Airglow Emissions in the Terrestrial Atmospheres. A. Migliorini1, G

Comparative Climatology of Terrestrial Planets (2012) 8006.pdf

Airglow emissions in the terrestrial atmospheres. A. Migliorini1, G. Piccioni1, F. Capaccioni1, G. Filacchione1, F. Tosi1, R. Politi1, P. Drossart2, 1IAPS (via del Fosso del Cavaliere, 100, 00133 Roma, Italy), 2LESIA (5, Place J. Jansen, 92150 Meudon, Paris).

Introduction: The Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) is one of the instru- ments on board the European mission to Venus, Venus Express [1, 2]. It allows the investigation of the airglow emissions both in the visible and IR ranges [3]. The simultaneous observations of the O2 emissions at 1.27 µm and 1.58 µm [3], the detection of the O2 Herzberg II and the Chamberlain systems in the visible Figure 2. Vertical profile of the (0-0) and the (0-1) range [4, 5], as well as the first detection of the OH O2 bands, centred at 1.27 µm and 1.58 µm respective- emissions [6] are some of the issues obtained with the ly, observed by VIRTIS/Venus Express. VIRTIS instrument. VIRTIS/Venus Express is the twin instrument of VIRTIS on board the Rosetta S/C In addition, the OH emissions in the IR were de- [7]. Along its route to the comet 67P/Churyumov– tected for the first time in the Venus atmosphere [6]. Gerasimenko, the Rosetta S/C performed three flybys OH maximum emission is in agreement with the O2 with the Earth and Mars. VIRTIS/Rosetta provided the peak position, though the former is less subject to the unique opportunity to investigate the airglow emis- dynamical circulation from day to night, driven by the sions on Mars and the Earth, which can be then com- temperature gradient between the two hemispheres. pared to the results obtained with VIRTIS/Venus Ex- press for the Venus atmosphere. However, it must be Comparison with the terrestrial planets: The ob- recalled that the airglow emissions in the Venus case servations of the Earth and Mars atmospheres with are mainly driven by dynamics, while in the Earth case VIRTIS/Rosetta allow to analyse the oxygen emissions they are subjected to chemistry. for these planets and investigate physical processes occurring in their atmospheres. Results: The most prominent emissions observed The peak position of the (0-0) O2 band at limb is at in the nightside of Venus are the O2 (0-0) and (0-1) about 70 km height in the case of the Earth nightglow, Atmospheric bands at 1.27 µm and 1.58 µm, and the in agreement with previous observations [8]. Indica- OH transitions with Δν = 1, 2, centred at 2.81 µm and tions of the presence of the (0-0) O2 nightglow emis- 1.46 µm, respectively. An example of the sion in the Mars atmosphere has been found in the VIRTIS/Venus Express nightside spectrum is shown in VIRTIS/Rosetta data. The intensity of the (0-0) O2 figure 1, obtained by averaging about 700 spectra se- band is very weak, but in agreement with the CRISM lected in the altitude range 90-100 km. observations [9]. Despite some spurious features in the VIRTIS/Rosetta spectrum of the Earth atmosphere, we are able to derive the profile for the OH transitions with Δν = 1, at 2.81 µm. The OH emission in the Earth atmosphere peaks at about the same altitude as the O2 (0-0) band, as it is found in the venusian case [6]. The oxygen dayglow emission is observed for Mars and the Earth. The maximum of emission is set at Figure 1. Spectrum of the Venus atmospheres, ac- about 40 km height for the Earth. Some trend of air- quired with VIRTIS/Venus Express. glow intensity with respect to local time can also be investigated in the case of Mars and the Earth due to The O2 emissions at 1.27 µm and 1.58 µm, refered the full disk observations during the Rosetta flybys 1 as the (0-0) and the (0-1) emission bands of the (a Δg – with the planets. 3 - X Σ g), in the Venus atmosphere show a maximum at 97.4 ±2.5 km (figure 2) [3]. The (0-1) band is found to References: be 63 times less intense than the (0-0) O2 band [3]. [1] Piccioni et al., in press, ESA-SP 1295. [2] Drossart et al., (2007) P&SS, 45. [3] Piccioni et al., Comparative Climatology of Terrestrial Planets (2012) 8006.pdf

(2009), JGR, 114. [4] Garcia-Munoz et al., (2009) JGR, 114. [5] Migliorini et al., (2012) EGU meeting. [6] Piccioni et al., (2008) A&A, 483. [7] Coradini et al., (2007), Space Science Reviews, 128. [8] Tarasick and Evans, (1993) Adv. Space Res., 13. [9] Clancy et al., (2011) EPSC-DPS Joint Meeting 2011.

Acknowledgment: The authors acknowledge ESA, ASI and all the european national agencies supporting Venus Express and Rosetta missions. This research is funded thanks to ASI grants (ASI-INAF I/050/10/0, ASI-INAF I/062/08/0).