New constraints on the surface of Pluto

Abstract

Aims. Spectroscopic investigation of the surface of Pluto allows us to constrain the chemical properties of the volatile species of the solar system reservoir. This permits us to obtain the relative abundances of various molecules, their physical properties, as well as their spatial and temporal variation. This also could tell us about the origin of various minor chemical compounds formed during the solar system formation or generated later on by space weathering. This will give us critical information about the evolution processes that may occur in the entire trans-Neptunian objects population, and in particular the biggest objects, which could retain tenuous atmospheres. Methods. New observations of the surface of Pluto have been carried out along with reanalyses of older observations carried out with the ESO-VLT telescopes and the SINFONI instrument at a mean spectral resolution of 1500. We present three new near-infrared spectra of Pluto observed at different epochs, and covering the H and K spectral bands showing absorption features of methane, nitrogen, and carbon monoxide ices. We ran different spectral models, based on Hapke theory, to constrain the physical and chemical properties of different sides of Pluto. Results. We have confirmed the spatial and secular variation of the spectral properties of the surface of Pluto. The abundances, sizes, and temperatures of different ices, such as CH 4 , CO, and N 2 have been constrained for different parts of the surface of Pluto. The results suggest a temperature probably just above the alpha-beta transition phase of N 2 (close to 36.5 K), and a probable stratification of the dilution state of CO and CH 4 . The presence of minor chemical compounds, such as C 2 H 6 , has been confirmed too, and for data obtained at several sub-Earth east longitudes. Solid C 2 H 4 is suggested by the spectral modeling with abundance variation following that of solid C 2 H 6 and solid CH 4 .

Thermal convection as a possible mechanism for the origin of polygonal structures on Pluto's surface

“…The surface temperature has been constrained using the temperature dependence of the nitrogen absorption spectra. Tryka et al [1994] obtained a temperature of 40 ± 2 K, a result confirmed by more recent studies [e.g., Grundy et al, 2013;Merlin, 2015;Stern et al, 2015]. Considering that the surface temperature is in vapor pressure equilibrium, New Horizons data suggest a surface temperature of 37 ± 3 K [Gladstone et al, 2016].…”

OPTICAL CONSTANTS AND BAND STRENGTHS OF CH4:C2H6 ICES IN THE NEAR- AND MID-INFRARED

“…Some of these hydrocarbons, in particular C 2 H 6 and C 2 H 4 , have also been detected from Earth observations made by Merlin (2015) with the ESO-VLT telescopes and the SINFONI instrument. All these evidences suggest that studies of mixtures of CH 4 and C 2 H x , as those provided in this article, may be helpful on the comprehension of chemical composition and evolution of Pluto's surface.…”

The nitrogen cycles on Pluto over seasonal and astronomical timescales

“…When both CH 4 and N 2 ices are present on the surface, we assume that CH 4 is diluted in a solid solution N 2 :CH 4 with 0.5% of CH 4 , as retrieved from telescopic observations (Merlin, 2015) and overall from the New horizons LEISA spectroscopic data (see spectra g and j in Table 3 in . This modeled N 2 -rich:CH 4 ice sublimes by conserving the 0.5% of diluted CH 4 .…”