... Europa's ocean sits under a thick ice shell. If this ocean covers the moon's solid core, does the shell rotate at a different speed? ... To the best of our knowledge, Europa has an ice shell of a few to as many as 12 miles (20 kilometers) in thickness, underneath which lies a global 60-mile-deep (100km) liquid water ocean. ... Get instant access to subscriber content on Astronomy.com! ... If you are already registered on Astronomy.com, please log in below. ...