On Mar 11, 8:55 pm, bob haller <hall...@aol.com> wrote: > On Mar 11, 1:34 pm, Robert Clark <rgregorycl...@yahoo.com> wrote: > ... > > Now note that trillions to one odds are such that we would not expect > > it to happen during the entire age of the Solar System. > > > Bob Clark > > perhaps this area of space has more debris, or something unknown is > distorting their orbits?
Here are some suggested physical phenomena that could cause periodic cometary impacts that were proposed to explain the periodic extinctions that have been observed in Earth's fossil record:
Another perhaps more benign explanation is a theory proposed in 2007 there should be an increase in the number of sun grazing comets the next few years:
Kreutz Sungrazers "Several members of the Kreutz family have become Great Comets, occasionally visible near the Sun in the daytime sky. The most recent of these was Comet Ikeya?Seki in 1965, which may have been one of the brightest comets in the last millennium. It has been suggested that another cluster of bright Kreutz system comets may begin to arrive in the inner Solar System in the next few years to decades." http://en.wikipedia.org/wiki/Kreutz_Sungrazers
This appears to have been validated:
"Suicide" Comet Storm Hits Sun?Bigger Sun-Kisser Coming? Andrew Fazekas for National Geographic News Published January 17, 2011 [Quote]A recent storm of small comets that pelted the sun could herald the coming a much bigger icy visitor, astronomers say. Since its launch in 1995, NASA's Solar and Heliospheric Observatory, or SOHO, orbiter has captured pictures of 2,000 comets as they've flown past the sun. Most of these comets are so-called sungrazers, relatively tiny comets whose orbits bring them so near the sun that they are often vaporized within hours of discovery. The sun-watching telescope usually picks up one sungrazer every few days. But between December 13 and 22, SOHO saw more than two dozen sungrazers appear and disintegrate. Seeing "25 comets in just ten days, that's unprecedented," Karl Battams, of the United States Naval Research Laboratory in Washington, D.C., said in a statement. "It was crazy!" According to Battams and colleagues, the comet swarm could be forerunner fragments from a much larger parent comet that may be headed along a similar path. And such a large icy body coming so near the sun would result in a spectacular sky show.[/quote] http://news.nationalgeographic.com/news/2011/01/110117-comets-storm-sun-soho-nasa-sungrazing-science-space/
It's interesting this prediction of the SOHO scientists appears to be confirmed by the discovery of the sungrazing Comet ISON in September, 2012, expected to be one of the brightest comets in history
In any case an increase of sun grazers could also correspond to an increase in close flybys of comets by the terrestrial planets. A problem though is this increase could itself be due to a disruption of the comets in the Oort Cloud.