Atmosphere of Uranus

Diacetylene (HC=C—C=CH) has been identified as a component of the hydrocarbon rich atmospheres of Uranus Neptune and Pluto It is also present m the atmospheres of Titan and Triton satellites of Saturn and Neptune respectively... 

G. Herzberg. Spectroscopic evidence of molecular hydrogen in the atmospheres of uranus and neptune. Astrophys. J., 115 337, 1952. 

Table IX. Chemical Composition of the Atmospheres of Uranus and Neptune...

Abstract. We present a historical review of polarimetric observations of planetary atmospheres, comets, atmosphereless solar system bodies, and terrestrial materials. We highlight the study of physical and optical parameters of planetary atmospheres. Polarimetric observations of the atmospheres of Venus, Mars, Jupiter and Saturn have made it possible to determine the real part of the refractive index and the cumulative size distribution function for the constituent cloud layers. We describe a simple and reliable method of quantifying absorptive cloud layers of the giant planets and predict the vertical stracture of aerosol layers of planetaiy atmospheres based on the analysis of observational spectropolarimetric data of contours of molecular absorption bands at the center of the planetaiy disk. The method is effective only when experimental data exist in a broad interval of phase angles. Using this method we can determine aerosol sizes in the atmospheres of Uranus and Neptune. 

The rotational lines of ammonia (NH3) below 250 cm can easily be identified in the Jovian spectrum, but they are less prominent on Saturn, and completely absent on Uranus and Neptune. A comparison of the vapor pressure curve of NH3 with the ambient temperatures on these planets indicates that the atmospheres of Uranus and Neptune are just too cold to contain much NH3 in gaseous form at the pressure levels pertinent to these measurements, that is, at pressures up to about one bar. If NH3 were pushed up with a pocket of gas from lower levels, it would first supercool and, eventually, form small ice crystals. Earth-based measurements of the microwave... 

Fegley, B., Gautier, D., Owen, T., Prinn, R. G. (1991). Spectroscopy and chemistry of the atmosphere of Uranus. In Uranus, 147-203, ed. J. Bergstralh, E. Miner, M. S. Matthews. Tucson University of Arizona Press. 

Lindal, G. R, Lyons, J. R., Sweetnam, D. N., Eshleman, V. R., Hinson, D. R, Tyler, G. L. (1987). The atmosphere of Uranus results of radio occultation measurements with Voyager 2. Journal of Geophysical Research, 92,14987-5001. 

The atmosphere of Uranus consists of a troposphere followed by a stratosphere and a thermosphere. 

Uranus The temperature in the Uranus atmosphere, which consists of molecular hydrogen containing around 12% helium, is close to 60 K. A methane cloud layer has been detected in the lower layers of this atmosphere. The planet is surrounded by a magnetosphere which extends into space for about ten times the diameter of Uranus. The planet has 27 moons of various sizes and is surrounded by a ring system which consists of thin dark rings. The planet is unusual in two respects its tilted axis and retrograde rotation. 

Alkanes are often found in natural systems. They are the main constituents in the atmospheres of the planets Jupiter, Saturn, Uranus, and Neptune. Methane is also thought to have been a major component of the atmosphere of the early Earth. Natural gas and oil are primarily made of alkanes. 

Aspects of the chemical composition of the atmospheres of Jupiter, Saturn, Uranus, and Neptune were measured by the Voyager and Galileo spacecraft in the 1980s and 1990s,... 

Hydrogen isotopic compositions, expressed as molar D/H ratios, of solar system bodies. The relatively low D/H values in the atmospheres of Jupiter and Saturn are similar to those in the early Sun, whereas D/H ratios for Uranus and Neptune are intermediate between the Jupiter-Saturn values and those of comets and chondrites. The Earth s oceans have D/H shown by the horizontal line. Mars values are from SNC meteorites. Modified from Righter et al. (2006) and Lunine (2004). 

It is, therefore, noteworthy that almost immediately upon Welsh and associates discovery of collision-induced absorption in hydrogen [128, 129, 420], Herzberg found the first direct evidence of the H2 molecule in the atmospheres of the outer planets [181, 182], He was able to reproduce in the laboratory the unidentified diffuse feature at 827.0 nm observed by Kuiper in the spectra of Uranus and Neptune, using an 80 m path of hydrogen at 100 atmospheres pressure and a temperature of 78 K. The feature is the S3(0) line of the 3 — 0 collision-induced rotovibrational band of the H2 molecule [182]. 

