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wwh suggested off board I give "astroblemes" the treatment....

I am fortunate to be friends with Drs Jenny and Alex Bevan - wife and husband - and curators of the UWA E de C Clarke Geology Museum and The Minerals and Meteorites department of the Western Australian Museum respectively. A quick call to Jenny helped answer to a very good question from wwh - namely, "How can one calculate the size of the celestial body that created an astrobleme from the size of the crater?

It seems that the answer isn't simple, the crater's size depends upon a number of variables (see green text below). Frinstance, Jenny said that the Hoba meteorite, a 60 ton lump that landed in Africa, left no crater.

Jenny's emailed reply was as follows:

This is a useful page:
http://seds.lpl.arizona.edu/nineplanets/nineplanets/meteorites.html

The diameter of a crater should vary with the cube root of the mass of the impacting meteorite times its velocity squared, but it will depend on the nature of the body and impact site and angle of trajectory.

Impact craters less than 1cm across are found on other bodies in the solar system and are called microcraters (not on Earth, meteorites this size burn up in atmosphere).

Impact craters larger than 300km are called impact basins (again, not on Earth because they date back to early times and Earth processes have obliterated them)

Earth processes work on craters of all sizes to obliterate them. eg. a crater 20km across will be recognisable about 600 million years, whereas craters 1km across will only be recognisable for say 1 million.

An ASTROBLEME (= "star wound") is the eroded remant of an ancient impact crater eg Goss's Bluff. We tend not to use the term once we are sure about it having been a crater, and just say that it is an eroded and/or buried
crater etc., which is probably why you couldn't find a definition easily.

I've checked through the site mentioned above and found it chock-full of good info. I also found a site dedicated to the Barringer Crater in the US but didn't note the URL. It's interesting because, in the early 1900's, Mr Barringer basically did his shirt drilling the base of the crater to find and exploit the fabulous wealth of nickel, iron and diamonds he presumed lay buried. He did not take the news provided by a ballistics expert very well. This chap's experiments showed that any sizeable body travelling at cosmic velocity is completely unaffected by our atmosphere - but totally destroyed the nanosecond it impacts the Earth's surface. So Mr Barringer was looking for something that wasn't there.

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