Constraints on the surface composition of Trojan asteroids from near-infrared (0.8-4.0μm) spectroscopy

Josh P. Emery, R. H. Brown

Research output: Contribution to journalArticlepeer-review

90 Scopus citations


We present new near-infrared spectra of 20 Trojan asteroids. The spectra were recorded at the NASA Infrared Telescope Facility (IRTF) using the recently commissioned medium-resolution spectrograph SpeX and at the Multiple Mirror Telescope (MMT) using the instrument FSPEC. Spectra of all of these objects were measured in K-band (1.95-2.5 μm), 8 of these in L-band (2.8-4.0 μm), and 14 in the range 0.8-2.5 μm. These observations nearly double the number of published 0.8-2.5 μm spectra of Trojan asteroids and provide the first systematic study of the L-band region for these distant asteroids. The data show that the red spectral slope measured in the near-IR extends through the L-band, though it is not as steep here as at shorter wavelengths. A significant diversity is apparent in the near-IR spectral slopes of this sampling of objects. Most of the spectra do not contain any definitive absorption features characteristic of surface composition (e.g., H2O, organics, silicates) as seen on main-belt asteroids and several Centaur and Kuiper Belt objects. A few objects may display spectral activity, and the reliability of these possible features is discussed. While these spectra are generally compatible with silicate surfaces to explain the spectral slope mixed with some fraction of low albedo material, there is no absolute indication of silicates. The spectral slope could also be explained by the presence of hydrocarbons, but the lack of absorption features, especially in L-band where very strong fundamental absorptions from these molecules appear, constrains the character and abundance of these materials at the surface.

Original languageEnglish (US)
Pages (from-to)104-121
Number of pages18
Issue number1
StatePublished - Jul 1 2003
Externally publishedYes


  • Asteroids, composition
  • Infrared observations
  • Organic chemistry
  • Spectroscopy
  • Surfaces, asteroids

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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