How to lose a thousand tons of atmosphere per second

Astronomers using the NASA/ESA Hubble Space Telescope have seen dramatic changes in the upper atmosphere of a faraway planet. Just after a violent flare on its parent star bathed it in intense X-ray radiation, the planet’s atmosphere gave off a powerful burst of evaporation. The observations give a tantalising glimpse of the changing climates and weather on planets outside our Solar System.

This artist’s impression shows exoplanet HD 189733b, as it passes in front of its parent star, called HD 189733A. Hubble’s instruments observed the system in 2010, and in 2011 following a large flare from the star (depicted in the image). Following the flare, Hubble observed the planet’s atmosphere evaporating at a rate of over 1000 tonnes per second. In this picture, the surface of the star, which is around 80% the mass of the Sun, is based on observations of the Sun from the Solar Dynamics Observatory. Credit: NASA, ESA, L. Calçada

Tau Boötis b, a six Jupiter-mass planet orbiting very close to its parent star

For the first time a clever new technique has allowed astronomers to study the atmosphere of an exoplanet in detail — even though it does not pass in front of its parent star. An international team has used ESO’s Very Large Telescope to directly catch the faint glow from the planet Tau Boötis b. They have studied the planet’s atmosphere and measured its orbit and mass precisely for the first time — in the process solving a 15-year old problem. Surprisingly, the team also finds that the planet’s atmosphere seems to be cooler higher up, the opposite of what was expected. The results were published in the 28 June 2012 issue of the journal Nature.

This artist’s impression shows the exoplanet Tau Boötis b. This was one of the first exoplanets to be discovered back in 1996, and it is still one of the closest planetary systems known to date. Astronomers using ESO’s Very Large Telescope have now caught and studied the faint light from the planet Tau Boötis b for the first time. By employing a clever observational trick the team find that the planet’s atmosphere seems to be cooler higher up, the opposite of what was expected. Credit: ESO/L. Calçada