[lelio]

striking with the energy of 100 million megatons of TNT

Where on earth did he get this figure from? The Hiroshima and Nagasaki bombs were in the 12-20 KILO ton range, meaning this explosion is 5 MILLION times stronger (provided that a megaton = 1000 kilotons).

[LibWhacker]

I think it's just based on the physics of the situation; e.g., what is the kinetic energy of Mt. Everest approaching Earth at ~30 miles/sec?

[Junior]

One of the clues is the size of the crater, which is still extant.

[Drammach]

Where on earth did he get this figure from?

The first Hydrogen (Fusion) bomb was approx 10.4 Megatons.
It left a crater a mile wide..

The biggest H-bomb ever tested by the U.S. was 15 Megatons.
It left a crater 250 ft. deep and 6250 ft wide..

What's the size of the Yucatan Crater?
I would guess about 10 miles wide, and somewhere around 2000 to 2200 ft deep..

i.e., 100 megatons..

The Russians had designs for 100 megaton H-bombs, but never actually tested any.. ( not sure if they ever built one or not )

[Drammach]

Here's a link to an interesting article..

http://www.space.com/scienceastronomy/planetearth/asteroid_jello_001122.html

Says the crater is 100 - 150 miles wide..

I would have to revise my estimate another power of 10....

1,000 megatons.. or .. 1 to 1.5 GIGATONS..

[Kozak]

Where on earth did he get this figure from? The Hiroshima and Nagasaki bombs were in the 12-20 KILO ton range, meaning this explosion is 5 MILLION times stronger (provided that a megaton = 1000 kilotons).

an asteroid with a 6 mile diameter would be about 110 cubic MILES of rock and iron hitting the earth at speeds of up to 50,000 miles an hour. Thats a hell of a lot of KE. Comet Shumaker Levy smacked Jupiter hard enough to leave earth sized holes in the cloud cover that lasted weeks. This has happened and will happen again.

[Centurion2000]

Meteor impact table

You might like this link. It uses kinetic energy calculations to determine approximate energy yields for various impacting bodies.

[AFPhys]

Though it appears at first that these energies are hard to imagine, it is very straightforward to do the calculations.
I don't have time to rebuild the calculations I've done several times in the past now, though.

Simply assume a mass 0.5-10 miles (1000-16000 meters) on a side and with a density about 3-5 times that of water for rock, 1-1.5 times water (which is 1000 kilograms/ cubic meter) for a water laden comet. It doesn't matter that much. It is easier to assume the mass is cubic instead of roundish, and again it doesn't matter much.

The huge energy factor is the velocity, which ranges from 20,000-80,000 mph (10-40 kilometers/ sec) for most comets/meteors/asteroids when they strike the earth's atmosphere.

For ease of your calculations, I provide that a single megaton of energy is equal to 4,186,000,000,000 joules (4.186 X 10^12) of energy (1,000,000,000 kilogram-meter^2/ sec^2) ... and I suggest you convert the masses and dimensions for your impact body to metric.

You will find that a moderate size asteroid striking the earth deposits many, many times the energy of the full arsenal of nuclear bombs on earth. Even the small 1ft diameter rocks end their life as spectacular fireballs seen noted for hundreds of miles. Fortunately, we don't get hit by anything bigger than a ten or twenty yards in diameter very often, but even those result in things like Crater Lake.