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RE: Pluto
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Pluto 'has slushy ocean' below surface

Pluto may harbour a slushy water ocean beneath its most prominent surface feature, known as the "heart".
This could explain why part of the heart-shaped region - called Sputnik Planitia - is locked in alignment with Pluto's main moon Charon.
A viscous ocean beneath the icy crust could have acted as a heavy, irregular mass that rolled Pluto over, so that Sputnik Planitia was facing the moon.
 
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Pluto's icy, slushy heart

Beneath Pluto's "heart" lies a cold, slushy ocean of water ice, according to data from NASA's New Horizons mission. In a paper published today in the journal Nature, the New Horizons team, including researchers from MIT, reports that the dwarf planet's most prominent surface feature - a heart-shaped region named Tombaugh Regio - may harbour a bulging, viscous, liquid ocean just below its surface.
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Title: The Puzzling Detection of X-rays From Pluto by Chandra
Author: C. M. Lisse, R. L. McNutt, Jr., S. J. Wolk, F. Bagenal, S. A. Stern, G. R. Gladstone, T. E. Cravens, M. E. Hill, P. Kollmann, H. A. Weaver, D. F. Strobel, H. A. Elliott, D. J. McComas, R.P. Binzel, B.T. Snios, A. Bhardwaj, A. Chutjian, L. A. Young, C.B. Olkin, K.A. Ennico

Using Chandra ACIS-S, we have obtained imaging Xray spectrophotometry of the Pluto system in support of the New Horizons flyby on 14 July 2015. 174 ksec of observations were obtained on 4 visits in Feb 2014 to Aug 2015. We measured a net signal of 6.8 counts and a noise level of 1.2 counts in a comoving 11 x 11 pixel box (100 x 100 R_Pluto) in the 0.31 to 0.60 keV passband for a detection at > 99.95 C.L. The Pluto photons do not match the background spectrum, are coincident with a 90% flux aperture comoving with Pluto, and are not sky source confused. The mean 0.31 to 0.60 keV Xray power from Pluto is 200 MW, in the midrange of Xray power levels seen for known solar system emission sources: auroral precipitation, solar Xray scattering, and charge exchange (CXE) between solar wind (SW) ions & atmospheric neutrals. We eliminate auroral effects as a source, as Pluto has no known magnetic field & the New Horizons Alice UV spectrometer detected no airglow from Pluto during the flyby. Nano-scale atmospheric haze particles could lead to enhanced resonant scattering of solar X-rays from Pluto, but the energy signature of the detected photons does not match the solar spectrum and estimates of Plutos scattered Xray emission are > 100 times below the 3.9e-5 cps found in our observations. CXE emission from SW carbon, nitrogen, and oxygen ions can produce the energy signature seen, and the 6e25 neutral gas escape rate from Pluto deduced from New Horizons data can support the 3.0e24 Xray photons/sec emission rate required by our observations. Using the SW proton density and speed measured by the Solar Wind Around Pluto (SWAP) instrument in the vicinity of Pluto at the time of the photon emissions, we find too few SW minor ions flowing into the 11 x 11 pixel box centered on Pluto than are needed to support the observed emission rate unless the SW is significantly focused and enhanced in this region.

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Pluto-Charon System
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Title: The Fate of Debris in the Pluto-Charon System
Author: Rachel A. Smullen, Kaitlin M. Kratter

