Adam Hupe wrote: > I am betting that NWA 998 has a different ejection date > and crystallization age than the other five Nakhlites. > The isotope data is proving to be very interesting and > was announced at the 65th Meteoritical Society meeting.
... and pre-atmospheric sizes of martian meteorites: a) The authors estimate the minimum masses of the martian meteoroids to have been in the range of 150�220 kg. b) The 36Cl concentration in Los Angeles is consistent with a meteoroid radius of 20�40 cm. c) The 10Be, 26Al, and 36Cl activities in QUE 94201 indicate a pre-atmospheric radius of 25�40 cm. d) For Shergotty, Bhandari et al. (1986) obtained from the 26Al concentration an effective radius of ~12 cm of the meteoroid, about half the value of 23 cm calculated by Eugster et al. e) Density of the shergottites, Nakhla, and Chassigny is about 3.23, 3.37, and 3.72 g/cm3. f) Model calculations of the upper limit of the radius of fragments ejected from Mars yield radii of <2 m. Don�t these data ring a bell? The next step for meteoriticists (and several people on our List) could be to compare the existing/ recovered masses - especially of documented falls, of course, like Shergotty, Chassigny, Zagami, and Naklha (Watch out, the Nakhla Dog is back in town :-) - to these minimum pre-atmospheric sizes and thus masses. (Model) calculations involving the physics of the falls (heating and ablation, velocity, deceleration, entry angle, strewn field geometry, etc., etc.) might then give us a clue as to if there is still more recoverable material out there. In the case of Shergotty and Chassigny, most if any at all, may have weathered away in the meantime, but Zagami and Nakhla ... Well, we all know that up to 90 % of a meteorite�s mass is lost to ablation which would be close to Zagami�s total recovered mass of about 18.1 kg (well within the 150 - 220 kg interval mentioned by Eugster et al. - 10% => 15-22 kg) but remember the authors say they are minimum masses! If only the discrepancy between the upper limit and the lower limit of the radii wasn�t so huge :-( Best martian regards, Bernd Reference EUGSTER O. et al. (2002) Ejection ages from 81Kr-83Kr dating and pre-atmospheric sizes of martian meteorites (MAPS 37-10, 2002, 1345-1360) ______________________________________________ Meteorite-list mailing list [EMAIL PROTECTED] http://www.pairlist.net/mailman/listinfo/meteorite-list
