karn@petrus.UUCP (Phil R. Karn) (10/16/85)
The current theme of the Bloom County comic strip (the discovery by Oliver Wendell Jones that Halley's comet will in fact hit the earth on April 11, 1986) got me thinking. The November issue of Scientific American gives the mass of Halley's Comet as 2e14 kg. Now assuming that the impact velocity would be about 70 km/sec (30 km/sec for the earth's orbital motion + guesstimated 40 km/sec for the comet, since it is in a retrograde orbit), the released energy on impact would be about 5e23 J. A kilogram of TNT releases about 4.6e6J; a megaton (English ton) about 4.17e15 J. The collision would therefore be equivalent to about 100 million megatons, in round numbers. This number dwarfs by far even our combined nuclear weapons arsenals. Here's another way to look at it. The energy released by the detonation of 1 kg of TNT is enough to accelerate a 1 kg mass to a velocity of 3,033 m/sec (this is the same as the ideal exhaust velocity were it possible to use TNT in a rocket engine, and real rocket propellants have similar or even higher values). Therefore, a mass traveling at 3 km/s has kinetic energy equivalent to an equal mass of TNT. Kinetic energy goes up as the square of velocity, so Halley's comet at a closing velocity of 70 km/s has 544 times the energy of an equal mass of TNT, and the thing weighs 200 metric gigatons! If anyone has more accurate figures (especially the relative orbital velocities) please let me know. It seems rather unlikely that such a collision would cause the Earth to plummet into the center of the sun, as OWJ predicts, but it would still do a pretty effective job on its life forms. Would anything larger than a microbe survive? Kind of humbling, isn't it? Phil
andrew@alberta.UUCP (Andrew Folkins) (10/16/85)
A few months back, I became temporarily obsessed with 100 metre diameter nickel-iron asteroids. Calculations similar to those in <646@petrus> revealed that these (as asteroids go quite) small pieces of rock would produce megaton-order explosions if one was to hit the Earth. Fortunately, most of this type of material was swept up several billion years ago, and the current odds of an impact of this magnitude are something in the neighbourhood of one every million years. For those of you, like Opus, who are deeply worried about being killed by Halley's Comet, the closest approach is (approximate, I haven't got my Sky & Telescope here) about 30 million miles. Incidentally, did you know that a 100 metre nickel-iron asteroid would be worth several billion dollars as ore? Assuming a density of 8 gm/cm3, the mass of the asteroid would be approximately 24 million metric tonnes of possibly fairly pure nickel iron. This is the approximate equivalent of 5% of the world's TOTAL output of steel, from just one piddling little asteroid. (This doesn't include the gold, platinum, etc. would could be present as impurities). Just think - if someone wanted to put a few nukes to use and try to move an asteroid into Earth orbit, the expedition could practically pay for itself. The metal would be even more useful if used in orbit - how much would it cost to lift that much material from the surface of the Earth? (Anyone for a discussion of the relative merits of asteroids vs. lunar material for orbital construction?) -- Andrew Folkins ...ihnp4!alberta!andrew "Any statements to the effect that this parrot is still a going concern are hereby considered inoperative!"
chongo@nsc.UUCP (Landon Noll) (10/31/85)
In article <646@petrus.UUCP> karn@petrus.UUCP (Phil R. Karn) writes: >The current theme of the Bloom County comic strip (the discovery by >Oliver Wendell Jones that Halley's comet will in fact hit the earth >on April 11, 1986) got me thinking. The strange thing about the comic strip was that the co-ords of impact given in the Sunday strip showed that it would hit about 300 miles due East of Yokohama Japan. Later strips showed an 'X' within Bloom County. What does this all mean? Is O.W.Jones changing his story? chongo <> /\../\
ayers@convexs.UUCP (11/01/85)
>The strange thing about the comic strip was that the co-ords of impact given >in the Sunday strip showed that it would hit about 300 miles due East of >Yokohama Japan. Later strips showed an 'X' within Bloom County. >What does this all mean? Is O.W.Jones changing his story? What this means is that "Bloom County" is larger than you thought...