Moons · Space Codex
Mimas
A small, battered moon dominated by Herschel crater, a third of its own width.
The 'Death Star' moon with a hidden ocean
At a glance
Key points
In 2024 its wobble revealed a surprise: a young ocean beneath the ice.
- Herschel crater is a third of the moon's width
- Hides an ocean only about 5–15 million years old
- Its gravity clears the Cassini Division in Saturn's rings
Surface
Herschel crater is so large relative to Mimas that the impact nearly broke the moon apart. Its central peak rises about 6 km from the floor, close to the height of Everest above sea level, on a world only about 400 km across. The rest of the surface is saturated with smaller craters.
A stealth ocean
Careful tracking of Mimas's orbit and the tiny rocking of its spin with Cassini data showed in 2024 that it must hold a global ocean 20–30 km down. The ocean is so young, roughly 5–15 million years old, that it has not yet had time to crack the surface.
Shaping the rings
Ring particles at the inner edge of the Cassini Division orbit Saturn exactly twice for each orbit of Mimas. The repeated tug clears the 4,700 km-wide gap between the A and B rings.
What we still don't know
What melted the interior so recently, and whether the ocean will eventually freeze again or keep growing.
Missions
- 1977–
Jupiter 1979, Saturn 1980; interstellar space since 25 Aug 2012.
- 1997–2017
Cassini–Huygens
NASA / ESA / ASICompletedOrbited Saturn 2004–2017 and ended by diving into the planet.
First-hand · our 3D model
How we render it
Mimas is a sphere wrapped in a global map built from USGS and NASA spacecraft mosaics.
It is drawn at about 2.4% of Saturn's radius, enlarged from its true 0.34% so it stays visible. It orbits in Saturn's equatorial frame, inclined 1.6°, with a 22.6-hour period kept in true ratio to its neighbours, and keeps one face towards Saturn.
Moon sizes and orbits are compressed so a whole system fits on screen, but never reordered: each moon is drawn at 0.72 × (true size ratio)^0.6 of its planet, capped so no large moon is drawn bigger than it really is, and orbit distances are log-compressed into a band that clears the planet's rings. Orbital periods keep their true ratios, every moon is tidally locked, and on lighter devices only the two largest moons of each planet are drawn.
Related entries
Sources
- NASA NSSDC Saturnian Satellite Fact Sheet (opens in a new tab)
- JPL Solar System Dynamics: satellite physical parameters (opens in a new tab)
- JPL Solar System Dynamics: satellite mean orbital elements (opens in a new tab)
- NASA Science: Mimas (opens in a new tab)
- Lainey et al. 2024, Nature (summary) (opens in a new tab)
Last reviewed against these sources. Built from public NASA, ESA and JPL data; not affiliated with or endorsed by any agency.