Venus transit 2004: Illustrating the capability of exoplanet transmission spectroscopy

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 groundbased measurements in analyzing the atmospheric constituents of a terrestrial planet atmosphere using methods that might be applied in future to terrestrial extrasolar planets

Remote Sensing of Venus' atmosphere during the June 2004 transit

Using data from the Venus-Sun transit on 8th of June 2004, one can make estimates about the feasability of making positive spectral detections of biomarkers in extrasolar planet atmospheres. During the transit, transmission spectra from venusian atmospheric layers were measured in three wavelength regions in the near-infrared. Absorption lines of the most abundant molecule CO2 and its isotopes were detected. The line-by-line, high-resolution radiative transfer program SQuIRRL (Schwarzschild Quadrature Infrared Radiation Line-by-line) was used to calculate and validate the observed absorption line