RE: Paper on Comet/Asteroid Impact Causing the Younger Dryas Cooling.
May 24, 2013 at 1:55 pm
(This post was last modified: May 24, 2013 at 2:02 pm by Anomalocaris.)
(May 24, 2013 at 1:37 pm)Rhythm Wrote: There are hypothesis about undiscovered and discovered craters (the most strained idea is that the exact crater is a subduction of the canary islands....) - but the idea that the atmosphere -simply must have had- a specific density ignores the density of any given airbursting object. It's not so much an issue of one particular object having a particular density as a issue of one -or the other- object having a particular density. If there was an airburst, it would have more to do with the density of the comet/object, and unfortunately- beyond spherules- we'd be at a loss to demonstrate it.
There is no plausible boilide that would have bulk density much less than water. So density of incoming object is pretty well bounded on the low end. On the lowest end would be a loosely consolidated carbon rich ice ball that has lost most of its other volatiles solids with desnity of around 50% that of water. Even with this low desnity and even it if it were 50 percent carbon, to have enough carbon to make 50 million tons of spherules it would still be almost 400-500 meters across. The reason why I say "it" has enough carbon is because we don't have a crater to suggest it hit and could have made a strewn field out of the ground it struck.
Once any object of a plausible composition and density, whatever its level of consolidation, reaches a certain size (usually around 200-300 meters across), it will survive substantially intact until ground impact (ie, at worst it will impact in a few large pieces representing majority of its original mass, and not a cloud of sand) in most plausible entry geometry because its mass and momentum now would dominate over its structural integrity in its reaction to reentry stress for the duration of atmosphere passage.
Hence the problem. If what is observed is indeed an impact strewn field, the impactor is expected to be too large not to leave a crater.
I concede there could be a crater that we haven't found. But that would seem less likely given how fresh and how large such a crater must be.
Other strewn fields without identified craters are all many scores of times older. The youngest I know of is well over half a million years old.
