The visible spectrum of Pluto: secular and longitudinal variation

Lorenzi, V.; Pinilla-Alonso, Noemí; Emery, Joshua P.; Licandro, J.; Cruikshank, Dale P.; Grundy, Will; Binzel, Richard P.
Referencia bibliográfica

American Astronomical Society, DPS meeting #47, #210.08

Fecha de publicación:
11
2015
Número de autores
7
Número de autores del IAC
1
Número de citas
0
Número de citas referidas
0
Descripción
Continuous near-infrared spectroscopic observations during the last 30 years enabled the characterization of the Pluto's surface and the study of its variability. Nevertheless, only few data are available in the visible range, where the nature of the complex-organics can be studied.For this reason, we started an observational campaign to obtain the Pluto's relative reflectance in the visible range, with the aim of characterizing the different components of its surface, and providing ground based observations in support of the New Horizons mission. We observed Pluto on six nights in 2014, with the imager/spectrograph ACAM@WHT (La Palma, Spain). We obtained six spectra in the 0.40 – 0.93 µm range, that covered a whole Pluto's rotational period (6.4 days).To study longitudinal variations, we computed for all the spectra the spectral slope, and the position and the depth of the methane ice absorption bands. Also, to search for secular or seasonal variations we compared our data with previously published results.All the spectra present a red slope, indicating the presence of complex organics on Pluto's surface, and show the methane ice absorption bands between 0.73 and 0.90 μm. We also report the detection of the CH4 absorption band at 0.62 μm, already detected in the spectra of Makemake and Eris. The measurement of the band depth at 0.62 μm in the new spectra of Pluto, and in the spectra of Makemake and Eris, permits us to estimate the Lambert coefficient, not measured yet at this wavelength, at a temperature of 30 K and 40 K.We find that all the CH4 bands present a blue shift. This shift is minimum at the Charon-facing hemisphere, where the CH4 is also more abundant, indicating a higher degree of saturation of CH4 in the CH4:N2 dilution at this hemisphere.Comparing with data in the literature, we found that the longitudinal and secular variations of the parameters measured in our spectra are in accordance with previous results and with the distribution of the dark and bright material as showed by the Pluto's albedo maps from New Horizons.In 2015, new observations were run quasi-simultaneously with the New Horizons flyby at 10 different Pluto longitudes (July 3 to 14) . The data are currently being reduced.