Constraining the maximum temperature of atmospheric entry heating of dust particles and the effects of flash heating on He and Ne

Determining the maximum temperatures (T max ) experienced by interplanetary dust particles (IDPs) and micrometeorites (MMs) during atmospheric entry is crucial for interpreting their petrology, volatile content, composition of organics, and textures. We present a new approach for determining T max based on He-release curves acquired by use of a programmable diode laser with active temperature stabilization via the readback from a pyrometer. Flash heating experiments that replicate atmospheric entry conditions were performed on >50 aliquots from five different meteorites: Winchcombe (CM2), PCA 02007 (lunar feldspathic breccia), MIL 090001 (CR2), MIL 090292 (C1-ung.), and NWA 12957 (C3.00-ung.). One to five, 40–250 µm sized grains were flash heated to T max between 500–1600°C, with ramps of 3–12 s and an additional 1–4 s at T max . Subsequently, He-release curves were collected from the flash heated samples and the He and Ne remaining after flash heating was analyzed. The He-release curves show a good separation of the He released from unheated samples up to samples heated to 1200°C. They are therefore well suited to determine the T max of MMs and IDPs during atmospheric entry heating up to 1200°C. The He-release curves are not dependent on the material types, flash heating profiles, noble gas components, He concentrations, or particle sizes. For samples flash heated up to a given temperature between 600 – 1200°C, the peak of the He degassing rates during acquisition of the He-release curves reproducibly occur within a very narrow temperature range. The time separation of the He-release curves in our experiments can only be achieved if several mineral phases with significantly different He-diffusion constants are present in the sample. The He-release curves therefore provide an upper limit to the temperature a sample experienced during a previous heating event. Relative losses of He and Ne during flash heating are predominantly dependent on the T max and mineralogy of the sample and to a lesser degree on the duration of the flash heating pulse. Samples containing a large proportion of phyllosilicates (Winchcombe, MIL 090292) tend to release a larger Ne fraction during flash heating than samples with less or no phyllosilicates (MIL 090001, PCA 02007). About 30–40% of the He and Ne were lost during flash heating to 600°C, losses are typically in the order of 80–90% during flash heating to 1000°C, and there is a near total loss of He and Ne at 1400°C and above.