6 ms·

This is a profoundly dumb summary of the referenced research article - rather astonishing for UCLA. Studying the boulder swarm - amazing! Saying the boulders

This is a profoundly dumb summary of the referenced research article - rather astonishing for UCLA. Studying the boulder swarm - amazing! Saying the boulders that came off are like shrapnel from a hand grenade - sure. Observing that the boulders keep the relative velocity of the original body and that they could cause damage if they hit something... ok yeah? Interplanetary velocities are energetic - true - and that this is similar to the energy of the Hiroshima atomic bomb - technically true also, but this is where it veers into sensationalism. It's rather telling that this part is put as "Jewitt said" but not quoted. This could very mean that Jewitt said it would have X amount of energy, and the author decided to put in the nuclear bomb angle because it was a similar energy. Asteroids this size just burn up. "In theory" they could hit something in orbit but space is mind-bogglingly huge and this is exceedingly unlikely. And weighed against surface impact of something judged worthy of a planetary defense scenario? Unanticipated risks?

sproketboy 3y ago
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RosanaAnaDana 3y ago
Wouldn't breaking up a planetary defense worthy asteroid into medium to even large boulder size asteroids be considered a win? Whats the limit on asteroid size that can make it through the atmosphere? And even then, intuitively, it would seem like the destructiveness is going to scale with the size of the individual asteroid, so a rain of many smaller asteroids making it to ground would be far lower than one large asteroid..
- icegreentea2 3y ago
  It depends on what the threshold for 'planetary defense worthy' is I guess. If you shattered an asteroid, but all of the asteriod pieces still entered the earth's atmosphere, then you're going to end up releasing pretty much an identical amount of energy. At "city buster" size of impact, this would probably be beneficial. But beyond that? Probably not hugely beneficial. Probably effectively the difference between a ground detonation and a partial airburst.. so maybe less ejecta (reduced global dimming after). But... probably not a meaningful change.
  - burnte 3y ago
    Yes the energy is identical, but the volume across with the energy is dispersed is the benefit. Even if you "only" break up an asteroid so that the rubble falls all over the world across a few days or weeks, that's nothing compared to the asteroid in one piece hitting. It's not the fall, it's the sudden stop at the end. Make that fall over days/weeks and a million times the area, you're fine.
    - mcbutterbunz 3y ago
      Still depends on the amount of energy being released. Burning up a large enough asteroid would cook the planet, even at days/weeks/months. I guess it really depends on the rate at which heat is lost to space.
    - LorenPechtel 3y ago
      It's all going to fall at basically the same instant. At small rocks destroying them is a good thing. At big rocks destroying them is worse than not shooting: Blast radius goes at the cube root of energy, blast area goes at the square of blast radius. Thus if you were to break an incoming rock into 8 equal parts the blast radius of each impact would be halved, the blast area quartered--but there would be 8 hits, for a final result of doubling the blast area. The smaller the pieces the worse the effect until you get down to the point where they burn rather than hit. (And that brings it's own problems with flash heating.) Thus big rocks must only be deflected, not destroyed.
      - EthanHeilman 3y ago
        All of this depends on the actual parameters we are talking about > last radius goes at the cube root of energy, blast area goes at the square of blast radius. Only up to the point at which the blast wave touches atmosphere then strange things happen because the blast is now being tunneled into a vacuum. This likely reduces the blast of very big asteroids by channeling most of the energy back into space. However blast area isn't the only concern. An ice age can be triggered if enough matter is blasted into the upper atmosphere. You might increase the blast area by breaking the asteroid into smaller pieces but completely eliminate the risk of depositing light blocking particles in the upper atmosphere. It is by no means guaranteed that if you break a big asteroid into eight pieces, they will all hit. The energy to split an asteroid may confer sufficient momentum that small if not all the pieces miss the Earth.
- simonh 3y ago
  Dangerous asteroid sizes span many orders of magnitude from the smallest real global danger to the largest. Breaking one up would work for asteroids over maybe tgevlowest order of magnitude size range, but that still leaves many more orders of magnitude in larger sizes for which it wouldn’t help you much.
- lamontcg 3y ago
  Meteors smaller than 25m burn up in the Earth's atmosphere: https://www.nasa.gov/mission_pages/asteroids/overview/fastfacts.html https://www.nasa.gov/mission_pages/asteroids/overview/fastfa...

sproketboy 3y ago

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RosanaAnaDana 3y ago

Wouldn't breaking up a planetary defense worthy asteroid into medium to even large boulder size asteroids be considered a win? Whats the limit on asteroid size that can make it through the atmosphere? And even then, intuitively, it would seem like the destructiveness is going to scale with the size of the individual asteroid, so a rain of many smaller asteroids making it to ground would be far lower than one large asteroid..

icegreentea2 3y ago
It depends on what the threshold for 'planetary defense worthy' is I guess. If you shattered an asteroid, but all of the asteriod pieces still entered the earth's atmosphere, then you're going to end up releasing pretty much an identical amount of energy. At "city buster" size of impact, this would probably be beneficial. But beyond that? Probably not hugely beneficial. Probably effectively the difference between a ground detonation and a partial airburst.. so maybe less ejecta (reduced global dimming after). But... probably not a meaningful change.
- burnte 3y ago
  Yes the energy is identical, but the volume across with the energy is dispersed is the benefit. Even if you "only" break up an asteroid so that the rubble falls all over the world across a few days or weeks, that's nothing compared to the asteroid in one piece hitting. It's not the fall, it's the sudden stop at the end. Make that fall over days/weeks and a million times the area, you're fine.
  - mcbutterbunz 3y ago
    Still depends on the amount of energy being released. Burning up a large enough asteroid would cook the planet, even at days/weeks/months. I guess it really depends on the rate at which heat is lost to space.
  - LorenPechtel 3y ago
    It's all going to fall at basically the same instant. At small rocks destroying them is a good thing. At big rocks destroying them is worse than not shooting: Blast radius goes at the cube root of energy, blast area goes at the square of blast radius. Thus if you were to break an incoming rock into 8 equal parts the blast radius of each impact would be halved, the blast area quartered--but there would be 8 hits, for a final result of doubling the blast area. The smaller the pieces the worse the effect until you get down to the point where they burn rather than hit. (And that brings it's own problems with flash heating.) Thus big rocks must only be deflected, not destroyed.
    - EthanHeilman 3y ago
      All of this depends on the actual parameters we are talking about > last radius goes at the cube root of energy, blast area goes at the square of blast radius. Only up to the point at which the blast wave touches atmosphere then strange things happen because the blast is now being tunneled into a vacuum. This likely reduces the blast of very big asteroids by channeling most of the energy back into space. However blast area isn't the only concern. An ice age can be triggered if enough matter is blasted into the upper atmosphere. You might increase the blast area by breaking the asteroid into smaller pieces but completely eliminate the risk of depositing light blocking particles in the upper atmosphere. It is by no means guaranteed that if you break a big asteroid into eight pieces, they will all hit. The energy to split an asteroid may confer sufficient momentum that small if not all the pieces miss the Earth.
simonh 3y ago
Dangerous asteroid sizes span many orders of magnitude from the smallest real global danger to the largest. Breaking one up would work for asteroids over maybe tgevlowest order of magnitude size range, but that still leaves many more orders of magnitude in larger sizes for which it wouldn’t help you much.
lamontcg 3y ago
Meteors smaller than 25m burn up in the Earth's atmosphere: https://www.nasa.gov/mission_pages/asteroids/overview/fastfacts.html https://www.nasa.gov/mission_pages/asteroids/overview/fastfa...