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 I may be out of date, but my impression is that no confirmed extra-solar meteorite has been found.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