Neon produced by solar cosmic rays in ordinary chondrites

Roth, Antoine S. G.; Trappitsch, Reto; Metzler, Knut; Hofmann, Beda A.; Leya, Ingo (2017). Neon produced by solar cosmic rays in ordinary chondrites. Meteoritics & planetary science, 52(6), pp. 1155-1172. Meteoritical Society at the University of Arkansas, Dept. of Chemistry and Biochemistry 10.1111/maps.12868

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Solar-cosmic-ray-produced Ne (SCR-Ne), in the form of low cosmogenic ²¹Ne/²²Ne ratios (²¹Ne/²²Necos <0.8), is more likely to be found in rare meteorite classes, like Martian meteorites, than in ordinary chondrites. This may be the result of a sampling bias: SCR-Ne is better preserved in meteorites with small preatmospheric radii and these specimens are often only studied if they belong to unusual or rare classes. We measured He and Ne isotopic concentrations and nuclear tracks in 25 small unpaired ordinary chondrites
from Oman. Most chondrites have been intensively heated during atmospheric entry as
evidenced by the disturbed track records, the low ³He/²¹Ne ratios, the low 4He concentrations, and the high peak release temperatures. Concentration depth profiles
indicate significant degassing; however, the Ne isotopes are mainly undisturbed.
Remarkably, six chondrites have low ²¹Ne/²²Necos in the range 0.711–0.805. Using a new physical model for the calculation of SCR production rates, we show that four of the
chondrites contain up to ~20% of SCR-Ne; they are analyzed in terms of preatmospheric
sizes, cosmic ray exposure ages, mass ablation losses, and orbits. We conclude that SCR-Ne is preserved, regardless of the meteorite class, in specimens with small preatmospheric radii. Sampling bias explains the predominance of SCR-Ne in rare meteorites, although we cannot exclude that SCR-Ne is more common in Martian meteorites than it is in small ordinary chondrites.

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