Seasonal change of CH4/H2 ratio in the atmosphere of Uranus
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Uranus is mainly composed of elements heavier than hydrogen and helium, such as C, S, even though very little information about these elements has been detected. Methane is one of the most important component of the atmosphere of Uranus. Analysis of the full-disk spectra of Uranus, as observed by the Xinglong 2.16m telescope with BFOSC (Beijing-Faint Object Spectrograph and Camera) on August 26 2016, was performed. A simple empirical model was used to fit the several years of spectrum albedo data to determine the variations of the CH4/H2 ratio in the atmosphere of Uranus. These data include: spectra observed by the 1.52m telescope (1994 and 1995) on La Silla, Chile; spectra observed by the HST-STIS (2002 and 2003); and spectra observed by the Xinglong 2.16m telescope (2016). The interannual change of the CH4/H2 ratio can be derived by comparing the fit results of various spectral albedos. The comparative results indicate that the CH4/H2 ratio in the atmosphere of Uranus declined from 1994 until 2002, and then began to rise thereafter. From the results, we speculate that the variation period of CH4/H2 ratio in the atmosphere of Uranus is longer than twenty years. We were unable to confirm whether the period is 84 or 42 years.
KeywordsPlanets and satellites: atmospheres Planets and satellites: composition Planets and satellites: gaseous planets Telescopes: Instrumentation: spectrographs Planets and satellites: individual: Uranus
This work was supported by the Strategic Research Program of Chinese Academy of Sciences, Grant No. XDA17010301 and the National Natural Science Foundation of China (41204137). We acknowledge the support of the staff of the Xinglong 2.16m telescope. This work was partially supported by the Open Project Program of the Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences. We thank Professor Ding Chen who provided constructive suggestions for improving this work.
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