Spectral calibration for deriving surface mineralogy of Asteroid (25143) Itokawa from Hayabusa Near-Infrared Spectrometer (NIRS) data

Megha Bhatt, Vishnu Reddy, Lucille Le Corre, Juan A. Sanchez, Tasha Dunn, Matthew R.M. Izawa, Jian Yang Li, Kris J. Becker, Lynn Weller

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1 Citation (Scopus)

Abstract

We present spectral calibration equations for determining mafic silicate composition of near-Earth asteroid (25143) Itokawa from visible/near-infrared (VNIR) spectra (0.85-2.1. μm) measured using the Near Infrared Spectrometer (NIRS) on board the Japanese Hayabusa spacecraft. Itokawa was the target of the Hayabusa sample return mission and has a surface composition similar to LL chondrites. Existing laboratory spectral calibrations (e.g., Dunn, T.L. et al. [2010]. Icarus 208, 789-797) use a spectral wavelength range that is wider (0.75-2.5. μm) than that of the NIRS instrument (0.85-2.1. μm), making them unfit for interpreting the Hayabusa spectral data currently archived in the Planetary Data System (PDS). We used laboratory near-infrared (NIR) reflectance spectra of ordinary chondrites (H, L and LL) from the study of Dunn et al. (Dunn, T.L. et al. [2010]. Icarus 208, 789-797), which we resampled to the NIRS wavelength range. Using spectral parameters extracted from these resampled spectra we established a relationship between band parameters and mafic silicate compositions (olivine and low-Ca pyroxene). We found a correlation >90% between mafic silicate compositions (fayalite and ferrosilite mol.%) estimated by our spectral method, and electron microprobe measured values from Dunn et al. (Dunn, T.L. et al. [2010]. Icarus 208, 789-797). The standard deviation between the measured and estimated values is 1.5 and 1.1. mol.% for fayalite and ferrosilite, respectively. To test the validity of the new equations we blind tested them using nine laboratory spectra of L and LL chondrites with well-known compositions. We found that the absolute difference between the measured and computed values is in the range 0.1-1.6. mol.%. Our study demonstrates that this new calibration is robust and can be applied to Hayabusa NIRS data despite its limited spectral range (0.85-2.1. μm). We applied the equations to a subset of uncalibrated (no photometric corrections) NIRS spectra and we obtained fayalite and ferrosilite values that are consistent with Itokawa having a LL chondrite surface composition. We intend to develop a photometric model to calibrate the NIRS spectra to standard viewing geometry and apply the new equations to create a global mineralogical map of Itokawa.

Original languageEnglish
Pages (from-to)124-130
Number of pages7
JournalIcarus
Volume262
DOIs
Publication statusPublished - Dec 1 2015
Externally publishedYes

Keywords

  • Asteroid Itokawa
  • Asteroids, composition
  • Asteroids, surfaces
  • Meteorites
  • Spectroscopy

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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