Jupiter's violent moon Io has been the solar system's most volcanic body for around 4.5 billion years 

 Jupiter's moon Io is the solar system's most volcanic body thanks to a gravitational tug of war that rages below its surface. But now scientists know the violent moon has always been this way.  

https://cdn.mos.cms.futurecdn.net/HKng7LBhMJmci3okenfojH.jpg

https://www.space.com/jupiter-moon-io-most-volcanic-body-solar-system-4-5-billion-years