It's off-white with one large dimple in it. Remind you of anything?
"That's no dwarf planet..."
NASA's Dawn spacecraft has transmitted a series of images of the dwarf planet Ceres - part of its first ever mission to the biggest body in the asteroid belt between Mars and Jupiter. New images of Ceres from the Dawn vehicle Dawn will transmit increasingly sharp images of Ceres - named for the Roman goddess of agriculture …
(1) It's a bit difficult to hollow out a body that likely has a subsurface ocean.
(2) The central pressure of Ceres is about 133 MPa (19,000 psi). That exceeds the strength of typical rock. So if you hollowed it out, it would collapse. In fact, the very definition of dwarf plant is based on being large enough to crush the interior and adopt a round shape. Smaller bodies are notably irregular.
(3) Google wouldn't want a high ping time from Evil HQ to everything they control. At most they would move it to low orbit, among its future constellation of laser death comsats.
"The central pressure of Ceres is about 133 MPa (19,000 psi). That exceeds the strength of typical rock."
Where did you get that value? Or, if you calculated it, would you please share your calculations? I've tried to do that before and didn't trust my approximations of the changing gravity from surface to core.
19,000psi is a bit high, but only modestly higher than the bottom of the Mariana Trench (15,000psi and change). It'd be challenging to have large chambers, but there are existing materials - like high-strength steels - that would tolerate the pressure well.
At a quick approximation, 9-inch thick Aermet 340 or Maraging 350 would give a safety factor of 2 on a long cylindrical chamber 4 yards in diameter. (You might want to apply a 10-20% strength knockdown when using steels that thick, though. They never get heat treated and worked as well as thinner sections.) Spherical chambers of the same diameter and thickness would half the hoop stress, but 12-foot spheres are a bit more cramped for proper Evil Layers at the Center of the mini-Earth.
Obviously, there are some practical challenges beyond pressure and high ping times. It's a bit of a challenge to dig to the center of Ceres (a record-setting tunnel that gets to very high pressures at its base) and work to excavate the core through that probably-narrow tunnel. Then there's the whole of challenges stemming from working on Ceres: near-zero G (centi-G, I guess), vacuum above, low temperatures, and you're probably a long way from the contractors you built your kit so service plans will be expensive. If your Caterpillar 2000X Asteroid Tunneler breaks down, you better hope spares were shipped with it.
One question I couldn't answer with a cursory Google search: what's the estimated temperature at Ceres' core? If it is much warmer than 100C, that's a whole new complication in terms of refrigerating the Evil Layer and maintaining material strength.
Another thought: the compressive strength of granite and basalt do exceed the pressures at Ceres' core, though their ranges are wide (100 - 250MPa and 100 - 300MPa, respectively). That's not a material you'd want for a thin-walled habitat at the center of Ceres, but it's enough that a thick, engineered shell of rock could take some of the load off a steel habitat.
"It's a bit difficult to hollow out a body that likely has a subsurface ocean."
Digging air-filled structures under water is an accomplished engineering feat. You - or at least I - wouldn't want to depend on asteroidal regolith and ice to hold a 14.7psi atmosphere, so the walls would need to be sealed in any case.
Dwarf planets are not planets. Planets are objects massive enough to be shaped by gravity (tick), not undergoing nuclear fusion (tick), cleared out all the space around the object of smaller objects (fail).
It's like saying "If Bob is a gorilla, and Bill is a gorilla, how many humans in this room?!"
There are 8 planets. If you are including dwarf planets as planets 10 is way off...
As of Tue Jan 20 2015 there are:
10 objects which are nearly certainly dwarf planets,
22 objects which are highly likely to be dwarf planets,
44 objects which are likely to be dwarf planets,
75 objects which are probably dwarf planets, and
359 objects which are possibly dwarf planets.
...cleared out all the space around the object of smaller objects (fail).
I think that's a pretty sad classification as defining something like a planet in terms of things in its environment like this doesn't seem to work very well. Cleared surrounding space of smaller objects? For what distance? For what period of time? What about moons? Rings? Is orbiting a star a requirement? If we introduce a bunch of asteroids in a planet's orbital path through some cosmic event, would the planet get kicked out of the the big planet's club until it cleaned up its act?
