Atmospheric evolution and the search for species of astrobiological interest in the Solar System – Case Studies using the Planetary Spectrum Generator

We used the Planetary Spectrum Generator (PSG) [1] a radiative transfer suite, with the goal of simulating spectra from observations of Venus, Mars and Jupiter, searching for minor chemical species.

For Venus, sulphur dioxide (SO₂) absorption lines were detected and its abundance constrained, by comparing simulations with observations by the Texas Echelon Cross Echelle Spectrograph (TEXES) spectrograph, around 7.4 μm [2]. The mean abundance of SO₂ was constrained to 120 ppb, using the Optimal Estimation Method [3] and a line-depth ratio method [2] independently, in agreement with 50-175 ppb obtained by Encrenaz et al [2].  Phosphine (PH3) was not detected in the comparison between simulation and TEXES Infrared (IR) observations [4], around 10.5 μm, due to the presence of a strong telluric water band in the spectra.

For Mars, both a positive and a negative detection of methane were reanalyzed using PSG simulations with the goal of constraining the methane abundance. The related spectra observations in the IR, around 3.3 μm, report, respectively, to the Mars Express (MEx) [5] and ExoMars [6] space-probes.

For Jupiter, the detection of ammonia, phosphine, deuterated methane and methane was studied, by comparing simulations with IR observations by the Infrared Space Observatory (ISO), around 7-12 μm. [7]. The next step is focused in the determination of the abundances of the previous species. Independent simulations will be performed using PSG and the NEMESIS state-of-the-art radiative transfer suite [8]

Funding: This research was funded by the Portuguese Fundacao Para a Ciencia e Tecnologia under project P-TUGA Ref. PTDC/FIS-AST/29942/2017 through national funds and by FEDER through COMPETE 2020 (Ref. POCI-01-0145 FEDER-007672).

Aknowledgments: We credit Thérèse Encrenaz, from LESIA, Observatoire de Paris, for all the support and fruitful discussion; Geronimo Villanueva, from NASA-Goddard Space Flight Center, for discussing issues regarding PSG; Marco Giuranna, PI of the PFS instrument of Mars Express (ESA), Alejandro Cardesín, from ESAC-ESA, Ann Carine Vandaele, PI of the NOMAD instrument of ExoMars (ESA) and Séverine Robert, from the ExoMars team, for all the support regarding Mars dedicated research; Gabriella Gilli (IAA), for the collaboration regarding the LMD-VGCM model; Patrick Irwin, from the University of Oxford (UK), for the collaboration under the NEMESIS radiative transfer code; Asier Munguira, from the University of the Basque Country, for his availability to discuss atmospheric research methods in the context of the present work.

References

[1] Villanueva et al. 2018, Journal of Quantitative Spectroscopy and Radiative Transfer

[2] Encrenaz et al. 2012; Astronomy & Astrophysics

[3] C. D. Rodgers. Inverse methods for atmospheric sounding: theory and practice. World Scientific, 2008

[4] Encrenaz et al. 2020; Astronomy & Astrophysics.

[5] Giuranna et al. 2019; Nature

[6] Korablev et al. 2019.; Nature

[7] Encrenaz et al. 1999 ; Planetary and Space Science

[8] Irwin et al. 2008 ; Journal Of Quantitative Spectroscopy And Radiative Transfer