Hi All, I was going to answer Patrick's question about captured natural satellites, but Frank's reply was excellent. It covers the basic problem -- explaining why asteroid capture is virtually impossible as a 2-body problem -- but even better, it discusses an extremely rare case where it could happen (if only briefly): > But what if the asteroid passes very close to the Earth and enters the upper > atmosphere? Friction and atmospheric pressure ... can irreversibly reduce > the energy of the meteor. Usually this ends with the meteor[oid] entering the > lower atmosphere and burning up. But it's also possible for a meteor[oid] to > skip out of the atmosphere. In that case, you would have an object with a > speed quite possibly reduced below Earth's escape velocity. ... > Unfortunately, the perigee of the bound orbit would necessarily be located > at the point in the atmosphere where the moonlet experienced its deceleration. > ... The moonlet would almost certainly enter on the next orbit and be > destroyed in the atmosphere. For those who weren't aware, this exact scenario actually played itself out less than four years ago. A meteoroid first entered Earth's atmosphere around 8 pm MDT on October 3, 1996, east of Las Cruces, NM, heading east-northeast on a very shallow trajectory. Aerodynamic forces began to break it apart as it crossed over the Texas Panhandle, showering the area with a brilliant meteor display. However, the main fragment retained sufficient momentum to continue back out of the atmosphere (greatly decelerated). Its velocity reduced from >40,000 mph to ~18,000 mph, the meteoroid went into Earth orbit. 100 minutes later, the meteoroid entered the atmosphere a second time, this time for good. It crossed the California coastline near Point Conception, passed just north of Bakersfield and reentered somewhere northeast of Kernville -- possibly as far as Owens Valley. Sonic booms were heard throughout the area. Unfortunately, meteorites from this fall have yet to be found. --Rob ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html
This archive was generated by hypermail 2b29 : Fri Jun 09 2000 - 11:25:32 PDT