Ceres

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Planet Ceres (a dwarf planet). Located in the main asteroid belt between Mars and Jupiter it is the nearest big "waterworld" to Earth and perhaps a very attractive target for colonization. Ceres is about 1000km in diameter and the only object in the asteroid belt that is spherical due to it's own gravity. Ceres is similar in size to Saturns moon Thetys (see above image for scale). Image Credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA / Justin Cowart


Why may Ceres be interesting in regards to advanced APM and colonization?

  • The challenge of exploring and eventually exploiting cryovolcanic channels robotically.
  • colonization and a space gas station (electrolysis of water and production of methane)

Some trivia about Ceres

  • Ceres is a (dwarf) planet (just like Pluto and its moon Charon).
  • Ceres is the largest asteroid in the asteroid belt in the gap between Mars and Jupiter where
    one would maybe expect a planet if it weren't for the large gravitational disturbances of Jupiter.
  • Ceres is one on the bodies in our solar system where liquid water is present in underground cracks. There is stark evidence for that due to the very conspicuous young white spots that are cryovolcanic salt deposits. A subsurface water ocean like on Enceladus, Europa and perhaps Titan, Ganymede, and Callisto is not expected, but not entirely excluded as of yet (2021).

Exploration Cryovolcanism

What could we find there?

  • (1) Muddy possibly visous sludge more like Earth's mud volcanues?
  • (2) Crystal clear water more like Earth's Geysers?

From the bright white deposits the latter seem more likely.

  • (1) would make exploration rather challenging
  • (2) would make exploration much easier

Colonization of Ceres

Unlike on our moon there are plenty of volatile elements as raw materials available.
Don't be fooled by the grey cratered similar appearance.
Ceres is very very different from our moon.
Small asteroids of the main belt are the same distance from the sun as Ceres but
they may have a harder time to hang on to their volatiles due to their lower gravity and smaller diameter.

Directly exposed water ice in space (when not really far from the sun) sublimates and gets blown away by the solar wind.
Maybe volatile ices can be found right under a very thin more silicatic regolith dust cover from asteroid impacts though.
We've seen that on the (even closer to the sun) Mars but there way higher gravity (and a somewhat notable atmosphere) is present.
Gravitative differentiation also may have concentrated the lighter less dense more volatile elements on the outer parts of the planets volume.

Underground ambient pressure unpressurized bases for human activities

Wikipedia lists:

  • equatorial surface gravity: 0.28 m/s2 = 0.029 g
    This means a 100kg person would way there just 2.9"kg" (what an earth scale erroneously would show – scales should show Newton)
  • mean density 2.162±0.008 g/cm3 (Earth upper crust 2.69 and 2.74 g/cm3)
  • (model dependent) crust density 1.25 to 1.95 g/cm3
  • (model dependent) core density 2.46 to 2.9 g/cm3

The one Earth atmosphere pressure depth level

At the right depth level in Ceres' crust the water of cryo-volcanic (or artificuially molten) channels could fulfill the pressurizing function that on Earth is fulfilled by air. That is an underground base at the right depth would need no airlock. A down facing port into a cryo-volcanic (or artificially molten) channel can suffice. A door against excessive air humidity and eventually unpleasant toxic gasses filling the whole station may still be advisable though. This is very much NOT like a submarine since the pressure of the water outside and the air inside are equally 1bar. So there is no need for thick sturdy and heavy submarine like walls resisting an implosion.

Ice diving in very cold briny water with earth ice diving dry-suite equipment might be borderline possible. <vr> But likely not a good idea though. This calls for specialized suites that remove any and all discomfort from ice diving.
See: Gem-gum suits.

Artificial channels far from natural cryo-volcanic channels likely need to be filled
with synthesized air (of the same pressure as the surrounding ice-rock) to prevent re-freezing and collapse.
No need for ice diving in these channels

It's exactly 1bar only for exactly one depth though.
So what is the depth range that would be nice for human physiology?

The human physiology depth range

Earth at 5000m ~0.5bar is pretty much the lower limit that humans can endure over extended periods of time (not healthy though).
Oxygen rich air can help but comes with known unpleasent risk of fires becoming much more dangerous.

