1. INAF-IASF (Istituto di Astrofisica Spaziale e Fisica Cosmica),
2. CNR-ISAC (Istituto di Scienze dell'Atmosfera e del Clima),
3. INAF-IFSI (Istituto di Fisica dello Spazio Interplanetario), via del fosso del Cavaliere 100, 00133 Rome, Italy
4. LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, 5 place Jules Janssen, 92195 Meudon, France
5. Departamento de Física Aplicada I, Escuela Superior de Ingenieros Universidad del Pais Vasco Alda, Urquijo s/n 48013, Bilbao, Spain
6. Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, UK
7. Space Research Institute of Russian Academy of Sciences (IKI), Profsojuznaja 84/32, 117997 Moscow, Russia
8. Laboratoire de Meteorologie Dynamique, Jussieu, Box 99, 75252 Paris cedex 05, France
9. CISAS Università di Padova, via Venezia 1, 35131 Padova, Italy
10. German Aerospace Center (DLR), Institute of Planetary Exploration, Planetary Physics Section, Berlin-Adlershof Rutherfordstrasse 2, 12489 Berlin, Germany
11. Jet Propulsion Laboratory, MS 183-601, Pasadena, California 91011, USA
12. Institut d'Astrophysique Spatiale, Bâtiment 120, Université Paris-Sud, 91405 Orsay Cedex, France
13. Università degli Studi di Lecce, Dipartimento di Fisica, Via Arnesano, 73100 Lecce, Italy
14. Space Research Centre of Polish Academy of Science, Bartycka 18A, 00-716 Warszawa, Poland
15. AMDLSPACE s.r.l., Via Giovanni Angelini 33, 00149 Rome, Italy
16. Département des E´tudes Spatiales, Institut de Physique du Globe de Paris 4, Avenue de Neptune, F-94107 Saint Maur des Fossés cedex, France
17. Instituto de Astrofísica de Andalucía (CSIC), Camino Bajo de Huétor, 24 Apartado 3004, 18080 Granada, Spain
18. International Research School of Planetary Sciences, Dipartimento di Scienze, Universita' d'Annunzio, Viale Pindaro 42, 65127 Pescara, Italy
19. Observatorio Astronomico de Lisboa, Centro de Astronomia e Astrofisica da Universidade de Lisboa, Tapada da Ajuda 1349-018, Lisboa, Portugal
20. Politecnico di Milano, Polo di Lecco, Via Marco D'Oggiono 18/A, 23900 Lecco, Italy
21. Astronomical Institute "Anton Pannekoek", University of Amsterdam, Kruislaan 403, 1098 SJ, Amsterdam, The Netherlands
22. Max Planck Institute for Aeronomy, Max Planck Str. 2, 37191 Katlenburg-Lindau, Germany
23. Dipartimento di Fisica, Università de L'Aquila, via Vetoio Loc. Coppito, 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. IAS Orsay, 91405, France.
29. LESIA, Obs. de Paris, 92195 Meudon, France.
30. INAF-IASF, 00133 Rome, Italy.
31. ASI, Rome, 00198, Italy.
32. Techno System Developments, Naples, 80078, Italy.
33. Kayser Threde, Munich, 81379, Germany.

Correspondence to: G. Piccioni¹ Correspondence and requests for materials should be addressed to G.P. (Email: Giuseppe.piccioni@iasf-roma.inaf.it).

Abstract

Venus has no seasons, slow rotation and a very massive atmosphere, which is mainly carbon dioxide with clouds primarily of sulphuric acid droplets. Infrared observations by previous missions to Venus revealed a bright 'dipole' feature surrounded by a cold 'collar' at its north pole^{1, 2, 3, 4}. The polar dipole is a 'double-eye' feature at the centre of a vast vortex that rotates around the pole, and is possibly associated with rapid downwelling. The polar cold collar is a wide, shallow river of cold air that circulates around the polar vortex. One outstanding question has been whether the global circulation was symmetric, such that a dipole feature existed at the south pole. Here we report observations of Venus' south-polar region, where we have seen clouds with morphology much like those around the north pole, but rotating somewhat faster than the northern dipole. The vortex may extend down to the lower cloud layers that lie at about 50 km height and perhaps deeper. The spectroscopic properties of the clouds around the south pole are compatible with a sulphuric acid composition.

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