Saturn, Uranus, and Neptune - were formed in the same flattened disk of gas and dust, the solar nebula, as the terrestrial planets were. Yet, the giant planets differ in some very fundamental ways from the terrestrial planets. Despite enormous differences, the giant planets are relevant to exobiology in general and the origin of life on the Earth in particular. The giant planets are described as they are today. Their basic properties and the chemistry occurring in their atmospheres is discussed. Theories of their origin are explored and aspects of these theories that may have relevance to exobiology and the origin of life on Earth are stressed

Eddy mixing coefficient on Saturn

Data on the composition and thermal structure, and the Lyman-alpha dayglow of Saturn when analyzed in conjunction with photochemical models of the hydrocarbons and the atomic hydrogen production yield the homopause value of the eddy diffusion coefficient to be approximately 108 cm2 s-1. The equatorial value of the eddy diffusion coefficient at the homopause of Saturn is thus found to be approximately 100 times greater than on Jupiter. The mesosphere (and presumably, troposphere) of Saturn appears to be considerably more turbulent than the upper atmosphere of Jupiter.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23919/1/0000164.pd

Hydrocarbons and eddy mixing in Neptune's atmosphere

The most recent analysis of the Voyager ultraviolet solar occultation observations at Neptune indicates a methane mixing ratio 1-10 times above saturation in the lower stratosphere, unlike the value of 500-1000 times saturation which was suggested just before the encounter of Voyager with Neptune. The acetylene mixing ratio in the 0.1 mb region is found to be (6-8) x 10-8, which is approximately a factor of 3 lower than the value reported in our Voyager/Science paper. The eddy diffusion coefficient at the homopause, (1-3) x 107 cm2 s-1, is found to be more like that on Saturn than Uranus. The new results on CH4, C2H2 and K have strong implications for the stratospheric temperatures, now warmer, and the source of heating. Furthermore, the pre-Voyager models of the hydrocarbon hazes need to be revised in view of the new model atmosphere.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/29737/1/0000073.pd

Uranus photochemistry and prospects for Voyager 2 at Neptune

Methane is the only photochemically active constituent in the atmospheres of Uranus and Neptune. NH3, H2O and H2S are all removed by condensation at pressures greater than 1.5 bars. Although the bulk mole fraction (~2%) of CH4 is 20-30 times its solar value on both planets, it drops to its saturation limit (~ 10-4) at the Uranus tropopause, but remains high (~2%) at the Neptune tropopause. This results in much greater mixing ratios of the product hydrocarbons (ethane, acetylene, ethylene and polyacetylenes) in the stratosphere of Neptune. On both planets, the photolysis products of methane undergo condensation near the tropopause and the upper stratosphere. Voyager observations of the hydrocarbons at Uranus, and those planned at Neptune will be discussed, along with their implications for the upper atmospheric physics and thermochemistry.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28808/1/0000642.pd

Stratospheric aerosols from CH 4 photochemistry on Neptune

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95495/1/grl4442.pd

Measurement of minor species (H2, Cl, O3, NO) in the earth's atmosphere by the occultation technique

The stellar occultation technique is a clean and powerful means of detecting and quantifying minor gases in the earth's atmosphere. The results obtained are totally insensitive to knowledge of the absolute flux of the star, and are not influenced by instrument calibration problems. Pioneering observations of nocturnal mesospheric ozone and thermospheric molecular oxygen by the stellar occultation technique were made in 1970 and 1971 with the Wisconsin stellar photometers on board the Orbiting Astronomical Observatory-2. A limb crossing geometry was used. The high resolution Princeton ultraviolet spectrometer aboard Copernicus was used in the summers of 1975, 1976 and 1977 to measure altitude profiles of molecular hydrogen, atomic chlorine and nitric oxide in addition to ozone and molecular oxygen. A limb grazing geometry was employed. The ozone densities show wide variation from orbit to orbit and particularly betewen the OAO-2 and Copernicus observations. A H2 density of 1 x 108 cm-3 at 95 km, and a NO density less than 106 cm-3 for altitudes greater than 85 km were measured.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/24516/1/0000794.pd

Saturn's Exploration Beyond Cassini-Huygens

For its beautiful rings, active atmosphere and mysterious magnetic field, Saturn is a fascinating planet. It also holds some of the keys to understanding the formation of our Solar System and the evolution of giant planets in general. While the exploration by the Cassini-Huygens mission has led to great advances in our understanding of the planet and its moons, it has left us with puzzling questions: What is the bulk composition of the planet? Does it have a helium core? Is it enriched in noble gases like Jupiter? What powers and controls its gigantic storms? We have learned that we can measure an outer magnetic field that is filtered from its non-axisymmetric components, but what is Saturn's inner magnetic field? What are the rings made of and when were they formed? These questions are crucial in several ways: a detailed comparison of the compositions of Jupiter and Saturn is necessary to understand processes at work during the formation of these two planets and of the Solar System. This calls for the continued exploration of the second largest planet in our Solar System, with a variety of means including remote observations and space missions. Measurements of gravity and magnetic fields very close to the planet's cloud tops would be extremely valuable. Very high spatial resolution images of the rings would provide details on their structure and the material that form them. Last but not least, one or several probes sent into the atmosphere of the planet would provide the critical measurements that would allow a detailed comparison with the same measurements at Jupiter. [abridged abstract

Clouds of Neptune and Uranus

We present results on the bases and concentrations of methane ice, ammonia ice, ammonium hydrosulfide-solid, water ice, and aqueous-ammonia solution (droplet) clouds of Neptune and Uranus, based on an equilibrium cloud condensation model. Due to their similar p-T structures, the model results for Neptune and Uranus are similar. Assuming 30-50x solar enhancement for the condensibles species, as expected from formation models, we find that the base of the droplet cloud is at the 370 bars for 30 solar, and at 500 bars for 50 solar cases. Despite this, entry probes need to be deployed to only 50-100 bars to obtain all the critical information needed to constrain models of the formation of these planets and their atmospheres