Remnant extraterrestrial noble gases in Antarctic cosmic spherules
Access this Article
Search this Article
Noble gas abundances in Antarctic cosmic spherules collected from the Tottuki Point on the Soya Coast, Antarctica, are considerably lower than those reported in unmelted micrometeorites, indicating severe heating of the cosmic spherules during atmospheric entry. Although ^3He was below detection limits (2 X 10^<-15> cm^3 STP) in most spherules, ^3He was detectable in three spherules and their ^3He/^4He ratios were close to those of unmelted micrometeorites. Ne and Ar abundances and isotopic compositions were determined for more than half of the spherules. Thirteen samples had high ^<21>Ne/^<22>Ne ratios, possibly reflecting the presence of cosmogenic ^<21>Ne, although blank corrections could not be made for most samples due to the low Ne concentrations. Eight particles had ^<40>Ar/^<36>Ar ratios lower than the atmospheric value of 296, and five of them also had SEP (solar energetic particles)-like Ne, confirming their extraterrestrial origin. These spherules apparently preserve extraterrestrial noble gases in their interiors in spite of severe heating. Sample To440080 has ^<40>Ar/^<36>Ar ratio (566.3±14.8) higher than that of terrestrial atmosphere in spite of the presence of SEP-like Ne, indicating different source material from some spherules and micrometeorites. Extraterrestrial Ne and Ar were not identified in 22 of 31 analyzed spherules, although relative noble gas abundances of fifteen spherules were similar to those of unmelted micrometeorites and clearly distinguishable from terrestrial materials such as terrestrial basalt, air, and water, reflecting their extraterrestrial origin. Since noble gas abundances in Antarctic spherules can be explained as mixtures of solar and Q-components and the contribution of adsorption air is insignificant, a majority of these Antarctic spherules represent accreted extraterrestrial material and are not volcanic products.
- Antarctic meteorite research
Antarctic meteorite research (16), 196-219, 2003-03