Hi all - Naturally, then, the samples from the Moon preserve a record of what hit and when - whether asteroid or comet. Preserved clasts (from rear spalling) can give some idea of impactor size. Further, the samples preserve a record of what type of asteroid, and when. To top it off, that record goes back to the LPBE.
Of course, that's of limited use for the problem at hand, as the impact dynamics of the Earth-Moon system have never been established. We don't know if the Moon acted a shield for Earth, or vice versa. That's why the cratering rates for the moons of the outer gas giants are so important. Another way of examining the problem is by using the historical record, but the difficulty is that this only samples a small period of time (ca. 10,000 years, or 6,000,000 years when human genetic information is considered). E.P. Grondine Man and Impact in the Americas check amazon.com for availability --- "E.P. Grondine" <[EMAIL PROTECTED]> wrote: > Hi Sterling, Rob, List - > > There is no combined model of asteroid and comet > flux > which accounts for the observed craters on all > bodies > in our solar system. The mechanics of the > Earth-Moon > system have never really been worked out. We really > don't know if the Moon gets hit more often than the > Earth ot less. Shoemaker, who did a lot of the > early > Apollo era work, later renounced a lot of it. > > By the way, no matter what you hear on TV, the > impact > of a comet killed the dinosaurs, not the impact of > an > asteroid. > > thoughts at 4 in the morning, > godd hunting, > Ed > > --- "Sterling K. Webb" > <[EMAIL PROTECTED]> > wrote: > > > Hi, Rob, List, > > > > > > The ratio of the areas of Earth:Moon is > roughly > > 16:1, but > > the deflection caused by Earth's stronger > > gravitational reach > > makes the ratio of impacts about 18:1. > > The lunar impact rate is a more accurate > measure > > of the > > meteroid flux in the vicinity of the Earth's orbit > > than the Earth's > > impact rate is, for that reason. > > Even lunar gravity has a "focusing" effect in > > attracting > > meteroids. The actual "space" flux of meteroids is > > calculated > > to be about 85% to 86% of the rate implied by the > > impact rate > > on the Earth. > > It's much harder to figure out an accurate > rate > > of impacts on > > the Earth, though. As a result, we have no firm > > figure to multiply > > by 0.85. > > > > > > Sterling K. Webb > > > -------------------------------------------------------------------------------- > > > > ----- Original Message ----- > > From: "Rob McCafferty" <[EMAIL PROTECTED]> > > To: <meteorite-list@meteoritecentral.com> > > Sent: Friday, September 01, 2006 3:01 AM > > Subject: Re: [meteorite-list] Meteorites on the > moon > > > > > > > ...lunar impacts are rarer than Earth ones due > to > > the > > > weak gravity of the moon and not just it's > smaller > > > cross-section. > > > > > > Rob McC > > > > > > ______________________________________________ > > Meteorite-list mailing list > > Meteorite-list@meteoritecentral.com > > > http://six.pairlist.net/mailman/listinfo/meteorite-list > > > > > __________________________________________________ > Do You Yahoo!? > Tired of spam? Yahoo! Mail has the best spam > protection around > http://mail.yahoo.com > ______________________________________________ > Meteorite-list mailing list > Meteorite-list@meteoritecentral.com > http://six.pairlist.net/mailman/listinfo/meteorite-list > __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com ______________________________________________ Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
