For Uranus

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). 

To the accuracy of the measurement of molecular weights for the giant planets, only hydrogen and helium have significant abundances. The relative proportions of these elements, expressed as the molar fraction He/H, are 0.068+0.002 for Jupiter, 0.068+0.013 for Saturn, 0.076+0.016 for Uranus, and 0.100+0.016 for Neptune (Lunine, 2004). None of these ratios are like those of the nebula (0.085, Table 4.1). 

The temperature profiles within Jupiter and Saturn are thought to be essentially adiabatic, reflecting the high central temperatures and the dominant role of convection below the observable atmosphere where radiative processes become important. There may be deeper layers restricted in radial extent where the temperature profile becomes subadiabatic, due to a decrease in the total opacity, or by virtue of the behavior of the equation of state of hydrogen and helium. The same may hold for Uranus and Neptune, although with less certainty, because of the possibility that stable compositional gradients could exist and dominate the heat flow regime. In particular, Uranus small heat flow, if primordial and not a function of seasonal insolation, could be the result of a stable compositional stratification and hence subadiabatic temperature profile in the interior (Podolak et al., 1991). 

From Triton s 5.866 day period of revolution around Neptune and its 220,000 mi (354,300 km) mean distance from it, astronomers estimated Neptune s mass to be 17.14 Earth masses, according to Kepler s third law. From Neptune s mean radius of 15,290 mi (24,625 km), a mean density (mass divided by volume) of 1.64 grams/cm was found. These values are similar to the ones found for Uranus. Uranus is slightly larger than Neptune, but Neptune is considerably more massive and denser than Uranus. Thus, Neptune is one of the Jovian planets, which are characterized by large sizes and masses but low mean densities (compared with Earth). The last characteristic implies that Jovian planets have extremely thick atmospheres and are largely or mostly composed of gases. 

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... 

Like the case for Uranus s rings, the origin and evolution of Neptune s rings are unknown. Are they the result of earlier tidal disruption of other nearby satellites Are they a transitory phenomenon, or will they persist for millions or billions of years Comparison of the positions of the arcs in the Adams ring observed by Voyager 2 in 1989 with their positions extrapolated back in time to 1984 and 1985 shows that they match the positions of three occultations of stars observed in those years. This indicates that the arcs in the Adams ring are stable over time intervals of at least five years. 

Seaborg s team suggested the name plutonium for the new element, in honor of the planet Pluto. The two elements just before plutonium in the periodic table had also been named for planets uranium for Uranus and neptunium for Neptune. 

It takes 84 years — a human lifetime — for Uranus and its 15 moons to travel through the zodiac. Like Jupiter, Saturn, and Neptune, Uranus is a gas giant. But while every other planet rotates on its axis in a more-or-less upright fashion, unconventional Uranus seems to roll around on its side with its north pole pointing to the Sun. As a result, the Uranian day is 42 years long, and the night is the same length. 

The four giant planets have hydrogen- and helium-rich compositions reminiscent of the Sun, but all of them clearly depart from strict solar composition in that their densities are too high and the few heavier elements whose tropospheric abundances can be measured all show clear evidence of enrichment. For all four giant planets we have spectroscopic compositional data on the few compounds that remain uncondensed in the visible portion of their atmospheres, above their main cloud layers. These include ammonia, methane, phosphine, and germane. For Jupiter, these volatile elements (C, N, S, P and Ge) are enriched relative to their solar abundances by about a factor of five. For Saturn, with no detection of germane, the enhancement of C, N, and P is about a factor of 10. For Uranus and Neptune the methane enrichment factor is at least 60, consonant with their much higher uncompressed densities. 

Currently, LFR R D in ROK is focused on the further development of computer codes and corrosion-resistant materials as weU as the safety design criteria. System design codes for URANUS have been focused on neutronic models and safety analysis codes. It is planned that the developed codes will be verified by independent experts. Thermomechanical processing of corrosion-resistant materials developed for long-life core will be explored to achieve desirable combinarion of proven mechanical properties in fast neutron environment and innovalive corrosion resistance. The ROK LFR R D community has been participating in the GIF LFTi provisional Systems Steering Committee as an observer. It is planned that the safety design criteria for URANUS will be derived from the international collaboration. 

On Uranus and Neptune temperatures in the upper troposphere are low enough for the formation of CH4 clouds. To obtain the CH4 concentration representative of the atmosphere as a whole the CH4 abundance below the CH4 cloud deck must be determined. Fortunately, this was possible for Uranus from data obtained by the Voyager Radio Science Investigation (Lindal et al, 1987) and from ground-based microwave measurements (Lutz et al., 1976). Scattering within the clouds complicates the interpretation of ground-based near infrared measurements. 

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