Mimas
The Death Star
The moon with a giant crater that looks exactly like the Death Star, orbiting in 23 hours
🌙 Mind-Blowing Fact
Mimas has the Herschel crater - 130 km wide on a 400 km moon! It looks EXACTLY like the Death Star from Star Wars! The impact almost destroyed Mimas. One more hit that size and it would have shattered!
What is Time on Mimas?
What is Time on Mimas?
Mimas is Saturn's innermost major moon, famous for its resemblance to the Death Star. From a TIME perspective, Mimas offers rapid 23-hour cycles with spectacular ring views and the constant reminder that one more big impact could shatter this fragile moon.
The 23-Hour Day
- One Mimas orbit = 22.6 hours (0.94 Earth days)
- Saturn's rotation = 10.66 hours
- Result: Watch Saturn rotate ~2.1 times per Mimas orbit
- Almost Earth-day length - most human-friendly!
The Death Star Crater
Herschel crater defines Mimas:
- 130 km diameter on a 400 km moon (1/3 the diameter!)
- 10 km deep
- Central peak 6 km high
- Impact energy: Nearly shattered Mimas
- Created: Shock waves and fractures on opposite side
Time almost ended for Mimas with that impact. It survives by chance.
Saturn's Ring View
At 185,000 km from Saturn:
- Rings dominate the sky - edge-on from Mimas's equator
- Saturn appears 25x larger than Moon from Earth
- Ring shadows visible on Saturn
- Spectacular eclipses when Mimas enters Saturn's shadow
The Cassini Division Shepherd
Mimas's orbital resonance shapes Saturn's rings:
- 2:1 resonance with ring particles
- Creates Cassini Division - largest ring gap (4,800 km wide!)
- Time synchronization: Ring particles at Cassini Division orbit twice per Mimas orbit
- Gravitational clocking: Mimas's gravity "clears" the division
Time on Mimas is written into Saturn's rings themselves.
The Fragile Moon
Mimas is barely holding together:
- Low density: 1.15 g/cm³ (mostly water ice with some rock)
- Not fully differentiated: Mixed ice/rock throughout
- Herschel impact: Created fractures throughout moon
- One more hit: Similar impact would shatter Mimas completely
The Near-Destruction Clock
Herschel crater formed ~4 billion years ago:
- Impact moment: Nearly destroyed Mimas
- Shock waves: Visible as grooves on opposite side
- Survival: By mere chance (a bit more energy = complete destruction)
- Since then: 4 billion years of "borrowed time"
Mimas is a moon living on borrowed time since the impact that almost killed it.
A Day in the Life
The Death Star Moon
You land on Mimas at the edge of Herschel crater. Saturn and its rings fill half the sky. You're standing on the solar system's most famous crater - the one that makes Mimas look exactly like the Death Star.
The Crater
"Don't fall in," jokes Commander Williams.
You're standing at the rim of Herschel crater. It's 130 kilometers across - one-third the diameter of Mimas itself. Ten kilometers deep. At the center, a mountain 6 kilometers tall.
"This impact almost destroyed Mimas," Williams explains. "A bit more energy and Mimas would have shattered into a ring around Saturn. We're standing on a moon that survived by luck."
The 23-Hour Day
"One Mimas day is 22.6 hours," Williams says. "Almost exactly one Earth day. Of all Saturn's moons, Mimas is the most human-friendly timescale."
Hour 0-11: Morning/afternoon (Saturn rotates once)
Hour 11-23: Evening/night (Saturn rotates again)
"We watch Saturn spin twice per day," she continues. "It's spectacular. Rings and all."
The Ring View
You look up. Saturn dominates the sky - massive, with rings stretching from horizon to horizon.
"We're close to Saturn's equator," Williams explains, "so the rings are nearly edge-on from here. But you can see them extending into space, reflecting sunlight."
Saturn appears 25 times larger than the Moon from Earth. The rings glow. You can see the Cassini Division - the dark gap in the rings.
"Mimas created that gap," Williams says proudly. "Our gravity. We orbit twice for every orbit of particles in the Cassini Division. The resonance cleared it out. Time synchronization between Mimas and the rings."
The Death Star Resemblance
"The resemblance is uncanny," Williams admits, showing you satellite photos.
Mimas from space looks EXACTLY like the Death Star from Star Wars: spherical, heavily cratered, with one enormous crater (Herschel) that looks just like the Death Star's superlaser dish.
"Star Wars came out in 1977," she says. "Voyager 1 photographed Mimas in 1980. George Lucas couldn't have known. Pure coincidence. But everyone calls us the Death Star moon now."
The Near-Death Experience
Dr. Kapoor, a geologist, explains the Herschel impact.
"About 4 billion years ago, something big hit Mimas. Maybe a 10-kilometer asteroid. The impact was catastrophic."
She shows you models. The asteroid hit with enough energy to almost shatter Mimas completely.
"See these fractures?" She points to cracks radiating from Herschel. "Shock waves from the impact. On the opposite side of Mimas, there are grooves and chaotic terrain from the shock wave converging."