Earth at -5000m (not reachable ~-4000m is the limit ATM) would be ~2bar. As to the upper limit:
In contrast to diving (short to medium time exposure to high overpressure),
the effects of long time exposure to only slight overpressure on human physiology are largely unexplored (are they really??).
The poor souls that are deep mine workers on Earth are additionally exposed to high temperatures an hard physical work.
Also they come up regularly (more details to check).

Numbers:

On Earth water pressure reaches 1bar overpressure at 10m depth (adding to the already 1bar of the atmosphere making it 2bar).
On Ceres water pressure reaches 1bar overpressure at 34.5 times the depth 345m (since the 1g/0.029g = 34.5)
That is when assuming cryovolcanic channels with a density of salt water not much above 1kg/liter.
If water pockets are closed to the surface then pressures might be higher and closer to what the density of the crust causes.
For Ceres that is about double the pressure at the same depth or equivalently half the depth for the same pressure.

  • Earth 5000m height (in air) 0.5bar – Ceres 172.5m depth (under water)
  • Earth sea level 1.0bar – Ceres 345m depth (under water)
  • Earth 5m depth (under water) 1.5bar – Ceres 517,5m (= 345m * 1.5) depth (under water)

That gives a layer of 345m thickness in Ceres' crust that is suitable for human physiology in unpressurized stations and diving suites over longer durations of time.
Note that this is assuming a channel open to the surface and stable self supporting channel walls. At least a slight crust must be there though since liquid water cannot exist in vacuum.

The unpressurized briefly visitable deph range

More extreme depths borderline acceptable for brief visits:
Multiply the following by 34.5 (or half of that for 2g/ccm density) to get the corresponding depths for Ceres:

  • scuba diving 20m (beginners) 50m (more risky experienced) 120m (highly risky buisness with special equipment)
  • saturation diving record depth Earth ~200m (typical) ~700m (highly risky buisness)

700m * 34.5 = 24.15km (or 12.075km)

Synthesis of Air

Oxygen is easy: Direct synthesis from water.
Nitrogen may be a bit more tricky:
To make nitrogen there's a need to find some ammoniak ice (or other easily processable nitrogen rich compounds).
Amonniak is even more volative than water.
It will be interesting to see if and where it will be found.
Molecular nitrogen is only retained at bodies way out the solar system (Titan, Triton, Pluto, TNOs, ...)

Very deep mining made possible by Ceres' very low gravity

How deep could we mine on Ceres?

Earth's deepest mine (a gold mine) is about 4000m=4km deep.
Assuming for Ceres the depth that can be mined down to the material has the same density as Earth's upper crust
(which seems like a conservative estimation) then the same pressure is reached 1g/0.029g = 34.5 times the depth 138km (46000 3m high floors)

This might be hugely off though since:

  • Heat might be much less of a challenge than on Earth (allowing for much deeper mining)
  • Glacial flow of material might be a big challenge (allowing for much less deep mining)

Creation and maintenance of artificial underground tunnel channels

The material being quite water ice rich may be quite soft and rater easy to dig through.
Mining by melting and pumping might work well.

Artificial molten channels far from cryovolcanic site will likely
refreeze fast if not permanently heated with unholy amounts of energy.
Filling channels with dry on site synthesized air at the same pressure as the surrounding ice-rocks might be an option to prevent refreezing.
Gas might diffuse out over large exposed ice-rock surface areas.
A very thin sealing foil against gas escape should suffice though.
Given there is a prssure equilibrium channels won't shrink in diameter through glacial flows.
Shearing and deformations through glacial flow might occur though.
So active dynamic work may be needed to maintain underground artificial channel systems.
Ceres cryololcanic activity seems pretty limited though compared to say Enceladus cryovolcanic activity. So glacial shearing flows may be rather limited which would be beneficial.

How deep could we drill into Ceres (the center?)

On Earth the record was near 14km.
Conservatively assuming same density as Earth's crust Ceres' corresponding depth would be 14km * 34.5 = 483km.
This pretty much all the way down to Ceres' innermost center.
That is if temperatures are not too high down there then probably
it's likely possible for us to drill down all the way down to the (weightless) core.
And that even with conventional technology. With gemstone metamaterial technology this should be easy. Again if temperatures are reasonable.

Expectable pressures down there (assuming 2kg/liter) are high but still reasonable.
Note that gravity drops of to weightlessness, so this needs to be integrated.
TODO make an estimate.

Related

External links

Awesome picture of a cryovolcanic vent:

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