A rocky extrasolar moon (exomoon) with bubbling lava may orbit a planet 550 light-years away from us. This is suggested by an international team of researchers led by the University of Bern on the basis of theoretical predictions matching observations. The “exo-Io” would appear to be an extreme version of Jupiter’s moon Io.
Source:
https://phys.org/news/2019-08-hints-volcanically-exomoon.html