Research Of Spectroscopic Observations On The Atmosphere Of Ice Giant Planet

The giant planets being mainly composed of elements heavier than hydrogen and helium are defined as ice giant planets.The Uranus and Neptune are two typical ice giant planets in the solar system.We carried out the new observations at Xinglong Observatory of the National Astronomical Observatories,Chinese Academy of Sciences,and Lijiang Observatory of Yunnan Observatories,Chinese Academy of Sciences,during the three nights of August,2016.The observations of Xinglong Observatory were made with the 2.16m telescope using the BFOSC(Bao Faint Object Spectrograph and Camera),which has a spectral range from 385 to 900nm,on 26 August,2016.The observations of Lijiang Observatory were made with the 2.4m telescope using the YFOSC(Yunnan Faint Object Spectrograph and Camera),which has a spectral range from 320 to 983nm,on 18 and 19 August,2016.During August,2016,Lijiang 2.4 telescope's YFOSC was used to obtain two consecutive days of the Uranian spectra and the Neptune's spectra,in order to study meridional change.The observation time interval between the spectrum observated in 18 August and 19 August is about one and a half ratation period of the Uranus and Neptune.Hence,we can determine the variation of Uranus's and Neptune's atmosphere with longitude by comparing two consecutive days of the spectra.The comparison of two consecutive days of spectra indicates that the compitions in Uranus's atmosphere are almost unchanged with longitude.It is possible that the zonal wind of the Uranus,which can reach the maximum 273m/s,leads to the atmosphere being uniform with longitude.In order to determine the seasonal variations of Uranian full disk reflectivity,we used a simple model to fit the many years of spectral albedo.These data include the spectra(1994 and 1995)observated by 1.52m telescope at ESO,on La Silla,Chile,the spectra(2002 and 2012)observated by Hubble Space Telescope with STIS,and the spectra observated by Xinglong 2.16m telescope.The model result indicates that the ratio of CH4 to H2 of Uranian atmosphere kept declining form 1994 until 2002,and then the ratio began to rise.But we couldn't confirm the inflection point of variation due to the absence of the spectra observated on 2007,when the Uranus passed the equinox.From the results,we can speculate that the variation period of the Uranian atmosphere longer than twenty years.