Hints of volcanic moon around alien planet may be 1st-of-its-kind discovery (video) 

 A sodium cloud detected in the vicinity of an exoplanet named WASP-49 b hints at the presence of a natural satellite, also known as an exomoon. 

https://cdn.mos.cms.futurecdn.net/ycJvyjwxxFe9aHKSMUQGE.jpg

https://www.space.com/possible-volcanic-exomoon-jupiter-moon-io