Large astroid hitting earth

[DrPizza]

Originally posted by: Vee

Originally posted by: egkenny
Impact of 15 km wide meteor or comet with Earth = upwards of 100 megatons of TNT

There's got to be something wrong here.

A comet that is in elliptical orbit around the sun can reach us with an impact velocity of 50km/s. A parabolic comet would come at any, higher, speed.

So the impact energy from 15km wide objects should be more like
upwards of 100 million * million * megatons. You seem to have lost a factor of 10^12 somewhere?


Edit: removed assumption that near Earth objects in examples came from the asteroid belt.

Agreed... something's off on the 15km comet. Only 100 Megatons?! I'd expect that a 15km comet would be considered an extinction or near-extinction event.

Did a bit of googling: Here, from Wikipedia:

Based on crater formation rates determined from the Earth's closest celestial partner, the Moon, astrogeologists have determined that during the last 600 million years, the Earth has been struck by 60 objects of a diameter of five kilometers or more. The smallest of these impactors would release the equivalent of 10 million megatons of TNT and leave a crater 95 kilometers across. For comparison, the largest nuclear weapon ever detonated, the Tsar Bomba, had a yield of 50 megatons.

wiki entry

To compare, estimates I found for the Tunguska event (Siberia, 1908, most likely a comet that exploded in the upper atmosphere, leveled 2150 square kilometers, estimated 10-15 megatons) was about a 60 meters in diameter.
Simply from 4/3 pi r^3, r=30meters vs. radius = 7500meters (for your 15km comet), a 15km comet would be 250^3 times larger or roughly 15 million times as massive. Since ke = .5mv^2, there would be 15 million times more energy. (assuming a uniform density between the two) or, 150 to 225 million megatons, which agrees with the approximation of the energy released by the (whatever it was called) event 65 million years ago when the Yucatan was struck (estimated at 10-15km)

I think you just inadvertently left out the "million" in front of megatons, and didn't pick it up in Vee's post either.

 

[egkenny]

Originally posted by: DrPizza

Originally posted by: Vee

Originally posted by: egkenny
Impact of 15 km wide meteor or comet with Earth = upwards of 100 megatons of TNT

There's got to be something wrong here.

A comet that is in elliptical orbit around the sun can reach us with an impact velocity of 50km/s. A parabolic comet would come at any, higher, speed.

So the impact energy from 15km wide objects should be more like
upwards of 100 million * million * megatons. You seem to have lost a factor of 10^12 somewhere?


Edit: removed assumption that near Earth objects in examples came from the asteroid belt.

Agreed... something's off on the 15km comet. Only 100 Megatons?! I'd expect that a 15km comet would be considered an extinction or near-extinction event.

Did a bit of googling: Here, from Wikipedia:

Based on crater formation rates determined from the Earth's closest celestial partner, the Moon, astrogeologists have determined that during the last 600 million years, the Earth has been struck by 60 objects of a diameter of five kilometers or more. The smallest of these impactors would release the equivalent of 10 million megatons of TNT and leave a crater 95 kilometers across. For comparison, the largest nuclear weapon ever detonated, the Tsar Bomba, had a yield of 50 megatons.

wiki entry

To compare, estimates I found for the Tunguska event (Siberia, 1908, most likely a comet that exploded in the upper atmosphere, leveled 2150 square kilometers, estimated 10-15 megatons) was about a 60 meters in diameter.
Simply from 4/3 pi r^3, r=30meters vs. radius = 7500meters (for your 15km comet), a 15km comet would be 250^3 times larger or roughly 15 million times as massive. Since ke = .5mv^2, there would be 15 million times more energy. (assuming a uniform density between the two) or, 150 to 225 million megatons, which agrees with the approximation of the energy released by the (whatever it was called) event 65 million years ago when the Yucatan was struck (estimated at 10-15km)

I think you just inadvertently left out the "million" in front of megatons, and didn't pick it up in Vee's post either.

You're right. I looked back at my original source and verified that I left out "million". I fixed the original quote.

If you do the math and use a density of 2.6 g/cm3 for a 15 km diameter asteroid traveling at 13 km/s you will get about 93 million megatons of TNT for the impact energy.

Of course this all guesswork. All we have are the remains of a crater estimated to be millions of years old. We can only guess at the size of the asteroid, its diameter, its mass, its velocity, and its angle of descent into the atmosphere.

 

[Future Shock]

Originally posted by: Soccerman06

Originally posted by: Dimicron

Originally posted by: Soccerman06
No not really, Its quite easy to get a delivery system that far, we already have technology to get that far like ion drives and solar sails. Do a little research before you post egkenny

...and how many probes have been lost heading to Mars?

I said nothing about the payload reaching the rock, just said its easy to get out that far.

I love your definition of easy...even taking an off-the-shelf booster, with a waited-for launch (miniumum energy) window, it takes hundreds of people working for years to make it happen - and still fails nearly as often as it succeeds.

How this relates statistically to building a new, 3 orders-of-magnitude larger booster, with no chance of building and firing prototypes, firing from an immediate launch window, from a launch platform that isn't even built yet (something the size of say Puerto Rico would be needed to be safe)...

The first isn't easy by my definition, and the second would be merely one step more believable than magic.

N.B. - we can't even build a newer version of the old Saturn 5, still the most mighty launcher ever designed. Someone at NASA (I kid you not) threw all the plans away during a "spring cleaning" excercize...we can't even get a decent sized payload to the Moon right now...

Future Shock

 

[the splat in the hat]

bout as easy as going to mars at this piont !

 

[egkenny]

Originally posted by: the splat in the hat
bout as easy as going to mars at this piont !

Going to Mars is actually easier because you can use a low energy trajectory. You are much more time constrained when you have a speeding asteroid coming at you. You have to get to it before it is too late to do anything.

 

[Armitage]

ESA attempt to deflect an asteroid: http://www.esa.int/esaCP/SEML9B8X9DE_index_0.html

 

[Travis Keller]

Large dense rocks travling at high speeds can do damage!!!!!!!!!!!!!!