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J. P. Emery, R. H. Brown (LPL/University of Arizona)
We will present new analysis of our steadily increasing database of near-IR (0.8 - 4.0 \mum) spectra of Trojan asteroids. To date, we have obtained K-band (1.95 - 2.5 \mum) spectra of 16 objects, I, J, H-band (0.8 - 1.75 \mum) spectra of 7 objects, and L-band (2.8 - 4.0 \mum) spectra of 7 objects. We also have observing time scheduled this fall to add even more Trojan spectra to our collection.
Trojan asteroids orbit the sun at 5.2 AU, trapped in Jupiter’s stable lagrange points. Their unique location beyond the outer edge of the main belt yet interior to Kuiper belt objects and Centaurs gives us the opportunity to study an important transition region and to further examine compositional trends of primitive bodies in the solar system. These asteroids are generally very red and very dark, placing them in the P and D taxonomic classes. The low albedo and red spectral slope, especially in the near-IR, have generally been attributed to organics on the surfaces of these objects, but there has been no direct detection to confirm this hypothesis.
Our data show that the red spectral slope extends through the L-band, though not as steep as at shorter wavelengths. However, we see no evidence for absorptions due to organics, even in the 3.4 mm region where a very strong C-H stretch fundamental would appear. We also see no sign of absorption in the region of the broad, deep, 3 \mum water ice band. We do see some variation in spectral slope even in this small sampling of these objects. We will discuss these issues and more results of our analysis.