The exoplanet named HD 189733b, a gas-giant located 63 light-years away from Earth in the constellation Vulpecula (the "little fox"), is several thousand degrees hot. The temperature increases with altitude and reaches more than 3,000 degrees Celsius, enough to melt iron. "This is a sign that heating takes place at high altitudes in the planetary atmosphere," said Aurélien Wyttenbach, a Ph.D. student at Geneva Observatory, according to a press release. Besides deriving a temperature profile of the planetary atmosphere, the Geneva team found evidence of high-altitude winds blowing from the exoplanet's hot day-side to the cold night-side with speeds of several kilometers per second - "also an unprecedented detection," added Wyttenbach.

The results, based on observations with ESO's ground-based telescope mounted by the HARPS spectrograph in Chile, are supported by a theoretical study by Kevin Heng, a professor and astrophysicist at the University of Bern. These two studies are the result of collaboration between the Universities of Geneva and Bern for planetary and exoplanetary science known as "PlanetS."

"Previous formulae assumed the atmosphere to have only a single temperature, but we know that this is probably too simplistic even for faraway exoplanets for which we have limited information," said Kevin Heng, according to the press release. "Our motivation was to derive new and simple formulae that took into account the changing temperatures and were specifically designed to interpret sodium lines. Their simplicity allow the formulae to be easily applied, so that one may obtain a quick and relatively robust answer without crunching numbers in a computer. Sometimes, simple is better."

According to the press release, with the next generation of instruments and telescopes coming online in the next decade, the observational and theoretical techniques discovered by these two studies will be useful to other astronomers around the world seeking to explore and study the atmospheres of other exoplanets.

* Wyttenbach, A., Ehrenreich, D., Lovis, C., Udry, S. & Pepe, F.: Spectrally resolved detection of sodium in the atmosphere of HD189733b with the HARPS spectrograph, 2015, Astronomy & Astrophysics, DOI:

* Heng, K., Wyttenbach, A., Lavie, B., Sing, D.K., Ehrenreich, D., & Lovis, C.: A non-isothermal Theory for Interpreting Sodium Lines in Transmission Spectra of Exoplanets, 2015, Astrophysical Journal Letters, DOI:

The National Center of Competence in Research (NCCR) PlanetS is a collaboration between the Universities of Bern, Geneva and Zurich, ETH Zurich and EPF Lausanne. It was established by the Swiss National Science Foundation in June 2014 and studies the origin, evolution and characterization of planets.