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 how disastrous would this be?

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silviour

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PostSubject: how disastrous would this be?    Wed Aug 24, 2011 11:06 am

An object weighing 50k metric tons travelling at 12% of c slams into an object somewhere between the size of Mars and Earth.

If it's a Jovian (say 1-3 jupiter masses) would it seriously affect it and maybe come through the other side or just leave a big black scar like Shoemaker-Levy 9 on PCP?
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astrolover

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PostSubject: Re: how disastrous would this be?    Wed Aug 24, 2011 11:08 am

What is PCP? 50,000 metric tons is about 8000 cubic meters = a cube 20 meters on an edge or a sphere with a diameter of about 23 meters. At one thousandth c, that size would do little or no damage after passing though the atmosphere. 12% of c is much faster than is probable, but 12% would do damage equal to 5 megaton H bomb. 5 megaton would do negligible damage to a 1 to 3 Jupiter gas giant planet. The scar would disappear in a few weeks.
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scopeman

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PostSubject: Re: how disastrous would this be?    Wed Aug 24, 2011 11:44 am

I'm not an expert on this kind of thing, but there're several factors we can consider. Firstly the Kinetic Energy of the object. A 50,000,000 kg object travelling at 36,000,000 m/s (12% speed of light) will have a (Relativistic) kinetic energy of 3.2755x10^22 joules of energy (According to the Relativistic kinetic energy Calculator on this Website: hyperphysics - Relativistic Energy ). That's equivalent to 7.83 Teratons of TNT (or about 8 million Megatons), which is far, far more than all the world's nuclear arsenals combined.

Now as for effects of this on a planet, well there is this nice little calculator program here: The Earth Impact Effects Program. This program was designed to simulate asteroid impacts, but I think it can be made to work for relativistic objects to. If we assume the object is made out of Iron and has a density of 8,000 kg/m^3, then it will be a sphere 22.854 metres in diameter. Putting this into the calculator with a "perfect" impact angle of 90 degrees, the results say that the object would begin to burn up in the Earth's upper atmosphere and would then explode in an Air Burst about 7.5 km from the surface. This would be an incredibly destructive explosion and would surely destroy all buildings and kill anyone within several hundred kilometres and would do significant damage out to thousands of kilometres.

It is also predicted that the object would break apart into many large pieces during the explosion and these would likely impact the surface causing potentially major explosions and craters of their own. This could kick up large amounts of dust into the atmosphere maybe causing a drop in global temperatures (the so called "nuclear winter", although I don't know how severe it would be).

All in all, it would totally devastate whatever part of the Earth was hit and might have knock-on effects to the rest of the world. There is another potential effect that could be very bad as well though, that's the heating effect on the Atmosphere. I don't know how to calculate this exactly, but I've hear that major impacts can cause a kind of world-wide fireball effect (massive heating of the atmosphere, causing things to spontaneously ignite), though I don't know how big an explosion would have to be to cause this. The only thing I can look to is this Nuclear Weapon Effects Calculator, if we put in the predicted energy of the air blast of 5.6 teratons, it says there would be a "Thermal radiation" effect causing "3rd degree burns" to any exposed people out to 6,800 km. Now if we assume this is accurate and that such an impact will act similarly to a nuclear explosion, then we can say that the light and heat flash would be seen and felt across nearly half the Earth.

This of course all assumes that it hits the Earth, if it hits a planet without an atmosphere, then it will simply impact directly on the surface causing one huge explosion and crater. There are ways to calculate crater size, etc, I don't know how to do that (maybe someone else here does). If it hits a gas giant I am certain it would burn up and explode in the upper atmosphere, similarly to how it does in Earth's. It wouldn't really do any damage to the planet (can you damage a gas giant?), but I think the explosion would definitely be visible from outside like a cometary impact, perhaps a large shockwave would move out across the planet. It would certainly not go through the planet though.
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Clive_D



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PostSubject: Re: how disastrous would this be?    Wed Aug 24, 2011 11:44 am

astrolover wrote:
What is PCP? 50,000 metric tons is about 8000 cubic meters = a cube 20 meters on an edge or a sphere with a diameter of about 23 meters. At one thousandth c, that size would do little or no damage after passing though the atmosphere. 12% of c is much faster than is probable, but 12% would do damage equal to 5 megaton H bomb. 5 megaton would do negligible damage to a 1 to 3 Jupiter gas giant planet. The scar would disappear in a few weeks.

At 300kps the KE would be 25x10^6x9x10^10=2.25x10^18 J or 537 megatonnes

At .12c the KE would be 25x10^6x(36x10^6)^2=3.24x10^22 J or 7 million megatonnes (without correcting for SR)

If it were rock or harder, the .1%c rock would blow up a state. At 12%c, you would blow up a continent.

Niether would do much to a gas giant tho.
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scopeman

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PostSubject: Re: how disastrous would this be?    Wed Aug 24, 2011 11:46 am

astrolover wrote:
What is PCP?

Phenylcyclohexylpiperidine. Commonly contracted to phencyclidine, with the street name angel dust. A once-fashionable recreational hullucinogen, which caused a bit of a moral panic in the 70s and 80s because of its reported association with mania, paranoia and aggression. I'm guessing the last-mentioned effect is what's being referred to in the OP.
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andy 'astrojunkie'
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PostSubject: Re: how disastrous would this be?    Wed Aug 24, 2011 11:46 am

WOW not an expert lol...

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