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Asteroids are apparently a lot softer and fluffier than we thought. More like gravel and sand clumped together rather than being giant boulders.

by db48x 4y ago

samatman 4y ago
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.
- db48x 4y ago
  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.
  - yetihehe 4y ago
    > 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.
    - db48x 4y ago
      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.
      - yetihehe 4y ago
        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 https://www.youtube.com/watch?v=NAeBpF84Q9M
        db48x 4y ago
        That would be very fun, but also a lot of gas to ship up from Earth :)
senectus1 4y ago
SOME
gl-prod 4y ago
Yeah, some asteroids don't have enough gravity to turn those gravel and sand into solid base.
demarq 4y ago
Not really, the impact was at 23000 kilometres per hour. The live coverage just made it look slow and small.
helloworld11 4y ago
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.

Asteroids are apparently a lot softer and fluffier than we thought. More like gravel and sand clumped together rather than being giant boulders.

by db48x 4y ago

Asteroids are apparently a lot softer and fluffier than we thought. More like gravel and sand clumped together rather than being giant boulders.

samatman 4y ago

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.

db48x 4y ago
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.
- yetihehe 4y ago
  > 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.
  - db48x 4y ago
    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.
    - yetihehe 4y ago
      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 https://www.youtube.com/watch?v=NAeBpF84Q9M
      - db48x 4y ago
        That would be very fun, but also a lot of gas to ship up from Earth :)

senectus1 4y ago

SOME

gl-prod 4y ago

Yeah, some asteroids don't have enough gravity to turn those gravel and sand into solid base.

demarq 4y ago

Not really, the impact was at 23000 kilometres per hour. The live coverage just made it look slow and small.

helloworld11 4y ago

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.