Overview
- A team led by Julia V. Seidel reports in Nature Astronomy that measurements of seven tidally locked ultra-hot Jupiters show a clear trend of slower winds on hotter planets, a finding published on Tuesday that the authors say is best explained by magnetic braking of ionized atmospheres.
- Researchers used high-resolution spectrographs (ESPRESSO on ESO’s VLT and MAROON-X on Gemini North) to track Doppler shifts of atmospheric absorbers such as iron and derived wind speeds ranging from about 7,200 km/h to more than 25,000 km/h.
- The team infers planet-wide magnetic fields because charged particles in the very hot, partly ionized atmospheres would be slowed by a global magnetic field, a mechanism known as magnetic braking that converts wind momentum into electromagnetic effects.
- From the wind data the authors estimate magnetic strengths roughly comparable to Solar System planets — about four times Saturn’s up to about half of Jupiter’s — an inference that helps explain why radio searches have so far found weak or no strong exoplanet radio signals.
- Next steps include targeted follow-up surveys to observe cooler gas giants and attempts to detect more direct magnetic signatures with current facilities and upcoming telescopes such as the Extremely Large Telescope, ARIEL, and the Giant Magellan Telescope.