Preliminary results on spectral line survey of Uranus at the millimeter/sub-millimeter wavelength using ALMA data

Abstract

Abstract Previous studies and spectroscopy observations concluded that Uranus has the fewest spectral line features among other giant planets. It is challenging yet very possible to conduct the line survey with the abundance of available Uranus observation data, particularly in millimeter/sub-millimeter. As a sensitive radio interferometer, Atacama Large Millimeter/submillimeter Array (ALMA) frequently observes Uranus from wide viewing windows and the narrow spectral resolution which is very suitable for spectral survey study. In this paper, we report the preliminary results of Uranus’ spectral line survey over various ranges of ALMA spectral windows at bands 3 to 9, taken from 2012 – 2018. With CASA data processing tools, the survey results from 451 spectral windows (spw), 216 line candidates from 98 spw were suspected as the first step to examine molecule’s existence in Uranus. Although most of them had SNR below 3, some prominent spectral line features were detected tentatively such as the line profiles at the frequency of carbon monoxide (CO) and methanol (CH3OH). The inconsistent results on CO confirmed the previous theory that this molecule might be originally from external. Although this CO detection is an important finding as it might be the first time to be discovered in Uranus from ALMA, to declare as a real detection, it is necessary to confirm with more observations and correction with some relevant factors.