5 ms·

15kms at 80km/s So, for a quarter of a second or less it was touching the ground and almost double the height of Everest (8.8kms).

by jvm___ 3y ago

Cthulhu_ 3y ago
I wonder if just the atmosphere would've caused it to explode already. At those speeds it'd go through the atmosphere within a second though.
- Filligree 3y ago
  It would be exploding for the duration, but at that size you just can’t get through much of the asteroid before it touches the ground.
- dylan604 3y ago
  That's why "dense rock" setting was used. Imagine if they had selected "solid iron". I don't know what settings are available for the calculator used, but "loose bunch of rocks" would probably fall apart in the atmo, dense rock would hold together until impact, and solid iron would just keep burrowing further
  - kijin 3y ago
    A 15km chunk of solid iron, now that's the kind of bunker buster you throw around in an interplanetary war. Would it do more damage to the surface than a rocky asteriod of comparable mass, though? If it burrows deeper, it means it transfers more of its energy to the mantle and core of the Earth, and less to the crust. It will be like a full metal jacket bullet that goes straight through the target and transfers most of its energy to the wall on the other side, versus a regular bullet that tumbles and expands as soon as it hits the target.
    - davidwritesbugs 3y ago
      Throwing Meteors as interplanetary weapons was a storyline from The Expanse books/TV series if I recall.
      - jvm___ 3y ago
        Deorbiting a multi-million dollar satellite as a weapon was the plot of of a Tom Clancy book. The bad guy was going to launch a nuke from his ship and the only thing that could get there in time was the super special satellite.
        dylan604 3y ago
        Was this an OpCenter plot? It's definitely not a Jack Ryan series plot. I never really picked up the post-divorce stuff he wrote.
      - mekkkkkk 3y ago
        Yeah. Bad guy mounted thrusters on large asteroids from the belts. Not technically meteors, but close enough. Neat sci-fi.
    - mr_toad 3y ago
      At that speed I’m pretty sure that it would be vaporised on impact, so it wouldn’t matter.
- RetroTechie 3y ago
  For such a size impactor, atmosphere does nothing. Might as well be vacuum. Sure, milliseconds before impact the atmosphere might be super-compressed (and super-heated). Perhaps even exert considerable force. But compared with kinetic energy of that size impactor, at such speed: negligable. Small objects 'feel' the atmosphere much stronger. Surface area vs. volume.
  - jacquesm 3y ago
    Whatever parts of the atmosphere were involved in the direct vicinity of the impactor would be heated to plasma. It is just too much energy, you're talking about the equivalent of a massive number of H-Bombs all going off at roughly the same time.
    - jvm___ 3y ago
      It would probably punch a 15km wide hole in the atmosphere, no? Which would then rapidly collapse from the sides and collide with whatever was ejected... would be fun to watch while parked somewhere safe in orbit.
      - jacquesm 3y ago
        Better not be LEO... I wonder how high the ejecta would go and how far they would reach across the planet.
      - two_in_one 3y ago
        15 km diameter is about the size of "thick" atmosphere. The mass of the air in this volume is something about 0.000..% . At speed of 80 km/sec, well, atmosphere didn't slow it down much. And if there was only microbial life at that time it adapted and bounced back quickly.
        jvm___ 3y ago
        I was thinking of it's 80km/s wake through the atmosphere. Coming straight in it wouldn't be long horizontally but the clap of 15kms of atmosphere being pushed aside and then coming together behind it...
- pmayrgundter 3y ago
  Got me thinking, What happens, when and where. A column of air weighs ~1kg/cm^2 (handy!), and the example has a 15km span of "Dense Rock" which I've seen mean "Dense Rock Equivalent" in the Volcanic Explosivity Index, where it has a density of 2,500 kg/m^3. Assuming that, a column of the asteroid is 2500kg/cm^2/(100cm/m * 100cm/m) = .25kg/m * 15km = 3,750kg The kinetic energy per column of the impactor is 1/2mv^2, or 0.5 * 3750 * 80000m/s^2, or 1875 * 6.4e9m^2/s^2 = 1.2e13 Joules Which is about 20 gallons of gasoline equivalent. As you say, that's absorbed in ~1s (space is 100km up, so 80km/s is just about right). If so that warms up and starts melting the surface of the asteroid, but not much more I guess.
  - pmayrgundter 3y ago
    Whoops, I carried down the wrong number to the gasoline conversion.. I left off the 1875 The whole impact is like 40000 gallons of gasoline per cm^2 of surface, or I think like 2kt TNT. So then, not sure what the kinetics/kinematics is there. How much is released by the atmosphere impact vs then the surface stopping the asteroid.
    - pmayrgundter 3y ago
      Ok! ChatG4 is amazing! https://chat.openai.com/share/25e4cef6-321a-43f7-8d13-40d1fd1a81bc https://chat.openai.com/share/25e4cef6-321a-43f7-8d13-40d1fd... Summary: my initial math checks out for the total KE of the asteroid, and then we used that to look at the surface heating by the compressed atmosphere and then the Fourier heat analysis of conduction into the asteroid surface Answer: Tho the atmosphere would be heated to 100k degrees and that's 1000x more than needed for vaporization of e.g. granite, the duration of ~1s means that only a few millimeters of surface would be vaporized by the time of impact.
      - serf 3y ago
        does it give the same answer repeatedly? every time i've tried to solve problems like that with chatgpt i've been given beautifully worded garbage that doesn't commpute by hand, and won't be repeated if I retry the prompt.
- jacquesm 3y ago
  Much too large for that. Under 50 meters or so you can get airbursts, after that it is direct impact.
tomatotomato37 3y ago
It makes me wonder what an impactor like that would do if intercepted by the moon; that may be even enough mass to cause a temporary ring field just from the debris
- _whiteCaps_ 3y ago
  If you wonder about things like that, you might want to read Seveneves by Neal Stephenson.
jacquesm 3y ago
And it still only went down to about twice its diameter. Makes you really respect how tough the Earth's crust is.
- jvm___ 3y ago
  The deepest borehole, about the size of a coffee can, is only 12km deep before the tooling started melting - can't drill with a liquid bit... So 30km down it would be hitting liquid rock and a lot of heat.
  - jacquesm 3y ago
    Yes, the mantle is about that thick. And much thinner in some places even. Which makes me wonder how they detected this crater and what the crater is formed in. This is the relevant bit from the article: "Between 1995 and 2000, Tony Yeates suggested magnetic patterns beneath the Murray Basin in New South Wales likely represented a massive, buried impact structure. An analysis of the region’s updated geophysical data between 2015 and 2020 confirmed the existence of a 520km diameter structure with a seismically defined dome at its centre. The Deniliquin structure has all the features that would be expected from a large-scale impact structure. For instance, magnetic readings of the area reveal a symmetrical rippling pattern in the crust around the structure’s core. This was likely produced during the impact as extremely high temperatures created intense magnetic forces." But they would not able to verify that at that depth without a lot of drilling and the end of the article suggests that they have yet to do so.

