Mid-infrared transmission spectra of individual Antarctic micrometeorites and carbonaceous chondrites

Mid-infrared absorption spectra were obtained for 6 carbonaceous chondrites and 6 Antarctic micrometeorites (AMMs) with transmission light using an IR microscope. Obvious absorption bands caused by O-H stretching vibration at 3400cm^ and H-O-H bending vibration at 1640cm^ were detected for CI, CM2,CR2,and CO3 chondrites. All the chondrite samples had Si-O stretching band at around 1000cm^. Allende (CV3) exhibited only Si-O stretching band at near 900cm^ and no O-H bands. Infrared absorption spectra for AMMs showed no O-H stretching vibration reflecting their dry condition, except for F97AC019 and F97AC017 with weak O-H stretching band. Heating experiments on the grains of Murchison and Orgueil with sizes as small as AMMs (∿100μm) were carried out in order to clarify the dehydration effect of micrometeorite during the atmospheric entry. Heating times were 30 and 60s at temperatures every 100℃ from 500℃ to 1000℃. At relatively lower temperature condition (≤700℃), water in carbonaceous chondrites was not depleted. O-H stretching vibration at 3400cm^ was, however, vanished at higher temperature (≥800℃). This might show that AMMs were heated to 800℃ or more during atmospheric entry if our hearting duration is reasonable. Noble gas measurement using laser heating was performed for individual AMMs after the infrared microscopic analyses. Solar-He was detected for 4 samples. F97AC019 with very high concentration of helium (8.1×10^cm^3 STP/g) preserve solar-Ne and primordial trapped argon component. We have discovered an extraordinary AMM, F97AC021,with highly concentrated organic matters. Intense C-H stretching vibration at 2900cm^ and complex absorption pattern appeared in the range from 1400cm^ to 1800cm^ were detected. The AMM might have a potential to have plenty of extraterrestrial organic compounds