D
dmjspace
Guest
silylene said: <font color="yellow"> I never said comets and asteroids are the same (I don't think that they are, in fact). </font><br /><br />Good to see the addition of a couple more scientific thinkers around here, rather than usual pseudoskeptical noisemakers.<br /><br />Several people are arguing that comets are not fundamentally the same as asteroids. If that's the case, how are they different?<br /><br />Before the history revision begins (actually, it's too late, but before it gets into high gear), let's go back to what the mainstream model expected from Deep Impact: water, and lots of it.<br /><br />The few estimated densities of comets and asteroids that exist are simply that, estimates. Or, more appropriately, guess-timates.<br /><br />Out of the 2000+ known asteroids, only a dozen or two have any density estimate at all. And we have physical pieces of them on Earth. <br /><br />The comet situation is far worse. <br /><br />Even though we got within 400 miles of comet Halley, there is no definitive data on its density. Whatever your source, there is also no agreement on whether Hally (or any other comet) is a "dirty snowball" or a "snowy dirtball." Luckily, Tempel is probably going to render the errant phrase "dirty snowball" a relic of eras bygone.<br /><br />At which point we'll be stuck with "snowy dirtball," which is precisely what the EPH said comets were all along: asteroids with pockets of volatiles comprising no more than 20% of weight.<br /><br />We frankly don't know anything about comets' true density or composition, a fact which is supported by the very mission we're discussing here, Deep Impact, whose main goal was to see what's inside Tempel.<br /><br />This won't be a newsflash to anyone paying attention: The data show it ain't water in quantities anywhere near expected by the snowball model.<br /><br />Already, even in the posts here, it is quite apparent that snowball model supporters are subconsciously accepting that something drastic needs to be d