Mimas
What is Mimas?
Moons· Diameter 396 km. Saturn's small inner moon, a dead ringer for the Death Star thanks to its huge Herschel crater. It is the smallest body known to be rounded by its own gravity, and in 2024 it surprised everyone with a young ocean beneath its ice. Watch its fast orbit just outside the rings in the orbit view.
📍 Visible from where you are right now — computed in your browser
bearing · altitude · rise time · best time tonight
The orbit of Mimas at this moment: https://nowsky.org/solar/orbit?fw=moon:saturn:mimas&sp=0.004 — replayed live, no login.
Orbit and size
| Diameter | 396 km |
|---|---|
| Distance from Saturn | 185,500 km |
| Orbit | 22.6 h |
| Note | 130-km Herschel crater; subsurface ocean found in 2024 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Parent planet and sibling moons
Frequently asked
- How big is Mimas?
- 396 km.
- How far is Mimas from Earth?
- 185,500 km.
- What is notable about Mimas?
- 130-km Herschel crater; subsurface ocean found in 2024.
- Which planet does Mimas orbit?
- Saturn.
The moon that carved a gap in the rings
The Cassini Division, the 4,800 km gap that splits Saturn's rings into A and B, is Mimas's doing. Ice particles at the gap's inner edge sit in a 2:1 resonance with Mimas — two orbits for each of its one — and being tugged at the same point again and again, their orbits were disturbed until they were swept away. A moon 396 km across cut a dark line through rings 280,000 km wide.
Mimas leaves other marks across the rings. The outer edge of the B ring is not a circle but a two-lobed shape because of the same 2:1 resonance, and several wave patterns in the A ring sit at other Mimas resonances. The young ocean found inside Mimas in 2024 (formed within the last 25 million years) fits the reading that the resonance reached its present state only recently, adding to the case that Saturn's rings and moon system are younger than once thought.
The moon in depth
Mimas was discovered by William Herschel in 1789. At 396 km across it orbits just outside Saturn's rings, 185,500 km out, every 22.6 hours. It is the smallest known body rounded by its own gravity, and it is the sculptor of the Cassini Division: particles there orbit in 2:1 resonance with Mimas and are swept clear.
Its signature feature is Herschel crater, 130 km wide — a third of the moon's diameter — which gives Mimas its famous resemblance to the Death Star from Star Wars. Calculations suggest a slightly harder impact would have shattered the moon entirely. Long dismissed as a frozen, inert world, Mimas stunned scientists in 2024 when a re-analysis of Cassini data revealed a young ocean, less than 25 million years old, beneath 20–30 km of ice.
Track Saturn in the orbit view and zoom in to catch Mimas hugging the edge of the rings on its fast orbit. Why a moon so similar in size and distance to Enceladus shows no surface activity was a long-standing puzzle; the newly found ocean suggests the answer may simply be that it has not broken through yet.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.