Extraction of helium from individual interplanetary dust particles by step‐heating

<jats:p><jats:bold>Abstract</jats:bold> Fragments from 20 individual particles, collected in the Earth's stratosphere and believed to be interplanetary dust particles (IDPs), were obtained from NASA's Johnson Space Center collection and subjected to step‐heating to see if differences in the release pattern for <jats:sup>4</jats:sup>He could be observed which might provide clues to the origin of the particles. Comparisons were made to the release pattern for 18 individual lunar surface grains heated in the same manner. Twelve of the IDP fragments contained an appreciable amount of <jats:sup>4</jats:sup>He, 50 percent of which was released by the time the particles were heated to approximately 630 °C. For the 18 individual lunar grains the corresponding average temperature was 660 °C. The <jats:sup>3</jats:sup>He/<jats:sup>4</jats:sup>He ratios found for these fragments agreed well with those found for deep Pacific magnetic fines believed to be of extraterrestrial origin, and were comparable to those which have been observed for the solar wind and lunar surface soil grains. Four of the IDP fragments contained appreciably less <jats:sup>4</jats:sup>He, and this was released at a higher temperature. The remaining four fragments had too little <jats:sup>4</jats:sup>He to permit a determination. From Flynn's analyses of the problem of the heating of IDPs in their descent in the atmosphere, the present results suggest that the parent IDPs of the 12 particles which contained an appreciable amount of <jats:sup>4</jats:sup>He suffered very little heating in their descent and are likely of asteroidal origin, although one cannot rule out the possibility that at least some of them had a cometary origin and entered the earth's atmosphere at a grazing angle. Mineralogical and morphological studies on fragments companion to those used in the present investigation are under way. When these are completed, a more definite picture should emerge.</jats:p>