Herzberg was able to point out another line at 816.6 nm which he identified as a double transition, partially overlapped by an adjacent CH4 band in the Uranus spectra. In the laboratory spectra recorded with unmixed hydrogen, this double transition was relatively strong, but in the photographic plates of Uranus the feature was much weaker relative to the S3(0) line. This observation led Herzberg to conclude that sizeable He concentrations exist in these atmospheres (albeit the estimates of [He] [H2] abundance ratio seem high), because the S3(0) feature is enhanced by the presence of He, but H2-He pairs cannot undergo double transitions these features thus appear weak in Kuiper s plates relative to the S3(0) feature. 

Several applications of IR spectroscopy to astrophysics have been made. Small amounts of methane in the earth s atmosphere have been detected by the observation of weak IR absorption lines in solar radiation that has passed through the earth s atmosphere. Intense IR absorption bands of CH4 have been found in the spectra of the atmospheres of Jupiter, Saturn, Uranus, and Neptune. Bands of ammonia have been observed for Jupiter and Saturn bands of C02 have been observed in the Venusian spectrum and bands of H20 have been observed in the Martian spectrum. 

A child on the planet Uranus would ask the question, Why is the sky green A child on Jupiter would ask the question, Why is the sky reddish brown How would you answer these questions Relate your answer to the chemical composition of the atmospheres of these planets. 

The chemical dynamics, reactivity, and stability of carbon-centered radicals play an important role in understanding the formation of polycyclic aromatic hydrocarbons (PAHs), their hydrogen-dehcient precursor molecules, and carbonaceous nanostructures from the bottom up in extreme environments. These range from high-temperature combustion flames (up to a few 1000 K) and chemical vapor deposition of diamonds to more exotic, extraterrestrial settings such as low-temperature (30-200 K), hydrocarbon-rich atmospheres of planets and their moons such as Jupiter, Saturn, Uranus, Neptune, Pluto, and Titan, as well as cold molecular clouds holding temperatures as low as 10... 

A more likely scenario is that Uranus and Neptune, along with the cores of Jupiter and Saturn, formed in the region 5-10 AU from the Sun. Such a system would have remained dynamically stable until one object (Jupiter) accreted a large H/He-rich atmosphere. At this point at least two of the other bodies would have been permrbed into the region beyond 15 AU. Gravitational interactions with planetesimals in the outer solar system would then have circularized the orbits of Uranus and Neptune by dynamical friction, while at the same time scattering most of these planetesimals onto... 

The temperature at the aerosol layer in Neptune s atmosphere is about -346°F (-210°C), which is close to the temperature at the main cloud level in Uranus s atmosphere, and the effective temperatures of the atmospheres of both Uranus and Neptune were found to be close to this temperature. One would expect Neptune s visible troposphere and lower stratosphere to be about 59°F (15°C) colder than those of Uranus because of Neptune s greater distance form the Sun (30.1 a.u. vs. 19.2 a.u.) instead, the temperatures of these parts of the atmospheres of both planets are found to be about the same. Neptune s atmosphere seems to be considerably warmer than it would be if it received all or nearly all its heating from sunlight, as seems to be the case for Uranus. This is another indication that Neptune has a powerful internal heat source, unlike Uranus, which has at most a weak internal heat source (compatible with radioactivity in its interior) or none at all. Voyager 2 infrared observations confirmed this the emission to insolation ratio was found to be 2.6 from them instead of... 

Neptime s atmosphere was found to be similar to that of Uranus in that it seems to have little temperature change with latitude. This probably indicates enormous heat capacities for both atmospheres. Also Neptune has a hot (about 900 F [482 C]) ionosphere and an exosphere that consists mainly of a hydrogen thermal corona both these atmospheric components seem similar to those of Uranus. However, Neptune s stronger gravity and slightly colder stratosphere cause much lower particle densities in Neptune s upper atmosphere than are found at the same heights above the cloud layers in Uranus s atmosphere. 

---