Venus transit 2004: Illustrating the capability of exoplanet transmission spectroscopy

P. Hedelt^1,2, R. Alonso³, T. Brown⁴, M. Collados Vera⁵, H. Rauer^6,7, H. Schleicher⁸, W. Schmidt⁸, F. Schreier⁹ and R. Titz⁶

¹ CNRS, UMR 5804, Laboratoire d’Astrophysique de Bordeaux, 2 rue de l’Observatoire, BP 89, 33271 Floirac Cedex, France
e-mail: pascal.hedelt@obs.u-bordeaux1.fr
² Université de Bordeaux, Observatoire Aquitain des Sciences de l’Univers, 2 rue de l’Observatoire, BP 89, 33271 Floirac Cedex, France
³ Observatoire Astronomique de l’Université de Genève, 51 chemin des Maillettes, 1290 Sauverny, Switzerland
⁴ Las Cumbres Observatory Global Telescope, 6720 Cortona Dr. Ste. 102, Goleta, CA 93117, USA
⁵ Instituto de Astrofisica de Canarias, 38200 La Laguna, Tenerife, Spain
⁶ Institut für Planetenforschung, Deutsches Zentrum für Luft- und Raumfahrt, Rutherfordstr. 2, 12489 Berlin, Germany
⁷ Zentrum für Astronomie und Astrophysik, Technische Universität Berlin, Hardenbergstr. 36, 10623 Berlin, Germany
⁸ Kiepenheuer-Institut für Sonnenphysik, Schöneckstr. 6, 79104 Freiburg, Germany
⁹ Institut für Methodik der Fernerkundung, Deutsches Zentrum für Luft- und Raumfahrt, 82234 Oberpfaffenhofen-Wessling, Germany

Received: 30 November 2010
Accepted: 1 August 2011

Abstract

The transit of Venus in 2004 offered the rare possibility to remotely sense a well-known planetary atmosphere using ground-based absorption spectroscopy. Transmission spectra of Venus’ atmosphere were obtained in the near infrared using the Vacuum Tower Telescope (VTT) in Tenerife. Since the instrument was designed to measure the very bright photosphere of the Sun, extracting Venus’ atmosphere was challenging. We were able to identify CO₂ absorption lines in the upper Venus atmosphere. Moreover, the relative abundance of the three most abundant CO₂ isotopologues could be determined. The observations resolved Venus’ limb, showing Doppler-shifted absorption lines that are probably caused by high-altitude winds. We demonstrate the utility of ground-based measurements in analyzing the atmospheric constituents of a terrestrial planet atmosphere using methods that might be applied in future to terrestrial extrasolar planets.