APOD: 2022 August 13 - Herschel Crater on Mimas

Good evening, Rallypoint, and welcome to the August 13th edition of Astronomy Picture of the Day ("APOD): "Herschel Crater on Mimas." Mimas was discovered William Herschel September 17, 1789. His notes on the discovery speak of the "seventh satellite" of Saturn. We didn't get a close up view of Mimas until Cassini (2010) flew by at a distance of 9500 miles. Suffice it to say the imagery was eye-opening.

The large impact crater we see in today's APOD is called Herschel Crater. Its diameter 81 miles (the diameter of Mimas is 246 miles). A crater of an equivalent scale on Earth (in relative size) it would be wider than Australia (2,500 mi in diameter). If it was any larger, the impact would have potentially shattered Mimas.

So what is it about Mimas that allowed it to take such a punch? Using data gathered by Cassini, scientists at the Southwest Research Institute developed a tidal heating model for Mimas that suggested an internal ocean concealed by a stable icy shell between 14-20 miles in thickness. This model matched the visual and orbital data gathered by Cassini. And there is already evidence that suggests an internal ocean on the Saturnian moons Europa and Enceladus.

I'll post the photos from Cassini that show plumes of water ice from Enceladus in a separate comment. Could Mimas be another similar world?