MIR Spectra and Analysis of Jovian Trojan Asteroids

Jovian Trojan asteroids make up a large group of primitive bodies that populate Jupiter's L4 and L5 Lagrange points. The Trojans' dynamics and composition carry insight into the formation mechanisms that shaped our solar system. Mid-infrared (MIR; 5-35 mu m) spectra of Trojans exhibit puzzling silicate emission features, like spectra of optically thin comet comae, which may be interpreted as "fluffy" regoliths. By understanding the physical properties of the regolith (e.g., particle size and regolith porosity), more accurate compositional interpretations can be made. Here we show 14 Spitzer Space Telescope MIR spectra of Trojans and their compositional makeup. Through parameterization of spectral features and comparison to laboratory and remote-sensing spectra, the results show that the Trojans have highly porous regoliths of fine-particulate crystalline (forsterite, enstatite, and possibly a small amount of fayalite and diopside) and amorphous silicates. These results are consistent with a primordial Kuiper Belt origin.