"One more hit like that," she says quietly, "and we wouldn't be here. Mimas would be rubble. Another ring around Saturn."
Living on Borrowed Time
"Mimas has been on borrowed time for 4 billion years," Kapoor continues. "The Herschel impact should have destroyed us. But it didn't - just barely. We're a moon that cheated death."
You look at Herschel crater - this enormous wound that nearly killed the moon you're standing on.
"Every day here," Kapoor says, "is a day Mimas shouldn't exist. We're living on a corpse that refused to die."
Saturn's Rapid Rotation
That night (hour 14 of the Mimas day), you watch Saturn.
Every 10.66 hours, Saturn completes one rotation. You've already watched one full rotation since sunrise. Now you're watching the second.
"I use Saturn's rotation as my clock," Williams says. "First rotation: morning. Second rotation: afternoon/night. Then sunrise and repeat."
The rings cast shadows on Saturn. Cloud bands flow across the planet's face. The Great White Spot (when visible) comes around every 10.66 hours.
"Watching Saturn never gets old," Williams admits.
Children of Mimas
A child approaches - she's 3 Earth years old, born on Mimas.
"I'm 1,200 days old!" she announces.
She's counting Mimas days (22.6 hours each). For her:
- One Mimas year ≈ 387 Mimas days = 358 Earth days
- Her 3rd Earth birthday = 1,220 Mimas days
"Do you know about the crater?" you ask.
"Herschel?" She nods seriously. "That's where the asteroid almost killed Mimas. But we survived!"
The Ring Shepherding
Dr. Lee, an orbital dynamics specialist, explains Mimas's role.
"See the Cassini Division? That dark gap in Saturn's rings? Mimas created that."
"How?"
"Orbital resonance. Ring particles in the Cassini Division complete two orbits for every one Mimas orbit. The 2:1 resonance means Mimas's gravity tugs on them at the same point every two orbits. Over time, that clears out the ring material."
"Mimas is a clock synchronized with the rings," she continues. "Every 22.6 hours, Mimas completes one orbit. Every 11.3 hours, particles at the Cassini Division's outer edge complete one orbit. Perfectly synchronized."
Time on Mimas is time written into Saturn's rings.
The Fragile Structure
"Mimas is fragile," Kapoor explains. "Low density - 1.15 g/cm³. Mostly water ice with some rock mixed in. Not fully differentiated. And the Herschel impact created fractures throughout the moon."
"Another impact that size," she says, "and Mimas would shatter. We'd become a new ring of Saturn. The Death Star would finally be destroyed."
"So we monitor asteroids carefully. Very carefully."
Eclipse Watch
"Eclipse in 30 minutes," announces the station AI.
Every 22.6 hours, Mimas passes into Saturn's shadow. Temperature drops. Darkness falls despite the "sun" being visible.
You watch. Saturn's shadow approaches - a curved darkness crossing space. Then - shadow. Two hours of eclipse.
"During eclipse," Williams says, "we see Saturn's auroras. Green and blue lights at the poles. Beautiful."
In the darkness, Saturn glows with aurora light. The rings are faintly visible in reflected light. Stars appear.
Then - emergence. Sunrise. Another 22.6-hour day begins.
Time's Fragility
As you prepare to depart Mimas, you understand.
This moon is:
- Barely intact: One impact away from destruction
- Living on borrowed time: Should have shattered 4 billion years ago
- Synchronized with rings: Time written into Saturn's structure
- Almost Earth-day length: 23-hour cycles feel natural
"We're the Death Star moon," Williams says, looking at Herschel crater. "But unlike the Death Star, we're fragile. Vulnerable. One more hit and we're gone."
She pauses.
"But we're still here. 4 billion years after the impact that should have killed us. Time keeps flowing. Mimas keeps orbiting. The rings keep turning. And we keep watching Saturn spin, twice per day, on a moon that refuses to die."
Thought Experiments
What if the Herschel impact had been 10% stronger?
Mimas would have SHATTERED! The pieces would have: 1) Spread into a new ring around Saturn, 2) Some pieces would have crashed into Saturn, 3) Some would have hit other moons, 4) The Cassini Division would never have formed (no Mimas to create the resonance!), 5) Saturn would have a much more spectacular ring system (from Mimas debris). We came within 10% of Mimas not existing. The entire Saturn system would look different. Time literally balanced on that impact!
How would the 2:1 ring resonance affect ring particle "time"?
Ring particles at the Cassini Division orbit in 11.3 hours - exactly HALF of Mimas's 22.6-hour orbit. They experience: 1) Mimas's gravity tug at the SAME point every 2 orbits, 2) Synchronized perturbation, 3) Gradual clearing of the division, 4) Their "year" is perfectly synchronized with Mimas as a 2:1 ratio. If you lived on a ring particle there, Mimas would appear at the same position in the sky every 2 days. Perfectly predictable. Time locked to Mimas's orbit!
What would "Death Star tourism" be like?
