Many such objects initially have a wide uncertainty in orbit and this rapidly reduces as more orbital data is derived, so something which is assessed as "may hit the earth" initially soon becomes an obvious miss. There is always opportunity for unexpected effects such as outgassing or breakup - the former more for comets. True breakup is usually a gravity induced (?Rorsch limit?) effect and few objects achieve this without already being impact candidates. eg Comet Shoemaker-Levy into Jupiter (if I'm not mixing my comets). Most suitably large objects are well tracked and well known, but there is a constant trickle of now material being discovered. One of these days Ragnarok will arrive. But, it may be next century or in 100+ million years or so. Russell > For a good debunking of the alarmist claims made for TU24 > see the following > post by Astronomer Phil Plait. > > http://www.badastronomy.com/bablog/2008/01/21/repeat-after-me-asteroid-2007- > tu24-is-no-danger-to-earth/ > > Paul Hutch > >> -----Original Message----- >> From: piclist-bounces@mit.edu On Behalf Of Sean Breheny >> Sent: Wednesday, January 23, 2008 1:53 PM >> >> Hi Bob, >> >> I found an article on Space Daily from today saying that >> it will be >> close but not a hit. The min distance they give is >> actually very close >> to what one of the participants in that online forum >> computed by >> running the NASA simulator. I also tried it and got the >> same answer >> (0.004 AU or 371 thousand miles): >> >> http://tinyurl.com/25866o >> >> Sean >> >> >> On Jan 23, 2008 12:31 PM, Bob Axtell >> wrote: >> > http://www.abovetopsecret.com/forum/thread328087/pg1 >> > >> > Russell: heads up. >> > >> > I won't make a comment, but the fact that the topic >> > keeps getting >> > squashed is of some concern... >> > >> > --Bob > > -- -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist