Interpreting the velocity profile of exoplanet atmospheres

With instruments like CRIRES+ on ESO’s VLT, astronomers can track the speed of molecules in exoplanet atmospheres. This animation shows the method used to infer the velocity of winds on distant exoplanets, like the giant gas planet WASP-127b, located about 520 light-years from Earth.

When the planet crosses between its host star and us, the light of the star goes through the planet’s atmosphere, where different molecules absorb specific colours or wavelengths. If these molecules are moving, these absorbed colours will be shifted towards bluer wavelengths if the molecules are moving towards us, and redder ones if they are moving away.

The spectrum of WASP-127b shows a double peak, meaning that part of the atmosphere is moving towards us while the other part is moving away from us. In other words: there is wind circling around the planet. The larger the wavelength separation between the peaks in the spectrum, the faster the wind, which in the case of WASP-127b moves at an impressive 9 km per second.

A more detailed analysis of the shape of these lines allowed astronomers to infer that this fast wind is actually constrained to the planet’s equator –– a jet stream.