NWA 6292

NWA 6292 is paired to NWA 5400, the first find of this unique ungrouped achondrite. It has petrographic and mineralogical similarities to brachinites, but the O-isotopic composition plots on the Terrestrial Fractionation Line (Multi-redundant O-isotope testing was performed by different laboratories around the world)

The difference in Fe/Mn ratios in olivine and pyroxene compared to those in lunar and Earth samples, along with the presence of FeNi-metal, eliminates both objects as the possible source parent body.
It has been proposed that this achondrite may possibly represent a primitive terrene meteorite ejected prior to the collision which spalled the Moon and then stored in the asteroid belt until recent impacts ejected material into an Earth-crossing orbit.
However, age studies revealed a minimum closure age of 4.54 b.y. which is older than the proposed collision of 'Theia' with the proto-Earth. So further speculations consider an origin on 'Theia' itself, prior to its collision with Earth 4.52 b.y. ago, reflecting an original O-isotopic composition indistinguishable from that of the Earth and Moon.

Text source: David Weirs Meteorite Studies






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