It's a stupid, made-up controversy!
Stars are classified based on their physical characteristics (spectral make up, size, et cetera). If we are going to say that Pluto is a dwarf planet and call it that, why persist in calling both Mercury and Jupiter simply by the name planet? They are sufficiently different enough to merit separate classifications, too.
...cleared out all the space around the object of smaller objects (fail).
The new definition has always bothered me because Pluto's orbit crosses that of Neptune, which surely means Neptune hasn't cleared its orbit of smaller objects, which surely means Neptune is merely a dwarf planet and not a proper planet? Yes I'm aware of the resonance which means Neptune and Pluto don't collide, but still... crossing orbits!!!
I would like to know how you know that the heating from radioactive decay would be minuscule. On Earth the heat escaping isn't more than 7 TW and it is a lot bigger and the crust is quite thin, I would expect the loss of heat would go a lot slower the thicker the crust is. The Earth being bigger means of course that it also has a lot more heat stored and radioactive material to heat it up. However 7 TW isn't all that much and this is with a planet with core that is molten due to the heat. Also the interior of Ceres would only need to be kept maybe fifty degrees warmer than it's mean surface temperature to keep water with a dash of anti-freeze liquid. So, how do you know the radioactive heating would be minuscule?
Also you can throw in the pressure that affects the freezing point a little.
The highest pressure would be at the center. Ceres has a low density, so it's probably mostly ice. Radioactive materials are heavy, so any radioactive heating would have to come from a small, rocky core. If the core is rocky, it's not an ocean. Also, heating a planet by radioactivity depends on a smaller surface area to volume ratio to hold in the heat. Ceres is probably too old to still have any radioactive heating.
Ice under high pressure CAN be liquid down to around -20C (but at a higher pressure than calculated above). Surface temperature of Ceres is estimated in the range -70C to -140C. If the core is rocky any liquid water would have to be closer to the surface, and possibly under insufficient pressure to melt the ice even if there is still some core heating. Things are in the ballpark but the odds are small. See the following factoid:
The minimum temperature that liquid water can exist without ever freezing is -21.985 °C at 209.9 MPa; at higher pressures water freezes to ice-three, ice-five, ice-six or ice-seven at increasing temperatures.
Thanks for answering.
As I understand it all the heavier elements are made in supernovas, and this is the only known source for them. This would then mean most of the radioactive elements. There is of course radioactive decay which in a sense make new elements, but the start of these chains of decay has to be made in a supernova. Nearly nothing affects the half life of these elements and all of this material in this solar system was made before it formed. So there should be no difference between the radioactive elements in Ceres as that on Earth. The original amount will of course be different. There are four main decay chains where one is extinct in this solar system (or nearly). Whether it is enough to heat Ceres to any significant degree however I do not know, but I still see no reason why it shouldn't be so.*
About your last factoid. How does that turn out with any anti-freeze thrown into the mix? Salt or ammonia for instance?
*This does not of course mean that there is no such reason. I am a firm believer that my understanding of the science does not have any impact on how it actually is.
"About your last factoid. How does that turn out with any anti-freeze thrown into the mix? Salt or ammonia for instance?"
Potentially quite a bit. Speaking of just 1 bar conditions:
Plain old NaCl lowers the freezing point a bit for thick brines, while calcium chloride can give a a -52C freezing point. However, that'd require improbably large quantities of halogens. At 32% ammonia, if I read the phase diagram correctly, you can keep a water solution liquid to -100C. High ammonia concentrations are more likely than hypersaline conditions in asteroids because nitrogen and, obviously, hydrogen are fairly abundant in the universe compared to calcium and chlorine.
Advanced mass , temperature and neutron emissions measurements will be made. It is maddening to have to wait, but that is the nature of exploration.
I am betting on liquid water near the metallic core, heated by fission and insulated by 200 kilometers of ice. And ice. A thin coating of concrete. And many, many caves where asteroids pierced the concrete and the sun excavated a nice hidey hole for a colony.
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