Astronomers have spotted a plume of sodium near a distant planet. The gas is so far from the surface that they say it must have come from a volcanic exomoon
Source:
https://www.newscientist.com/article/2214859-we-may-have-seen-signs-of-an-exomoon-spewing-out-volcanic-gas/?utm_campaign=RSS%7CNSNS&utm_source=NSNS&utm_medium=RSS&utm_content=home