0 Assigned ID: 696 ----- Attempting Submission 1 (Fri Mar 06 19:30:55 GMT 2020) ----- This archival research program will be to reduce, analyze and model Lyman alpha emissions from the exosphere of Uranus conducted between 1996 to 2017. The goal is to study the evolution of Uranus' exosphere as it traversed in its orbit around the Sun. An initial reduction of the 1998 data shows Lyman alpha emission up to 5 Uranus radii (127795 km). Uranus' thermospheric temperature has been observed to decrease with time since 1990. The effect of this steady cooling on its exospheric density distribution and escape will be determined using the archived HST observations. This will allow for a better understanding of the dust environment, essential for planning future Ice Giant missions. At present, there is no general understanding of Uranus' exosphere and its evolution with seasons as no studies have been conducted after the intial Voyager 2 visit. The archived set of observations as well as the existence of an in-house radiative transfer model which can simulate optically thick Lyman alpha emissions from planetary H exospheres, provides the perfect opportunity to bridge this knowledge gap. Under the proposed program, data from HRS, STIS and ACS will be used and an updated calibration factor for ACS at Lyman alpha and a STIS Lyman alpha flatfield will be applid to the data reduction process. The radiative transfer model will then be used to simulate the Lyman alpha emissions from Uranus' exosphere in order to determine its characteristics. PI Dolon Bhattacharyya is experienced in radiative transfer theory and is the developer of the radiative transfer model that has been extensively used to simulate resonantly scattered solar Lyman alpha emissions from the hydrogen exosphere of Mars. The model is currently being used to study seasonal changes from the hydrogen exosphere of Earth. The same model will be used to simulate the Lyman alpha emissions from the neutral H exosphere of Uranus. Dr. Bhattacharyya is also extremely familiar with the ACS and STIS instrument onboard HST and has been involved in multiple successful HST observing campaigns (3 as PI and 4 as Co-I) in the past. Dr. Bhattacharyya has also authored multiple papers on RT simulations of the martian exosphere using HST observations as well as led the HST calibration campaign to calibrate the ACS detector at Lyman alpha using the STIS instrument (GO-15098). Co-I John Clarke is an expert with all aspects of the Hubble Space Telescope and was HST project scientst and instrument scientist from 1984-1987. Prof. Clarke will advise on the instrumental aspects as well as the data reduction procedures for the archival data to be used in this study. Co-I Henrik Melin is an expert on deriving temperatures of the uranian thermosphere from H3+ emissions and has authored numerous publications on the same. Dr. Melin will advise on the characteristics of the temperature structure of the background atmosphere during the modeling process, required for this study. Co-I Luke More is an expert on giant planet upper atmospheres and thermospheres has numerous authored several publications on giant planet ionospheres, using H3+ emissions to charactrize their temperatures, and ring particle drag in Jupiter and Saturn's exospheres. Dr. Moore will assist with determing the background atmospheric characteristics like density distribution of CH4 at Uranus as well as help interpret the exospheric density results in terms of Uranus' ring particle drag effects as well as effects on satellite missions. Co-I Jean-Yves Chaufray is an expert on radiative transfer theory and has numerous publications on the same. Dr. Chaufray will advise on the radiative transfer modeling aspects, especially with regards to energetic H simulations in the RT model for Uranus. Solar System Astronomy 0 Regular false false true false false SUPPORTED