This article has an erratum: [erratum]
Volume 526, February 2011
|Number of page(s)||4|
|Section||Planets and planetary systems|
|Published online||24 December 2010|
Goethite as an alternative origin of the 3.1 μm band on dark asteroids
Laboratoire de Planétologie de Grenoble (LPG/IPAG), Université J. Fourier,
CNRS/INSU, UMR5109, OSUG, Université Joseph Fourier,
122 rue de la Piscine,
Grenoble Cedex 9,
2 Institut des Sciences de la Terre (IsTerre), Université J. Fourier, CNRS/INSU, 1381 rue de la piscine, 38041 Grenoble Cedex, France
3 Space Research & Planetary Sciences Division, Physikalisches Institut-Universitaet Bern, Sidlerstrasse 5, 3012 Bern, Switzerland
Received: 1 October 2010
Accepted: 12 November 2010
Context. The reflectance spectra of some main-belt asteroids contain a 3-μm band, which is explained by the presence of water or hydroxyl groups in minerals. Recent observations of 24-Themis have been found to display evidence of water ice.
Aims. We synthesize iron oxy-hydroxide materials and in the laboratory measure their near-infrared spectra under dry conditions to compare with asteroid observations.
Methods. The syntheses are performed using either the well-established titration method or a non-conventional hydrothermal method. Bi-directional near-infrared reflectance spectra are obtained using the spectrogonio radiometer available at LPG/IPAG. Spectra are measured in a vacuum to avoid contamination by adsorbed water.
Results. The reflectance spectra that we measure for synthesized goethite are consistent with published transmission spectra. The 3-μm band in goethite has a minimum around 3.10 μm, similar to observations of 24-Themis. Its overall shape matches well Themis’s 3-μm band; goethite-like oxy-hydroxydes are a viable alternative way of explaining 24-Themis near-IR spectra
Key words: meteorites, meteors, meteoroids / minor planets, asteroids: general / minor planets, asteroids: individual: 24-themis / minor planets, asteroids: individual: 1-Ceres
© ESO, 2010
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