The spectrum of Pluto, 0.40–0.93μm

Abstract

Context. During the past 30 years the surface of Pluto has been characterized and its variability monitored through continuous nearinfrared 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 (P rot = 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 CH 4 in N 2 , 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 CH 4 :N 2 that is more saturated in CH 4 . 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.

COMPLEX HYDROCARBON CHEMISTRY IN INTERSTELLAR AND SOLAR SYSTEM ICES REVEALED: A COMBINED INFRARED SPECTROSCOPY AND REFLECTRON TIME-OF-FLIGHT MASS SPECTROMETRY ANALYSIS OF ETHANE (C2H6) AND D6-ETHANE (C2D6) ICES EXPOSED TO IONIZING RADIATION

“…Also, alkanes were suggested to contribute to certain features in Plutoʼs spectra by studying several linear and branched alkanes diluted in nitrogen ice (Bohn et al 1994). Recently, Lorenzi et al (2016) suggested that the discoloration of Pluto along with Makemake and Eris may be due to COMs, and our present study shows that this is very likely just from the simple ethane ice. Dangi et al (2015) has shown that under model atmospheric conditions containing C3 and C4, hydrocarbons interact catalytically with surfaces of micrometeroids to produce a carbonaceous refractory layer, which can account for the hydrocarbon sequestration.…”

Comprehensive wide-band magnitudes and albedos for the planets, with applications to exo-planets and Planet Nine

“…We did not establish reference magnitude for Pluto in this paper and a search of the literature did not locate values for R C and I C . Therefore we synthesized magnitudes from the spectral profile shown in Figure 3 of Lorenzi et al (2016). Since their data are given as a relative reflectance value rather than in absolute energy units, we adjusted our synthetic magnitudes such that the albedo corresponding to our V value agreed with the average albedo cited in their Table 1.…”

The Dwarf Planet Makemake as seen by X-Shooter

“…The spectral slope measured for Makemake is S M = (21.2 ± 0.6) %/1000 Å and for Eris is S E = (13.5 ± 0.2) %/1000 Å. Notice that these values are not to be directly compared with others in the literature (for instance Lorenzi et al 2016) because these values are dependent of the exact definition used for S , which changes from work to work.…”