Bibcode
Cruikshank, D. P.; Pinilla-Alonso, Noemi; Lorenzi, Vania; Grundy, Will M.; Licandro, J.; Binzel, Richard P.
Bibliographical reference
American Astronomical Society, DPS meeting #46, #419.04
Advertised on:
11
2014
Citations
1
Refereed citations
1
Description
We have obtained spectra of the Pluto-Charon pair (unresolved) in the
wavelength range 380-930 nm with resolution ~450 at six roughly equally
spaced longitudes. The data were taken in May and June, 2014, with the
4.2-m Isaac Newton Telescope at Roque de Los Muchachos Observatory in
the Canary Islands, using the ACAM (auxiliary-port camera) in
spectrometer mode, and using two solar analog stars. The new spectra
clearly show absorption bands of solid CH4 at 620, 728, and 850-910 nm,
which were known from earlier work. The 620-nm CH4 band is intrinsically
very weak, and its appearance indicates a long optical pathlength
through the ice. This is especially true if it arises from CH4 dissolved
in N2 ice. Earlier work (Owen et al. Science 261, 745, 1993) on the
near-infrared spectrum of Pluto (1-2.5 µm) has shown that the CH4
bands are shifted to shorter wavelengths because the CH4 occurs as a
solute in beta-phase crystalline N2. The optical pathlength through the
N2 crystals must be on the order of several cm to produce the N2 band
observed at 2.15 µm. The new spectra exhibit a pronounced red
slope across the entire wavelength range; the slope is variable with
longitude, and differs in a small but significant way from that measured
at comparable longitudes by Grundy & Fink (Icarus 124, 329, 1996) in
their 15-year study of Pluto’s spectrum (500-1000 nm). The new
spectra will provide an independent means for calibrating the color
filter bands on the Multispectral Visible Imaging Camera (MVIC) (Reuter
et al. Space Sci. Rev. 140, 129, 2008) on the New Horizons spacecraft,
which will encounter the Pluto-Charon system in mid-2015. They will also
form the basis of modeling the spectrum of Pluto at different longitudes
to help establish the nature of the non-ice component(s) of
Pluto’s surface. It is presumed that the non-ice component is the
source of the yellow-red coloration of Pluto, which is known to be
variable across the surface.