The 3 $\mu$m Spectrum of Jupiter's Irregular Satellite Himalia

Abstract

We present a medium resolution spectrum of Jupiter's irregular satellite Himalia covering the critical 3 $\mu$m spectral region. The spectrum shows no evidence for aqueously altered phyllosilicates, as had been suggested from the tentative detection of a 0.7 $\mu$m absorption, but instead shows a spectrum strikingly similar to the C/CF type asteroid 52 Europa. 52 Europa is the prototype of a class of asteroids generally situated in the outer asteroid belt between less distant asteroids which show evidence for aqueous alteration and more distant asteroids which show evidence for water ice. The spectral match between Himalia and this group of asteroids is surprising and difficult to reconcile with models of the origin of the irregular satellites.