My understanding is that we've known for a long time that they range from a sooty snowball to a single chunk of pitted iron alloy. Looks like this one was a softie.
That’s true, but I’m thinking that every class of asteroid is going to go down a level or two on the scale once we actually go poke them. Look at Bennu: they expected from the estimated density that it was a conglomerate and would have a significant amount of surface sand and dust they could pick up.
Close up pictures showed that it is a lot less homogeneous than they expected, with huge boulders right on the surface as well. That doesn’t match with the measured mass and density since boulders are heavy and dense, but maybe there are more internal voids. But then when they touched it, the nitrogen gas that was supposed to blow some dust and sand into the collection chamber also threw a huge amount of material out and away from the probe. It may even have shattered some of the gravel, meaning that stuff is really more like styrofoam. It may still be silicates, but it is probably foamy. Think of pumice rather than sandstone or granite. Those giant boulders might be more like stage props than actual boulders. It will be very interesting to see what that stuff looks like when they get the samples back.
All those stories of hollowing out an asteroid and turning it into a habitat or generation ship for 50,000 people aren’t looking so prescient. :)
Of course on the other hand it could turn out to just be selection bias: sample return missions are obviously going to pick a low–density asteroid that they hope will at least have some dust they can scoop up, instead of picking a really dense one that might turn out to be too difficult to collect from.
Also, I’m ignoring the dwarf planets that happen to be in the asteroid belt, like Ceres. We can reasonably expect them to have some real rocks.
> All those stories of hollowing out an asteroid and turning it into a habitat or generation ship for 50,000 people aren’t looking so prescient. :)
It would be very interesting to figure out how far away we are from the technology to send a "Seed" probe to a large conglomerate asteroid, designed to replicate itself into thousands of builder-bots. Then the builders would slowly but surely turn the asteroid into millions of assembler-chunks consisting of layers of concrete and metal. Then those assemblers would connect to each other, turning into sections of habitat hull.
Basically do it like Mother Nature does it: tiny building blocks that self-assemble into bigger building blocks that self-assemble into bigger building blocks, over and over. In other words, proteins into DNA/lipids/etc, DNA/lipids/etc into organelles, organelles into cells, cells into muscles/organs/etc. Not saying it would be squelchy organic technology, just that the process would look similar from a high level. Maybe it would look like self-assembling Lego!
Seed probe -> Processing-bots -> raw material -> fibrous, metallic, and concrete-like Assemblers -> various types of building blocks.
> It may even have shattered some of the gravel, meaning that stuff is really more like styrofoam. [...] All those stories of hollowing out an asteroid and turning it into a habitat or generation ship for 50,000 people aren’t looking so prescient. :)
Even simpler then, insert giant balloon in the middle, pump it up, cover walls with concerete and you have habitat, no expensive drilling and hollowing out.
What would you gain in that situation? Just some radiation shielding. Most stories about hollowing out asteroids wanted to gain at least some structural rigidity, which in your scenario comes entirely from the concrete you have to ship into space. Ideally you would want to melt the asteroid and blow it up to kilometers across and/or spin it for artificial gravity. Heating and melting foam is harder than solid rock or metal, and spinning it is useless if it has no strength in tension.
Structural rigidity in space is 99% tension and 1% compression, due to the lack of gravity, and I'm being generous to compression here. Rock is good at hold itself up against gravity, but is very poor at retaining an atmosphere compared to, say, UHMWP aka Dyneema.
Hollowing out an asteroid is more about raw materials and micrometeorite/particle shielding, both of which a slushy will provide in abundance.
In that case: blow up the balloon, melt rock outside balloon. You could make "cement" from grinding local material plus some binder, that way you bring in less mass. Radiation shielding is also a nice use for asteroid's mass. I'm just saying that blowing up a balloon is easier than extracting several cubic kilometers of rock from inside of asteroid. You can start from that premise and try to find some solutions.
> Heating and melting foam is harder than solid rock or metal
You can grind it, then blow it with very hot gas onto your baloon, making a nice melted coat of rocks. This technique is already used to repair metal rotor shafts, it deposits machinable metal: https://www.youtube.com/watch?v=NAeBpF84Q9M
Humans need room–temperature nitrogen, not nitrogen plasma. You would rapidly make the atmosphere inside your bubble unlivable. There are few easy solutions here.
Then you wait a moment until it cools down. Of course there are few easy solutions, space is very hard environment mercilessly waiting for you to make an error. You can find problems in every step. It doesn't mean you should give up before you start.
> All those stories of hollowing out an asteroid and turning it into a habitat or generation ship for 50,000 people aren’t looking so prescient.
If it's as loose as that then you could just put an inner steel "pressure" hull (the actual pressure from the outside would be negligible but it'd have to be able handle a human compatible air pressure) inside the asteroid and use the asteroid material as a radiation shield instead I guess.
Would work for a base but not for a ship with any appreciable thrust would shed material.
Worth noting that those "soft and fluffy" clumps of gravel and sand still move at 18+km per second and even one the size of Dimorphos striking the earth would easily cause an explosion big enough to completely level even the largest city (think 30 to 50 megatons of explosive energy upon impact). Or for example a comet, -mostly just a sort of dirty snowball- a couple miles in diameter would cause a global climatic catastrophe and vaporize every living thing and standing structure within hundreds of miles of its impact location.
Terrifying capabilities for such soft and fluffy, brittle things.