15kms at 80km/s So, for a quarter of a second or less it was touching the ground and almost double the height of Everest (8.8kms).

by jvm___ 3y ago

15kms at 80km/s So, for a quarter of a second or less it was touching the ground and almost double the height of Everest (8.8kms).

Cthulhu_ 3y ago

I wonder if just the atmosphere would've caused it to explode already. At those speeds it'd go through the atmosphere within a second though.

Filligree 3y ago
It would be exploding for the duration, but at that size you just can’t get through much of the asteroid before it touches the ground.
dylan604 3y ago
That's why "dense rock" setting was used. Imagine if they had selected "solid iron". I don't know what settings are available for the calculator used, but "loose bunch of rocks" would probably fall apart in the atmo, dense rock would hold together until impact, and solid iron would just keep burrowing further
- kijin 3y ago
  A 15km chunk of solid iron, now that's the kind of bunker buster you throw around in an interplanetary war. Would it do more damage to the surface than a rocky asteriod of comparable mass, though? If it burrows deeper, it means it transfers more of its energy to the mantle and core of the Earth, and less to the crust. It will be like a full metal jacket bullet that goes straight through the target and transfers most of its energy to the wall on the other side, versus a regular bullet that tumbles and expands as soon as it hits the target.
  - davidwritesbugs 3y ago
    Throwing Meteors as interplanetary weapons was a storyline from The Expanse books/TV series if I recall.
    - jvm___ 3y ago
      Deorbiting a multi-million dollar satellite as a weapon was the plot of of a Tom Clancy book. The bad guy was going to launch a nuke from his ship and the only thing that could get there in time was the super special satellite.
      - dylan604 3y ago
        Was this an OpCenter plot? It's definitely not a Jack Ryan series plot. I never really picked up the post-divorce stuff he wrote.
    - mekkkkkk 3y ago
      Yeah. Bad guy mounted thrusters on large asteroids from the belts. Not technically meteors, but close enough. Neat sci-fi.
  - mr_toad 3y ago
    At that speed I’m pretty sure that it would be vaporised on impact, so it wouldn’t matter.
RetroTechie 3y ago
For such a size impactor, atmosphere does nothing. Might as well be vacuum. Sure, milliseconds before impact the atmosphere might be super-compressed (and super-heated). Perhaps even exert considerable force. But compared with kinetic energy of that size impactor, at such speed: negligable. Small objects 'feel' the atmosphere much stronger. Surface area vs. volume.
- jacquesm 3y ago
  Whatever parts of the atmosphere were involved in the direct vicinity of the impactor would be heated to plasma. It is just too much energy, you're talking about the equivalent of a massive number of H-Bombs all going off at roughly the same time.
  - jvm___ 3y ago
    It would probably punch a 15km wide hole in the atmosphere, no? Which would then rapidly collapse from the sides and collide with whatever was ejected... would be fun to watch while parked somewhere safe in orbit.
    - jacquesm 3y ago
      Better not be LEO... I wonder how high the ejecta would go and how far they would reach across the planet.
    - two_in_one 3y ago
      15 km diameter is about the size of "thick" atmosphere. The mass of the air in this volume is something about 0.000..% . At speed of 80 km/sec, well, atmosphere didn't slow it down much. And if there was only microbial life at that time it adapted and bounced back quickly.
      - jvm___ 3y ago
        I was thinking of it's 80km/s wake through the atmosphere. Coming straight in it wouldn't be long horizontally but the clap of 15kms of atmosphere being pushed aside and then coming together behind it...
