Near-infrared spectra of icy outer Solar System surfaces: Remote determination of H2O ice temperatures

Wm. Grundy et al., Near-infrared spectra of icy outer Solar System surfaces: Remote determination of H2O ice temperatures, ICARUS, 142(2), 1999, pp. 536-549
Citations number
Categorie Soggetti
Space Sciences
Journal title
ISSN journal
0019-1035 → ACNP
Year of publication
536 - 549
SICI code
We present new 1.20 to 2.35 mu m spectra of satellites of Jupiter, Saturn, and Uranus, and the rings of Saturn, obtained in 1995 and 1998 at Lowell Ob servatory. For most of the target objects, our data provide considerable im provement in spectral resolution and signal-to-noise over previously publis hed data. Absorption bands with shapes characteristic of low-temperature, h exagonal crystalline H2O ice dominate the spectra of most of our targets in this wavelength range. We make use of newly published temperature-dependen t wavelengths and relative strengths of H2O absorption bands to infer ice t emperatures from our spectra. These ice temperatures are distinct from temp eratures determined from thermal emission measurements or simulations of ra diative balances. Unlike those methods, which average over all terrains inc luding ice-free regions, our temperature-sensing method is only sensitive t o the ice component. Our method offers a new constraint which, combined wit h other observations, can lead to better understanding of thermal propertie s and textures of remote, icy surfaces. Ice temperatures are generally lowe r than thermal emission brightness temperatures, indicative of the effects of thermal inertia and segregation between ice and warmer, darker materials . We also present the results of experiments to investigate possible change s of water ice temperature over time, including observations of Titania at two epochs, and of Ganymede and saturnian ring particles following emergenc e from the eclipse shadows of their primary planets. Finally, we discuss li mitations of our temperature measurement method which can result from the p resence of H2O in phases other than hexagonal ice-I-h, such as amorphous ic e, hydrated mineral phases, or radiation-damaged crystalline ice. Our spect ra of Europa and Enceladus exhibit peculiar spectral features which may res ult from effects such as these. (C) 1999 Academic Press.