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Abstract-The trace element compositions and noble gas contents of 32 individual interplanetary dust particles (IDPs) collected in the Earth's stratosphere were measured. Trace element compositions are generally similar to CI meteorites, with occasional depletions in ZnRe with respect to CI. Noble gases were detected in all but one of the IDPs. Noble gas elemental compositions are consistent with the presence of fractionated solar wind. A rough correlation between surface-normalized He abundances and ZnIFe ratios is observed; Zn-poor particles generally have lower He contents than the other IDPs. This suggests that both elements were lost by frictional heating during atmospheric entry and confirms the view that Zn can serve as an entry-heating indicator in IDPs. INTRODUCTIONApproximately 30 000 metric tons of cosmic dust rains down on the Earth each year . Most of this material is melted or vaporized by frictional heating during atmospheric entry. Because entry heating scales with Earth-encounter velocity, size and density, small (less than -50 pm), low-speed (<20 kmh) particles can survive entry without significant melting. Dust grains in t h s size range, known as interplanetary dust particles (IDPs), subsequently settle through the stratosphere at rates of a few centimeters per second (Brownlee, 1985, and references therein). IDPs are now routinely collected using NASA ER-2 high altitude research aircraft (Zolensky et al., 1984). Collected particles are archved at the cosmic dust laboratory at NASA's Johnson Space Center (JSC) where they are made conveniently available for approved research.Most IDPs appear to be more primitive than CI chondrites. On theoretical grounds, it is expected that IDPs probably sample a wider range of ancient parent objects than do meteorites, including comets and distant asteroids (e.g., Kortenkamp et al., 2001). However deciphering the primitive record in these particles is complicated by the fact that all were heated to some degree during atmospheric entry. Alterations from entry heating are often subtle and may include the presence of a magnetite rim (e.g., Keller et al., l992), the inferred annealing of solarflare heavy ion tracks, thermal alteration of a particle's infrared spectrum (Sandford and Bradley, 1989) or solar-He release profile , apparent loss of volatile trace elements , andor partial or complete melting.It is important to be able to identify entry-heating alterations in IDPs so that they can be distinguished from primordial features. In addition, several researchers have pointed out that the connection between the degree of frictional heating and entry velocity may permit delineation of IDPs from high speed source objects such as comets (e.g., Flynn, 1989; Nier, 1994).Heating indicators based on the concentrations of volatile trace elements are particularly attractive because such elements can be measured non-destructively using x-ray fluorescence spectroscopy. Previous trace element analyses have revealed that -25% of all IDPs are depleted in the volatile element...

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