  The Trojan asteroids remain quite poorly understood, yet their physical
properties provide unique perspective on chemical and dynamical processes that
shaped the Solar System. The current study was undertaken to investigate
surface compositions of these objects. We present 66 new near-infrared (NIR;
0.7 to 2.5 microns) spectra of 58 Trojans, including members of both the
leading and trailing swarms. We also include in the analysis previously
published NIR spectra of 13 Trojans (3 of which overlap with the new sample).
This data set permits not only a direct search for compositional signatures,
but also a search for patterns that may reveal clues to the origin of the
Trojans. We do not report any confirmed absorption features in the new spectra.
Analysis of the spectral slopes, however, reveals an interesting bimodality
among the NIR data. The two spectral groups identified appear to be equally
abundant in the leading and trailing swarms. The spectral groups are not a
result of family membership; they occur in the background, non-family
population. The average albedos of the two groups are the same within
uncertainties (0.051\pm0.016 and 0.055\pm0.016). No correlations between
spectral slope and any other physical or orbital parameter are detected, with
the exception of a possible weak correlation with inclination among the
less-red spectral group. Synthesizing these results with previously published
properties, we conclude that the two spectral groups represent objects with
different intrinsic compositions. We further suggest that while the less-red
group originated near Jupiter or in the main asteroid belt, the redder spectral
group originated farther out in the Solar System. If correct, the Trojan swarms
offer the most readily accessible large reservoir of Kuiper Belt material as
well as a unique reservoir for the study of material from the middle part of
the solar nebula.
