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0 pointsbuildbot2y ago0 comments

A relativistic asteroid would not be a good time for earth. Apparently according to gpt4 (so big grain of salt), a 1km asteroid going 0.9c is roughly 4.37×10^16 megatons of TNT worth of energy.

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7 comments · 4 top-level

dylan6042y ago· 2 in thread

that's one of those too big to comprehend type numbers. that's fine when talking about number of atoms, or the distances to another galaxy. trying to have my brain apply that to explosion just immediately goes to BSOD

buildbotOP2y ago

Yeah same haha - for a slightly more relevant number, if every nuclear weapon yielded 50MT of TNT, the asteroid impact is approx 63 Billion times the entire worlds nuclear arsenal in terms of power.

short_sells_poo2y ago

And that is still impossible to comprehend, so how about this, the Sun's energy output is about 10^10 megatons of tnt per second, so this impact would release 1 million second's worth of the Sun's output, or about 12 days. In other words, it would instantly vaporize the entire planet.

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pineaux2y ago· 1 in thread

This is in the correct ballpark. But 0.9c is crazy fast. [Expanse spoiler alert]

I love how they use this mechanic for storytelling in "The Expanse". The rebels of the belt threaten earth by slinging rocks at it at really high speed. Seems a very realistic way of interplanetary war. Why not bend some fast moving rocks to your enemy?

aurelwu2y ago

I don't know if it's been the first time in fiction where that concept was described but in Heinleins "The Moon is a harsh Mistress" this was what the Moon Colonists did.

Terr_2y ago

> according to gpt4 (so big grain of salt) [...] 4.37×10^16 megatons

I decided to challenge the glorified-autocorrect machine with some more-manual napkin math, and I get 5.56×10^13 megatons, which is smaller by a factor of ~786x.

That discrepancy is too big to explain just in terms of asteroid composition: Even an impactor of pure Osmium would only be ~12x more energetic.

Here's my work, if anyone wants to check for errors:

    Asteroid volume                        1    km³ 
    Asteroid density 1                     2    grams / cm³ https://en.wikipedia.org/wiki/Standard_asteroid_physical_characteristics
    Volume conversion                  1E+15    cm³ / km³   
    Asteroid density 2                 2E+15    grams / km3 
    Asteroid mass                      2E+15    grams   
    Asteroid velocity                    0.9    c   
    Relativistic kinetic energy     2.33E+29    joules      https://www.omnicalculator.com/physics/relativistic-ke
    TNT energy                      4.18E+03    joules/gram 
    TNT mass equivalent 1           5.56E+25    grams   
    Mass conversion                 1.00E+12    grams per megaton   
    TNT mass equivalent 2           5.56E+13    megatons

szundi2y ago

Or a grain of TNT

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