Color Trends of Trojan Asteroids Suggest Two Compositional Groups

Details Color Trends of Trojan Asteroids Suggest Two Compositional Groups Color Trends of Trojan Asteroids Suggest Two Compositional Groups

Sep 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.3210e&link_type=abstract

American Astronomical Society, DPS meeting #41, #32.10

Astronomy and Astrophysics

Astronomy

1

Scientific paper

We have measured new near-infrared (0.8 - 2.5 micron) spectra of 71 Trojan asteroids using the SpeX instrument at NASA's Infrared Telescope Facility. The new sample of NIR spectra of Trojans includes smaller objects than we previously observed. These smaller bodies are more likely to have suffered a surface-resetting impact recently, and may therefore show exposures of internal composition. None of the objects we observed show any clear absorptions to within the level of noise in the data. Trojans are generally assumed to be ice and organic rich, but we see no evidence for these materials on the surface of any body that we observed. However, the goal of the observations was a broad survey of a large number of objects, so some of the spectra have relatively low S/N, especially in K-band, that could hide low levels of ices and/or organics.
As expected, spectral slopes of this sample of Trojans range from moderately to very red. Contrary to expectation, however, the distribution of spectral slopes is not continuous. The slopes fall into two groups with a distinct break between them. The difference in slope is concentrated at the shorter end of the spectrum (<1.5 microns); the distribution of H- and K-band slopes is unimodal. Although there is not a lot of overlap in the sample sets, there does appear to be a one-to-one correspondence between the visible color groups previously reported and the NIR spectral groups. The bimodality is present in both the L4 and L5 swarms. We will present the new near-infrared measurements, place them in context with other data on the Trojan asteroids, and discuss the implications for surface compositions and dynamical evolution of the Solar System.
This work has been supported by NASA's Planetary Astronomy program.

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