Close‑in planet’s magnetic bond lights up its star’s chromosphere
Astronomers studying the nearby red dwarf GJ 436 and its 2.6‑day, roughly four‑Earth‑mass planet found periodic brightenings in the star’s chromosphere that align with the planet’s orbit, likely caused by magnetic fields linking the two bodies. A model that also factors in the star’s rotation and surface activity explains a slight lag between the signal and the orbit. The study suggests the planet has a magnetic field of at least 6 gauss (around 10× Earth’s, similar to Jupiter’s), indicating that magnetic star–planet interactions may be a common way to probe exoplanet magnetism across close‑in systems.