Wednesday, November 17, 2010

Have Fun Crashing Asteroids Into The Earth

We used Purdue University's "Impact: Earth!" program to run various asteroid crash scenarios, to see what would happen if an object crashed into the Earth near Brooklyn.

This fun simulation lets you vary your inputs: size of asteroid, density of asteroid, degree of impact, speed of flight, distance (you are) from impact and what the asteroid crashes into.

We soon learned that a small asteroid -- say, 2 feet across -- wouldn't be especially exciting unless it hit you on the head. As it gets bigger, denser and faster, the effects become correspondlingly more dramatic.

We wanted to produce a tsunami, so we did a bit of research and found that there are trench-like depressions about a hundred miles from Sandy Hook, N.J., south of Brooklyn, where the water obtains the depth of 2,700 feet. This is very roughly 115 miles from Downtown Brooklyn. (Area circled below shows the trench in the ocean floor, courtesy of Google Maps. You can click on it to see it better.)

What Would Happen
 We decided to simulate what would happen if the Earth were hit by the Apophis Asteroid, which is supposed to pass close to the Earth sometime this century.

When we plugged in a dense rock the size of Apophis -- 270 meters (885 feet) across -- hitting the water at the trench at a 45 degree angle, traveling 72 km/sec., the program computed the effects we would feel in Downtown Brooklyn:

First: We would see a fireball that would appear to be almost 7 times as big as the sun. The projectile would break up while in flight.and hit the surface with an impact energy of 1.62 x 10^4 MegaTons. A water crater would temporarily form of almost 7 miles in diameter. In the seafloor, a crater of roughly 2 miles in diameter would form.

Then: The major seismic shaking would arrive approximately 37 seconds after impact. Its magnitude on the Richter Scale: 6.3. Dishes, windows, doors would be disturbed; walls would make cracking sounds. Sensation: it would feel like a heavy truck striking the building. Standing cars would rock noticeably.

In 3 1/2 minutes, fine dust and a few bits would shower down in Brooklyn.

The air blast would arrive approximately 9.35 minutes after impact. Max wind velocity: 70.4 mph. Sound intensity: 83 dB (Loud as heavy traffic) Glass windows would shatter.

The impact-generated tsunami wave would arrive approximately 34.7 minutes after impact. Tsunami wave amplitude could be anywhere between 2 and 152 feet. This is a big difference -- but can't be predicted with accuracy because the program doesn't know the actual conditions (the slope of the shore line, the presence of sand bars, etc.).

If we make the asteroid denser (made out of iron) the effects are worse. The airblast will damage roofs, windows will shatter. The tsunami will be deeper.

Have Fun
Have fun playing Impact: Earth! yourself. You can make asteroids of all sizes and densities, traveling different speeds and hitting at different angles. (If we have the Apopsis Asteroid hit at 0 degrees, for example, there's no tsunami at all.)

Top illustration courtesy of Impact: Earth!

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