Warren>Here is the situation: A. meteor falls in at somewhat more than escape velocity, perhaps as much as 1.5X escape. This was Barringer's delusion. Stuff is falling in toward the *Sun*, 42.1km/s =rt2*Earth orbital speed, vs 11.2km/s Earth escape speed. So his impactor was (42.1/11.2)^2 ~ 14 times less massive than he thought, and was largely vaporized on impact. Then he had the great misfortune to discover that angled impacts make round craters, and drilled fruitlessly on. --rwg
Something coming in headon would enter at 25+18 = 43 mi/sec. Warren, in your guestimate of the sphere thickness required to escape Venus: the thickness should vary linearly with the surface atmospheric pressure. IIRC, Venus's is ~90 atmospheres. The Earth's surface pressure is about 30 inches of mercury, so a skybound 4" thick steel plate will be facing quite a headwind. I think the most interesting thing about this is that a good fraction of stuff that escapes into interplanetary space will eventually be ejected into interstellar space. So we're broadcasting a wake of bacterial DNA, and should expect some amount of incoming material. I may be out of date, but my impression is that no confirmed extra-solar meteorite has been found. Rich ------ Quoting Bill Gosper <billgosper@gmail.com>:
Warren>Here is the situation: A. meteor falls in at somewhat more than escape velocity, perhaps as much as 1.5X escape.
This was Barringer's delusion. Stuff is falling in toward the *Sun*, 42.1km/s =rt2*Earth orbital speed, vs 11.2km/s Earth escape speed.
So his impactor was (42.1/11.2)^2 ~ 14 times less massive than he thought, and was largely vaporized on impact. Then he had the great misfortune to discover that angled impacts make round craters, and drilled fruitlessly on.
--rwg _______________________________________________ math-fun mailing list math-fun@mailman.xmission.com http://mailman.xmission.com/cgi-bin/mailman/listinfo/math-fun
The Earth's atmospheric density falls off roughly exponentially, with the 1/2 point around 19,000'. So if a body going upwards makes it to this altitude, it has a much better chance of making it out. It isn't very likely, but if a meteor hit the top of a high mountain, the atmosphere wouldn't be nearly the same problem for ejected material. I don't know the details of an impact explosion, but I would expect that the radiation pulse travelling at some fraction of the vacuum speed of light would heat up the atmosphere well ahead of any solid body being ejected, so that the density encountered would be far less than normal. This is analogous to the "Russian torpedo" effect I referred to previously. For example, on hot, humid summer days, it is much harder for airplanes to fly, because the air is significantly less dense. What if the temperature were several thousand degrees instead of 100F ? At 06:22 PM 4/10/2012, rcs@xmission.com wrote:
Something coming in headon would enter at 25+18 = 43 mi/sec.
Warren, in your guestimate of the sphere thickness required to escape Venus: the thickness should vary linearly with the surface atmospheric pressure. IIRC, Venus's is ~90 atmospheres.
The Earth's surface pressure is about 30 inches of mercury, so a skybound 4" thick steel plate will be facing quite a headwind.
I think the most interesting thing about this is that a good fraction of stuff that escapes into interplanetary space will eventually be ejected into interstellar space. So we're broadcasting a wake of bacterial DNA, and should expect some amount of incoming material. I may be out of date, but my impression is that no confirmed extra-solar meteorite has been found.
Rich
------ Quoting Bill Gosper <billgosper@gmail.com>:
Warren>Here is the situation: A. meteor falls in at somewhat more than escape velocity, perhaps as much as 1.5X escape.
This was Barringer's delusion. Stuff is falling in toward the *Sun*, 42.1km/s =rt2*Earth orbital speed, vs 11.2km/s Earth escape speed.
So his impactor was (42.1/11.2)^2 ~ 14 times less massive than he thought, and was largely vaporized on impact. Then he had the great misfortune to discover that angled impacts make round craters, and drilled fruitlessly on.
--rwg
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