Tourists would come specifically to stand IN Herschel crater and take photos! "I stood on the Death Star's superlaser dish!" Tours would include: 1) Hike to Herschel's central peak (6 km tall), 2) View fracture zones from impact, 3) Visit opposite side to see shock-wave terrain, 4) Watch Saturn and rings from crater floor (best view!), 5) Take the mandatory Death Star comparison photo. T-shirts: "I survived Herschel crater!" Mimas would be the most-visited Saturn moon for pure pop culture value alone!
The Science of Time on Mimas
The Science of Time on Mimas
Herschel Crater: The Near-Destruction Event
Herschel crater statistics:
- Diameter: 130 km (1/3 of Mimas's 396 km diameter!)
- Depth: 10 km
- Central peak: 6 km tall (comparable to Mt. McKinley on Earth!)
- Age: ~4 billion years old (primordial)
- Impact energy: ~10²⁴ joules (equivalent to 10 trillion tons of TNT)
Why Mimas Survived
Mimas barely survived because:
1. Impact angle: Likely a grazing blow (not head-on)
2. Mimas's size: Just large enough to absorb the shock
3. Internal structure: Fractures absorbed energy instead of shattering
4. Luck: 10-20% more energy would have destroyed Mimas
Evidence of near-destruction:
- Fractures: Radiating from Herschel across the surface
- Opposite-side terrain: Grooves and disrupted regions from shock-wave convergence
- Heat damage: Melting and reformation of ice in impact region
The 2:1 Orbital Resonance
Mimas creates the Cassini Division through 2:1 resonance:
The mechanism:
1. Ring particles at the Cassini Division orbit in 11.3 hours
2. Mimas orbits in 22.6 hours (exactly 2:1 ratio)
3. Every 2 orbits, particles experience Mimas's gravity at the SAME point
4. Cumulative perturbations clear ring material from this region
5. Result: 4,800 km wide gap (largest ring division)
This is direct evidence of time synchronization in the Saturn system.
Internal Structure
Mimas's composition:
- Density: 1.15 g/cm³ (water ice = 0.92, rock = 2.5-3.5)
- Composition: ~75% water ice, ~25% silicate rock
- Not differentiated: Mixed ice/rock throughout (unlike larger moons)
- Porous structure: ~10-20% voids/fractures
This low density makes Mimas fragile - another major impact would likely shatter it.
Tidal Heating (Minimal)
Unlike Enceladus (active geysers), Mimas has:
- No geological activity: Cold, dead interior
- Minimal tidal heating: Orbit too circular
- No resonances: With other moons that would generate heating
Why the difference? Mimas's orbit is too circular and not in major resonances, so tidal flexing is minimal.
Orbital Mechanics
Mimas's orbit:
- Semi-major axis: 185,539 km (inside Enceladus at 238,000 km)
- Orbital period: 0.942 days (22.6 hours)
- Orbital velocity: 14.32 km/s
- Inclination: 1.57° (nearly equatorial)
Saturn's Ring Structure
Saturn's rings, shaped by resonances:
- C Ring inner edge: Titan 1:0 resonance
- Cassini Division: Mimas 2:1 resonance (most prominent!)
- Encke Gap: Pan (moon within gap) clears it
- Other divisions: Created by resonances with other moons
Mimas is responsible for the most visible feature in Saturn's rings.
Temperature Profile
Mimas temperatures:
- Subsolar point: -180°C (warmest)
- Night side: -220°C
- Eclipse: Drops to -220°C in minutes
- Average: -200°C
With 22.6-hour days, temperature swings are moderate compared to shorter-period moons.
The "Death Star" Coincidence
Timeline of the resemblance:
- 1977: Star Wars released, featuring the Death Star
- 1979: Pioneer 11 flyby (low-resolution images)
- 1980: Voyager 1 flyby captures clear images of Herschel crater
- Public reaction: "It's the Death Star!"
Pure coincidence - George Lucas couldn't have known about Herschel crater when designing the Death Star.
Future Evolution
Mimas's future:
- Stable orbit: No significant evolution expected
- No more major impacts: (statistically rare in current solar system)
- Slow cooling: Interior gradually cooling over billions of years
- End state: Frozen, dead moon orbiting Saturn until sun's death
Comparison with Enceladus
Both are mid-sized Saturn moons, but vastly different:
| Feature | Mimas | Enceladus |
|---------|-------|-----------|
| Distance | 185,539 km | 238,020 km |
| Orbit | 22.6 hours | 33 hours |
| Activity | None (dead) | Active geysers! |
| Heating | Minimal | Significant tidal heating |
| Surface | Ancient, cratered | Young, smooth regions |
Why so different? Enceladus is in a 2:1 resonance with Dione, creating tidal heating. Mimas has no such resonance.
Time on Mimas is frozen - an ancient, battered moon that survived one impact too many, now orbiting in synchrony with Saturn's rings, marking time in 23-hour cycles while bearing the scar of its near-death experience 4 billion years ago.