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Enceladus plumes and the ocean
Enceladus sprays its ocean into space at about 400 m/s from the south pole, faster than the 239 m/s needed to leave the moon.
See it in the tour: chapter ocean beneath ice, shot 8.2.
A small moon with an ocean
Enceladus has a radius of 252.1 km, about 500 km across physics. Its surface gravity is 0.113 m/s², 0.0115 g physics. At the surface the circular speed is 169 m/s and the escape speed is 239 m/s physics.
Under the ice is a global ocean, found from gravity measurements and the moon's slight wobble as it orbits Saturn. The shell may be as thin as 1 to 5 km at the south pole and averages 20 to 25 km physics. Enceladus orbits Saturn at 238,000 km and keeps one face to the planet physics.
What Cassini found
In 2005 Cassini found icy particles and gas erupting from the south pole at about 400 m/s physics. The jets rise from warm fractures in the crust that scientists call tiger stripes physics. The plume is water vapour, carbon dioxide, methane, salts and silica, with organic material about 20 times denser than expected physics. NASA reads this as most of the chemical ingredients for life, and likely hydrothermal vents releasing hot, mineral-rich water into the ocean physics.
The plume speed is above the escape speed. Part of the spray leaves the moon and forms Saturn's E ring physics. Sampling the ring samples the ocean.
The station
The Enceladus South Polar Research Station sits at 55° S, outside the fractures. About 18 researchers and support staff work there. It opened in 2088 fiction. In 2052 a robotic orbiter began flying the plumes repeatedly fiction.
On the reference date the Sun stands 22° high at the station's noon physics. That is a low, hard light with sharp shadows. At the south pole the Sun is 13° below the horizon, so the pole is dark and the plumes rise out of shadow into sunlight, backlit physics.
From the Saturn-facing side, Saturn is about 28° across, with its rings edge-on physics.
Gravity you can throw through
The same legs that jump 0.45 m on Earth would jump 39 m on Enceladus and stay aloft for 53 s physics. The experience caps a jump at 1.1 m, 8.8 s aloft, and a walker moves in low hops design.
The sampling drone
People stay at the station. A robotic drone, V8, flies the plume runs design. It is 2.5 m long and 3 m across, with a dry mass of 300 kg. Its green monopropellant thrusters give a specific impulse of about 250 s. The station is 110 km from the plume source region. The drone has a delta-v budget of 500 m/s for out, sample, back, landing and margin, which needs 68 kg of propellant, 46 litres. Its mass ratio is 1.226 design.
The thrusters make small puffs that are nearly invisible. The sight is the sunlit plume ice.
The station's rules for what the drone may touch are in Planetary protection. The cargo tug that spirals out from Titan is in Electric propulsion.
Key numbers
| Quantity | Value | Basis |
|---|---|---|
| Radius | 252.1 km | physics |
| Surface gravity | 0.113 m/s² (0.0115 g) | physics |
| Circular / escape speed at the surface | 169 / 239 m/s | physics |
| Plume speed | about 400 m/s | physics |
| Ice shell, south pole / average | 1 to 5 km / 20 to 25 km | physics |
| Sun at the station, noon; at the pole | 22°; −13° | physics |
| Station / staff | 55° S / about 18 | fiction |
| Drone mass / delta-v / propellant | 300 kg / 500 m/s / 68 kg | design |
| Station to plume source | 110 km | design |