Ammonia cloud composition

Jupiter and Uranus are outer planets composed mainly of gases. Jupiter s atmosphere contains reddish-brown clouds of ammonia. Uranus has an atmosphere made up mainly of hydrogen and helium with clouds of water vapor. This combination looks greenish to an outside observer. In addition, Mars has an atmosphere that is 95% carbon dioxide, and Venus has a permanent cloud cover of sulfur dioxide that appears pale yellow to an observer. Mercury has no permanent atmosphere. Saturn has 1 km thick dust and ice rings that orbit the planet. The eight planets in our solar system are diverse, each having different chemical compositions within and surrounding the planets. Out Earth is by far the friendliest planet for human existence. 

The composition of these thin clouds appears to be consistent with earlier suggestions that they consist of ammonia ice (at 0.5 bar), ammonium hydrosulflde (NH4SH) ice (at 1.3 bar), and water ice (at 1.6 bar). 

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. 

Knowledge of the composition of fhe interstellar medium has been growing rapidly in the last 25 years. Spectroscopic techniques, including some that will be considered in Chapter 10, can sometimes reveal the "fingerprints" of molecules in the electromagnetic radiation received from interstellar space. In 1963 the existence of OH was reported, and in 1968 Charles Townes and coworkers identified the first polyatomic molecule, ammonia, in a cloud associated with the constellation Sagittarius. The next year water was identified, and Lewis Snyder found the first organic molecule, formaldehyde. Today, there are over 100 molecules and molecular ions that have been detected in space. 

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