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 gases^2,3. 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 debate^4,5. Future experimental work on these laboratory samples promises to shed light on the alternatives, at least for particles in the Solar System dust cloud.