Quote:
|
Originally Posted by tellumFS
So the material has nothing to do with it? Say a 1km square rock vs. a 1km square ice hunk. Would the ice hunk burn up more, or at that size, does it matter anymore?
|
I don't know if this helps, but it is some neat information. =)
At that size, energy goes from the orbital thingy to the earth.
1 km square ice hunk weighs about 1 billion tonnes. Solar escape velocity is about 43 kilometers a second. Assuming that comets impact the earth at about solar escape velocity seems reasonable. (The Earth orbits the sun at about 30 km/sec. Comets hitting the Earth would be moving faster than the Earth. Their sum coming to solar escape velocity seems reasonable.)
E = 1/2 m v^2
E =~ 1.9 * 10^18 kg m^2/s^2
This is roughly the same amount of energy in the earthquake that triggered the Indian ocean tsunami. Or, the same energy as about 1000 hydrogen bombs (1 H-bomb could wipe out greater NYC -- every building flattened). The tsunami only contained the energy from about 5 megatonnes of TNT (5 H-bombs) -- the tsunami was a secondary effect.
The earthquake, however, was mainly about shaking large chunks of ground and moving rock around. A comet would instead vapourize water and rock where it hit, sending large quantities of dust into the atmosphere, and a plasma plume into space that would land on the far side of the world.
How much would the comet slow down?
The amount of mass in a column of air 1 km square, to the edge of the atmosphere, is 100 KPa * 1 km^2 / 9.8 m/s^2 =~ 10^10 kg. This is 100 times lighter than your 1 km cube of ice: I doubt it would get in the way much. The comet is coming in supersonically, so all that air would build up under the incoming body without having time to move sideways much. It only takes the comet a second to go from the ozone layer to the surface of the Earth, and shockwaves don't move that quickly through air.
Take a car, and ram it into something weighing 100 times less than the car. The car doesn't even slow down noticeably -- I suspect the same would happen to the 1 km^3 comet.
A rock comet coming down would have 2 to 4 times the density of the ice cube, which means 2 to 4 times the mass. This would make the air even more trivial, and make the impact that much more impressive.