The Pluto-Charon system has come into sharper focus following the fly by of New Horizons. We use N-body simulations to probe the unique dynamical history of this binary dwarf planet system. We follow the evolution of the debris disc that might have formed during the Charon-forming giant impact. First, we note that in-situ formation of the four circumbinary moons is extremely difficult if Charon undergoes eccentric tidal evolution. We track collisions of disc debris with Charon, estimating that hundreds to hundreds of thousands of visible craters might arise from 0.3-5 km radius bodies. New Horizons data suggesting a dearth of these small craters may place constraints on the disc properties. While tidal heating will erase some of the cratering history, both tidal and radiogenic heating may also make it possible to differentiate disc debris craters from Kuiper belt object craters. We also track the debris ejected from the Pluto-Charon system into the Solar System; while most of this debris is ultimately lost from the Solar System, a few tens of 10-30 km radius bodies could survive as a Pluto-Charon collisional family. Most are plutinos in the 3:2 resonance with Neptune, while a small number populate nearby resonances. We show that migration of the giant planets early in the Solar System's history would not destroy this collisional family. Finally, we suggest that identification of such a family would likely need to be based on composition as they show minimal clustering in relevant orbital parameters.

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Title: Orbit classification in the planar circular Pluto-Charon system
Author: Euaggelos E. Zotos

We numerically investigate the orbital dynamics of a spacecraft, or a comet, or an asteroid in the Pluto-Charon system in a scattering region around Charon using the planar circular restricted three-body problem. The test particle can move in bounded orbits around Charon or escape through the necks around the Lagrangian points L1 and L2 or even collide with the surface of Charon. We explore four of the five possible Hill's regions configurations depending on the value of the Jacobi constant which is of course related with the total orbital energy. We conduct a thorough numerical analysis on the phase space mixing by classifying initial conditions of orbits and distinguishing between three types of motion: (i) bounded, (ii) escaping and (iii) collisional. In particular, we locate the different basins and we relate them with the corresponding spatial distributions of the escape and collision times. Our results reveal the high complexity of this planetary system. Furthermore, the numerical analysis shows a strong dependence of the properties of the considered basins with the total orbital energy, with a remarkable presence of fractal basin boundaries along all the regimes. Our results are compared with earlier ones regarding the Saturn-Titan planetary system.

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Title: The Impact Crater Size-Frequency Distribution on Pluto Follows a Truncated Pareto Distribution: Results from a First Data Set Based on the Recent New Horizons' Flyby
Author: L. Zaninetti, F. Scholkmann

Recently it could be shown ( that the impact crater size-frequency distribution of Pluto (based on an analysis of first images obtained by the recent New Horizons flyby) follows a power law alpha = 2.4926 in the interval of diameter (D) values ranging from 3.75 km to the largest determined value of 37.77 km. A reanalysis of this data set revealed that the whole crater SFD (i.e., with values in the interval of 1.2-37.7 km) can be described by a truncated Pareto distribution.

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Pluto may have ice volcanoes

Two possible ice volcanoes have been identified on the surface of Pluto.
They are seen in images returned from the New Horizons probe which flew past the dwarf planet in July.
The mountains are several km high and tens of km across, and each has what appears to be a depression in the top.

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New Horizons: Pluto displays rippling terrain

A great swathe of Pluto that features a strange rippling terrain is perhaps the highlight of the latest image release from the New Horizons mission.
The Nasa probe, which flew by the dwarf planet in July, continues to downlink its data, and as it comes in, the scientists get to work on it.

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Art Meets Science in New Pluto Aerial Tour

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Title: The Spectrum of Pluto, 0.40 - 0.93 m I. Secular and longitudinal distribution of ices and complex organics
Author: V. Lorenzi, N. Pinilla-Alonso, J. Licandro, D. P. Cruikshank, W. M. Grundy, R. P. Binzel, J.P. Emery

Context. During the last 30 years the surface of Pluto has been characterised, and its variability has been monitored, through continuous near-infrared spectroscopic observations. But in the visible range only few data are available.
Aims. The aim of this work is to define the Pluto's relative reflectance in the visible range to characterise 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 m. To search for shifts of the center of the methane bands, 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 m. The computation of the depth of the band at 0.62 m 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 a temperature of 30 K and 40 K, never measured before. All the detected bands are blue shifted, with minimum shifts in correspondence with the regions where the abundance of methane is higher. This could be indicative of a dilution of CH4:N2 more saturated in CH4. The longitudinal and secular variations of 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 material that show the Pluto's albedo maps from New Horizons.

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