Newsgroups: sci.astro,alt.sci.planetary,alt.astronomy,sci.astro.amateur,
	sci.geo.geology
From: henry@spsystems.net (Henry Spencer)
Subject: Re: New Mars Meteorite Found In California
Date: Tue, 8 Feb 2000 18:42:33 GMT

In article <200002081603181108301@grenoble-11-115.abo.wanadoo.fr>,
Jean Pelmont <jean.pelmont@wanadoo.fr> wrote:
>1) What are the sound criteria used to ascertain that the stone is
>coming from Mars, and not from somewhere else through space ?

Well, the smoking pistol is that a couple of the Mars meteorites were
partly melted during the event that threw them off Mars, and there are air
bubbles trapped in the melt, and the gas in those bubbles matches the
chemical and isotopic composition of the Martian atmosphere (as measured
by the Viking landers) exactly.

However, the way most Mars meteorites are positively identified is that
their oxygen-isotope ratios match those of the ones with the gas bubbles,
and don't match those of other meteorite types, Earth/Moon rocks, etc.
(Because there are *three* stable oxygen isotopes, you can use the O16/O17
ratio to pretty much calibrate out the effect of mass-sensitive chemical
processes on the O16/O18 ratio.)
--
The space program reminds me        |  Henry Spencer   henry@spsystems.net
of a government agency.  -Jim Baen  |      (aka henry@zoo.toronto.edu)