Io's SO2 atmosphere from HST Lyman-α images: 1997 to 2018

• DOI: 10.1016/j.icarus.2020.114212
• Publication Date: 2020-11-17T01:48:58Z
• Authors: Gabriel Giono; Lorenz Roth
• Keywords: 13. Climate action; 01 natural sciences; 7. Clean energy; 0105 earth and related environmental sciences

The atmosphere of Jupiter's volcanic moon Io consists mainly sulfur dioxide (SO2), and this main constituent has been studied with a variety observing techniques across many wavelengths over the years. Here we study absorption by SO2 at hydrogen Ly-α line (1216 Å) in large set images taken Space Telescope Imaging Spectrograph (STIS) onboard Hubble (HST) between 1997 2018. An advanced statistical analysis using Monte-Carlo trial method is applied to derive column density from intensity, which includes uncertainties used variables such as solar background flux. Our produces probability distribution function highlights some short-comings technique. Most importantly, HST/STIS surface-reflected flux are only sensitive densities ~1015 cm−2 ~5×1016 cm−2. Due strong non-linearity relationship abundance low high values detected flux, directly retrieved STIS will generally fall within these boundaries. This explains relatively equatorial about 1016 reported previous studies (e.g., Feldman et al., 2000; Feaga 2009) compared other Spencer 2005; Tsang 2013; Jessup Spencer, 2015; Lellouch 2015), where obtained often 1017 By assuming log-normal for density, new estimate then fitted, indirectly accounting abundances beyond detectability limits. suggests slightly higher much larger upper-limits, revealing that observations fact consistent found studies. We investigate three sites (Loki, Marduk, Thor), plumes were observed before sensitivity our comparably high. did not reveal transient changes due local outgassing any sites. Finally, heliocentric distance changed 4.95 AU 5.45 observation dates, potentially allowing us influence intensity on via surface frost sublimation. However, derived error bars significantly than variability, preventing firm conclusion seasonal outgassing.