Bibcode
Lorenzi, V.; Pinilla-Alonso, N.; Licandro, J.; Cruikshank, D. P.; Grundy, W. M.; Binzel, R. P.; Emery, J. P.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 585, id.A131, 12 pp.
Fecha de publicación:
1
2016
Revista
Número de citas
14
Número de citas referidas
14
Descripción
Context. During the past 30 years the surface of Pluto has been
characterized and its variability monitored through continuous
near-infrared spectroscopic observations. But in the visible range only
a few data are available. Aims: The aim of this work is to define
Pluto's relative reflectance in the visible range to characterize the
different components of its surface, and to provide ground based
observations in support of the New Horizons mission. Methods: We
observed Pluto on six nights between May and July 2014 with the
imager/spectrograph ACAM at the William Herschel Telescope (La Palma,
Spain). The six spectra obtained cover a whole rotation of Pluto
(Prot = 6.4 days). For all the spectra, we computed the
spectral slope and the depth of the absorption bands of methane ice
between 0.62 and 0.90 μm. To search for shifts in the center of the
methane bands, which are associated with dilution of CH4 in
N2, we compared the bands with reflectances of pure methane
ice. Results: All the new spectra show the methane ice absorption
bands between 0.62 and 0.90 μm. Computation of the depth of the band
at 0.62 μm in the new spectra of Pluto and in the spectra of Makemake
and Eris from the literature, allowed us to estimate the Lambert
coefficient at this wavelength at temperatures of 30 K and 40 K, which
has never been measured before. All the detected bands are blueshifted
with respect to the position for pure methane ice, with minimum shifts
correlated to the regions where the abundance of methane is higher. This
could be indicative of a dilution of CH4:N2 that
is more saturated in CH4. The longitudinal and secular
variations in the parameters measured in the spectra are in accordance
with results previously reported in the literature and with the
distribution of the dark and bright materials that show the Pluto's
color maps from New Horizons.