Free Astronomy Magazine November-December 2017

54 NOVEMBER-DECEMBER 2017 SPACE CHRONICLES A s WASP-19b passes in front of its parent star, some of the starlight passes through the planet’s atmosphere and leaves subtle fingerprints in the light that eventually reaches Earth. By using the FORS2 instrument on the Very Large Telescope the team was able to carefully analyse this light and deduce that the atmosphere contained small amounts of titanium oxide, water and traces of sodium, alongside a strongly scattering global haze. [ESO/M. Kornmesser] heat from entering or escaping through the atmosphere, leading to a thermal inversion — the tempera- ture is higher in the upper atmo- sphere and lower further down, the opposite of the normal situation. Ozone plays a similar role in Earth’s atmosphere, where it causes inver- sion in the stratosphere. “The presence of titanium oxide in the atmosphere of WASP-19b can have substantial effects on the at- mospheric temperature structure and circulation.” explains Ryan Mac- Donald, another team member and an astronomer at Cambridge Univer- sity, United Kingdom. “To be able to examine exoplanets at this level of detail is promising and very excit- ing.” adds Nikku Madhusudhan from Cambridge University who oversaw the theoretical interpreta- tion of the observations. The astronomers collected observa- tions of WASP-19b over a period of more than one year. By measuring the relative variations in the planet’s radius at different wavelengths of light that passed through the exo- planet’s atmosphere and comparing the observations to atmospheric models, they could extrapolate dif- ferent properties, such as the chem- ical content, of the exoplanet’s at- mosphere. This new information about the presence of metal oxides like tita- nium oxide and other substances will allow much better modeling of exoplanet atmospheres. Looking to the future, once astronomers are able to observe atmospheres of pos- sibly habitable planets, the im- proved models will give them a much better idea of how to inter- pret those observations. “This important discovery is the out- come of a refurbishment of the FORS2 instrument that was done ex- actly for this purpose,” adds team member Henri Boffin, from ESO, who led the refurbishment project. “Since then, FORS2 has become the best instrument to perform this kind of study from the ground.” !