Hello Everyone, I feel like an idiot.
I know that trapped atmospheric gases have been found in some martian meteorites but for some unexplained reason, I had always thought that the gases had been incorporated in the rock at the time of formation. I always wondered how gases from the martian atmosphere could have been trapped in a rock at the time it formed, particularly an igneous rock in an underground magma chamber.
Well, thanks to William Cassidy, the man who founded ANSMET, I now realize my assumption was wrong. Cassidy makes it clear that gasses became trapped in martian rocks at the time of the impact which launched the rock from the surface. The rather lengthy quote below is from Cassidy's book "Meteorites, Ice and Antarctica" an excellent book (see more after the quote).
From pages 119-121
EETA 79001 was an important find for another reason. It contained proof that SNC meteorites come from Mars. This meteorite had been highly shocked during the impact that ejected it from the martian surface, and one of the shock effects was to produce pods of glass that had been melted from the constituent minerals of the meteorite by the transient heating generated by shock pressures. The melts that were formed were partly injected along cracks in the rock and partly retained as molten beads at the sites where they formed. Cooling occurred immediately behind the shock wave and the beads were chilled to glass before they could crystalize. Apparently the crater forming asteroid had built up a lense off compressed atmosphere in front of it during it's lengthy trajectory toward the surface of the planet. When it struck the surface it injected highly compressed air into the target rock, and some of this was trapped in the shock-melted inclusions. We know the composition of the martian atmosphere from measurements made by Viking Landers I and II. When some of the glass inclusions were picked out of EETA 79001 and remelted, the gave up their dissolved gases. These gasses when analyzed and corrected for slight terrestrial contamination, contained nitrogen and carbon dioxide in the same abundances as the atmosphere of Mars; they also had isotopes of argon, neon, , krypton, and xenon in the same abundances as does the martian atmosphere. This neat bit of detective work by a number of workers, for the first time tied a SNC meteorite directly to the planet Mars and, through this meteorite, to all the other meteorites.
I love Cassidy's book. If you like meteorites in general, martian and lunar meteorites (like me) and are curious about the ANSMET program and you don't have a copy of this book, you are really missing out. The book is a gold mine of information regarding ANSMET. It is very readable, technical in some places, humorous in others and poignant in others. Some books I love holding and reading and this is one of those books. It is hardbound with glossy pages and nicely illustrated. I like the physical proportion of the book and I even like the dust jacket (I usually abhor dust jackets).
Anyway, many thanks to Dr. Cassidy for clearing that up with me and thanks for writing such a wonderful book.
-Walter Branch ______________________________________________ Visit the Archives at http://www.meteoritecentral.com/mailing-list-archives.html Meteorite-list mailing list Meteorite-list@meteoritecentral.com http://six.pairlist.net/mailman/listinfo/meteorite-list
