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  • Chicago Destroyed By Comet

    Posted by Jay Manifold on March 6th, 2004 (All posts by )

    In 1871, that is.


    3 Responses to “Chicago Destroyed By Comet”

    1. Jonathan Says:

      Holy cow!

    2. Jonathan Says:

      OK, seriously: What about the comet core that supposedly fell into Lake Michigan — wouldn’t it have caused huge waves?

    3. Jay Manifold Says:

      I thought you’d never ask. ;)

      A median case, which I assume is for the Pacific Ocean, is described in this abstract. Characterizing the Pacific as a circle of area 155.6 million square km (source), a “median” impact, placed such that half of that area is on either side of a circle with the radius of its location, would occur just under 5,000 km from shore. The stated size of the median impactor is 300 m in diameter and the stated wave height at the shore is 11 meters, with wave penetration of 500-1000 m inshore.

      The half-diameter of Lake Michigan at the Wisconsin-Illinois line is about 60 km. Wave height should vary inversely as the square of the distance to impact and directly as the cube of impactor diameter. A few moments with a calculator establishes that a wave only 1 meter in height at the shoreline could have been produced by a 7-meter-diameter object landing in the middle of the lake. Assuming a relative velocity of 40 km/sec and bulk density of 1 tonne per cubic meter, kinetic energy of impact would have been 34 kT, or about three Hiroshimas. Perhaps someone should check on whether any boats went missing in southern Lake Michigan that night.

      (A related posting on Arcturus, from last September, is here. I discussed a recent near-miss, coincidentally over Chicago, here.)