Io-like volcanic moon may have been discovered orbiting exoplanet WASP-4b - YouTube - Space.com - planetary science

Scientists believe they may have discovered a volcanic exomoon orbiting the exoplanet WASP-4b 635 light years from Earth (right next door).The discovery was made at the European Southern Observatory's 3.6 m/11.81 ft telescope at La Silla,Chile.A large cloud of sodium gas,typical of volcanic eruptions,was observed near the exoplanet.Although we lack the technology to observe exomoons directly,their existance can be ascertained by deduction.*Credits:NASA/Jet Propulsion Laboratory-California Institute of Technology