  With a total mass similar to the main asteroid belt, the Jovian Trojan
asteroids are a major feature in the solar system. Based upon the thermal
infrared spectra of the largest Trojans obtained with the Spitzer space
telescope, Emery et al. (2006) suggested that the surfaces of these Trojans may
consist of fine-grained silicates suspended in a transparent matrix.
  To explore the transparent matrix hypothesis, we adopted a modified radiative
transfer model to fit the Trojan spectra simultaneously both in the near and
the thermal infrared regions. Our model shows that the Trojan spectra over a
wide wavelength range can be consistently explained by fine grained silicates
(1-5 wt.%) and highly absorbing material (e.g. carbon or iron, 2-10 wt.%)
suspended in a transparent matrix. The matrix is consistent with a deposit of
salt on the surfaces of the large Trojans. However, this consistency is not an
actual detection of salt and other alternatives may still be possible. We
suggest that early in the Solar System history, short-lived radionuclides
heated ice-rich Trojans and caused melting, internal circulation of water and
dissolution of soluble materials. Briny water volcanism were facilitated by
internal volatiles and a possibly global sill of frozen brine was formed
beneath the cold primitive crust. The frozen brine layer was likely to be
evacuated by impact erosions and evaporation of the exposed brines eventually
left a lag deposit of salt. Over the Solar System's history, fine dust from
comets or impacts contaminated and colored these salty surfaces of the Trojans
to produce the spectral properties observed today.