pmayrgundter 3y ago
Got me thinking, What happens, when and where. A column of air weighs ~1kg/cm^2 (handy!), and the example has a 15km span of "Dense Rock" which I've seen mean "Dense Rock Equivalent" in the Volcanic Explosivity Index, where it has a density of 2,500 kg/m^3. Assuming that, a column of the asteroid is 2500kg/cm^2/(100cm/m * 100cm/m) = .25kg/m * 15km = 3,750kg The kinetic energy per column of the impactor is 1/2mv^2, or 0.5 * 3750 * 80000m/s^2, or 1875 * 6.4e9m^2/s^2 = 1.2e13 Joules Which is about 20 gallons of gasoline equivalent. As you say, that's absorbed in ~1s (space is 100km up, so 80km/s is just about right). If so that warms up and starts melting the surface of the asteroid, but not much more I guess.
- pmayrgundter 3y ago
  Whoops, I carried down the wrong number to the gasoline conversion.. I left off the 1875 The whole impact is like 40000 gallons of gasoline per cm^2 of surface, or I think like 2kt TNT. So then, not sure what the kinetics/kinematics is there. How much is released by the atmosphere impact vs then the surface stopping the asteroid.
  - pmayrgundter 3y ago
    Ok! ChatG4 is amazing! https://chat.openai.com/share/25e4cef6-321a-43f7-8d13-40d1fd1a81bc https://chat.openai.com/share/25e4cef6-321a-43f7-8d13-40d1fd... Summary: my initial math checks out for the total KE of the asteroid, and then we used that to look at the surface heating by the compressed atmosphere and then the Fourier heat analysis of conduction into the asteroid surface Answer: Tho the atmosphere would be heated to 100k degrees and that's 1000x more than needed for vaporization of e.g. granite, the duration of ~1s means that only a few millimeters of surface would be vaporized by the time of impact.
    - serf 3y ago
      does it give the same answer repeatedly? every time i've tried to solve problems like that with chatgpt i've been given beautifully worded garbage that doesn't commpute by hand, and won't be repeated if I retry the prompt.
jacquesm 3y ago
Much too large for that. Under 50 meters or so you can get airbursts, after that it is direct impact.

tomatotomato37 3y ago

It makes me wonder what an impactor like that would do if intercepted by the moon; that may be even enough mass to cause a temporary ring field just from the debris

_whiteCaps_ 3y ago
If you wonder about things like that, you might want to read Seveneves by Neal Stephenson.

jacquesm 3y ago

And it still only went down to about twice its diameter. Makes you really respect how tough the Earth's crust is.

jvm___ 3y ago
The deepest borehole, about the size of a coffee can, is only 12km deep before the tooling started melting - can't drill with a liquid bit... So 30km down it would be hitting liquid rock and a lot of heat.
- jacquesm 3y ago
  Yes, the mantle is about that thick. And much thinner in some places even. Which makes me wonder how they detected this crater and what the crater is formed in. This is the relevant bit from the article: "Between 1995 and 2000, Tony Yeates suggested magnetic patterns beneath the Murray Basin in New South Wales likely represented a massive, buried impact structure. An analysis of the region’s updated geophysical data between 2015 and 2020 confirmed the existence of a 520km diameter structure with a seismically defined dome at its centre. The Deniliquin structure has all the features that would be expected from a large-scale impact structure. For instance, magnetic readings of the area reveal a symmetrical rippling pattern in the crust around the structure’s core. This was likely produced during the impact as extremely high temperatures created intense magnetic forces." But they would not able to verify that at that depth without a lot of drilling and the end of the article suggests that they have yet to do so.