1. LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, 5 place Jules Janssen, 92195 Meudon, France
2. INAF-IASF,
3. INAF-IFSI, 100 Via del Fosso del Cavaliere, 00133 Rome, Italy
4. LPAP-Université de Liège, 5 Avenue de Cointe, B-4000 Liège, Belgium
5. Instituto de Astrofisica de Andalucia (CSIC), 50 Camino Bajo de Huetor, 18008 Granada, Spain
6. Universidad del Pais Vasco, Escuela Superior de Ingenieros, Física Aplicada I, C/Alda. Urquijo s/n 48013, Bilbao, Spain
7. Space Research Institute (IKI), Profsouznaya 84/32, Moscow, Russia
8. Atmospheric, Oceanic and Planetary Physics, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
9. CISAS Università di Padova, 1 via Venezia, I-35131 Padova, Italy
10. German Aerospace Center (DLR), 2 Rutherfordstrae, 12489 Berlin-Adlershof, Germany
11. Jet Propulsion Laboratory, 4800 Oak Grove Drive, Pasadena, California 91109, USA
12. Institut d'Astrophysique Spatiale, batiment 121, Université de Paris-Sud, 91405 Orsay, France
13. Dipartimento di Fisica, Università degli Studi di Lecce, Via Arnesano, 73100 Lecce, Italy
14. Centrum Badan Kosmicznych Pan (CBK), 00716 Warszawa, Bartycka 18A, Poland
15. AMDLSPACE, 33 Via Giovanni Angelini, 00149 Rome, Italy
16. Dynamique Terrestre et Planétaire, CNRS UMR5562, Observatoire Midi Pyrénées, 31400 Toulouse, France
17. Laboratoire de Météeorologie Dynamique, UPMC, 4 place Jussieu, 75252 Paris cedex 05, France
18. Universita d'Annunzio, 42 Viale Pindaro, 65127 Pescara, Italy
19. Lisbon Astronomical Observatory, Tapada da Ajuda, 1349-018 Lisbon, Portugal
20. Politecnico di Milano, 26 Piazza Leonardo Da Vinci, 20133 Milano, Italy
21. University of Amsterdam, 403 Kruislaan, 1098 SJ Amsterdam, The Netherlands
22. Max-Planck Institute for Aeronomy, 2 Max-Planck-Strasse, 37191 Katlenburg-Lindau, Germany
23. University of l'Aquila, Dipartimento di Fisica, 10 Via Vetoio, 67010 Coppito l'Aquila, Italy
24. INAF-IFSI, 00133 Rome, Italy.
25. Galileo Avionica, Florence, 50013, Italy.
26. DLR, 12489 Berlin, Germany.
27. Università di Padova, 35131, Italy.
28. INAF-IASF, 00133 Rome, Italy.
29. IAS Orsay, 91405, France.
30. LESIA, Observatoire de Paris, France.
31. ASI Rome, 00198, Italy.
32. Techno System Developments, Naples, 80078, Italy.
33. Kayser Threde, Munich, 81379, Germany.

Correspondence to: P. Drossart¹ Correspondence and requests for materials should be addressed to P.D. (Email: pierre.drossart@obspm.fr).

Abstract

The upper atmosphere of a planet is a transition region in which energy is transferred between the deeper atmosphere and outer space. Molecular emissions from the upper atmosphere (90–120 km altitude) of Venus can be used to investigate the energetics and to trace the circulation of this hitherto little-studied region. Previous spacecraft¹ and ground-based^{2, 3, 4} observations of infrared emission from CO₂, O₂ and NO have established that photochemical and dynamic activity controls the structure of the upper atmosphere of Venus. These data, however, have left unresolved the precise altitude of the emission¹ owing to a lack of data and of an adequate observing geometry^{5, 6}. Here we report measurements of day-side CO₂ non-local thermodynamic equilibrium emission at 4.3 m, extending from 90 to 120 km altitude, and of night-side O₂ emission extending from 95 to 100 km. The CO₂ emission peak occurs at 115 km and varies with solar zenith angle over a range of 10 km. This confirms previous modelling⁷, and permits the beginning of a systematic study of the variability of the emission. The O₂ peak emission happens at 96 km  1 km, which is consistent with three-body recombination of oxygen atoms transported from the day side by a global thermospheric sub-solar to anti-solar circulation, as previously predicted⁸.

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