The only thing I'd add to Jim's response is that it wasn't that long ago that finding new minor planets was easy. In the mid 90s there was an article in S&T by Dennis DeCicco where he wrote about taking a picture of the sky (with a film camera, BTW) and caught several previously unknown MPs. But now with the professional searches on line it has become much more difficult for amateurs to make discoveries (which is why most of what I do these days it make light curves of already known MPs). And with the new surveys coming on line which will have the ability to search the entire sky down to magnitude 20 every three days I think it's pretty safe to say that if there are still any undetected planet killers out there they wont stay undetected for long. patrick p.s. For those with a serious interest in MPs, here's where to find the MPML Jim referred to: http://tech.groups.yahoo.com/group/mpml On 27 Jan 2009, at 16:49, Jim Gibson wrote:
Rich wrote: It's nothing that those on this board haven't thought about but, the chances of a cataclysmic collision occurring in our lifetime is a reality. It is a scary reality! I wonder, is the monitoring of near earth objects as comprehensive as it needs to be? Do we have automated monitors or are we depending on human observation?
Patrick will probably give the definitive answer on this but, he is still asleep I think. Patrick led me to the Yahoo Minor Planetary and something or other Yahoo group. Those boys seem to feel things are pretty well under control.
Quoting Alain Maury he states: “Apart from the very very very unlikely long period comet arriving from the Oort cloud and falling just on us, there are no more objects able to "end life as we know it" anywhere in the solar system which has not been detected. We are at the 70%, 80% level on the 1km diameter asteroids (or better phrased magnitude 18 and brighter asteroids), and a "global killer" is more like a 10km asteroid, and we all know them and none is anywhere near an impacting orbit.”
He goes on to say:
“Very quickly (let's say another 5 years of hard work), the only worry left will be in the 200m range, i.e. "state" destroyers, not "continent destroyers".
So if these guys know what they are talking about then your statement “, the chances of a cataclysmic collision occurring in our lifetime” still may be true but should not be to the point of “scary” I think.
For what it’s worth
Jim Gibson