Optical spectroscopy of interplanetary dust collected in the Earth's stratosphere

Abstract

A new class of extraterrestrial material has recently become available for study: interplanetary dust particles (2–30 µm in size) collected in the atmosphere at 20-km altitude by inertial impactors mounted on NASA U-2 aircraft in the programme of sampling initiated by Brownlee et al.1. The extraterrestrial nature of a compositionally ‘chondritic’ subset of these particles has been verified by measurements of the elemental and isotopic abundances of noble gases2,3. We report here the first optical absorption spectra of these interplanetary dust particles (IDPs). We show that absorption features in the visible at ∼9,800 cm−1 and in the IR at ∼1,000 cm−1 are present in spectra of these particles. An ∼1,000 cm−1 feature is present in optical spectra of meteorites, comet dust and interstellar dust, although its cause in the latter two is a subject of some debate4,5. Future experimental work on these laboratory samples promises to shed light on the alternatives, at least for particles in the Solar System dust cloud.