The Surfaces of Pluto and Charon

Much of the surface of Pluto consists of high-albedo regions covered to an unknown depth by Beta-N2, contaminated with CH4, CO, and other molecules. A portion of the exposed surface appears to consist of solid H2O. The remainder is covered by lower albedo material of unknown composition. The N2 ice may occur as polar caps of large extent, leaving ices and other solids of lower volatility in the equatorial regions. The low-albedo material found primarily in the equatorial regions may consist in part of solid hydrocarbons and nitriles produced from N2 and CH4 in the atmosphere or in the surface ices. Alternatively, it may arise from deposition from impacting bodies and/or the chemistry of the impact process itself. Charon's surface is probably more compositionally uniform than that of Pluto, and is covered by H2O ice with possible contaminants or exposures of other materials that are as yet unidentified. The molecular ices discovered on Pluto and Charon have been identified from near-infrared spectra obtained with Earth-based telescopes. The quantitative interpretation of those data has been achieved through the computation of synthetic spectra using the Hapke scattering theory and the optical constants of various ices observed in the laboratory. Despite limitations imposed by the availability of laboratory data on ices in various mixtures, certain specific results have been obtained. It appears that CH4 and CO are trace constituents, and that some fraction of the CH4 (and probably the CO) on Pluto is dissolved in the matrix of solid N2. Pure CH4 probably also occurs on Pluto's surface, allowing direct access to the atmosphere. Study of the nitrogen absorption band at 2.148 micrometers shows that the temperature of the N2 in the present epoch is 40 +/-2 K. The global temperature regime of Pluto can be modeled from observations of the thermal flux at far-infrared and millimeter wavelengths. The low-albedo equatorial regions must be significantly warmer than the polar regions covered by N2 (at T = 40 K) to account for the total thermal flux measured. At the present season, the diurnal skin depth of the insolation-driven thermal wave is small, and the observed mm-wave fluxes may arise from a greater depth. Alternatively, the mm-wave flux may arise from the cool, sublimation source region. The surface microstructure in the regions covered by N2 ice is likely governed by the sintering properties of this highly volatile material. The observed nitrogen infrared band strength requires that expanses of the surface be covered with cm-sized crystals of N2. Grains of H2O ice on Charon, in contrast, are probably of order 50 micrometers in size, and do not metamorphose into larger grains at a significant rate. Because of the similarities in size, density, atmosphere and surface composition between Pluto and Neptune's satellite Triton, the surface structures observed by Voyager on Triton serve as a plausible paradigm for what might be expected on Pluto. Such crater forms, tectonic structures, aeolian features, cryovolcanic structures, and sublimation-degraded topography as are eventually observed on Pluto and Charon by spacecraft will give information on their interior compositions and structures, as well as on the temperature and wind regimes over the planet's extreme seasonal cycle

Cryovolcanic flooding in Viking Terra on Pluto

A prominent fossa trough (Uncama Fossa) and adjacent 28-km diameter impact crater (Hardie) in Pluto's Viking Terra, as seen in the high-resolution images from the New Horizons spacecraft, show morphological evidence of in-filling with a material of uniform texture and red-brown color. A linear fissure parallel to the trough may be the source of a fountaining event yielding a cryoclastic deposit having the same composition and color properties as is found in the trough and crater. Spectral maps of this region with the New Horizons LEISA instrument reveal the spectral signature of H₂O ice in these structures and in distributed patches in the adjacent terrain in Viking Terra. A detailed statistical analysis of the spectral maps shows that the colored H₂O ice filling material also carries the 2.2-μm signature of an ammoniated component that may be an ammonia hydrate (NH₃nH₂O) or an ammoniated salt. This paper advances the view that the crater and fossa trough have been flooded by a cryolava debouched from Pluto's interior along fault lines in the trough and in the floor of the impact crater. The now frozen cryolava consisted of liquid H₂O infused with the red-brown pigment presumed to be a tholin, and one or more ammoniated compounds. Although the abundances of the pigment and ammoniated compounds entrained in, or possibly covering, the H₂O ice are unknown, the strong spectral bands of the H₂O ice are clearly visible. In consideration of the factors in Pluto's space environment that are known to destroy ammonia and ammonia-water mixtures, the age of the exposure is of order ≤10⁹ years. Ammoniated salts may be more robust, and laboratory investigations of these compounds are needed

Cryovolcanic flooding in Viking Terra on Pluto

A prominent fossa trough (Uncama Fossa) and adjacent 28-km diameter impact crater (Hardie) in Pluto's Viking Terra, as seen in the high-resolution images from the New Horizons spacecraft, show morphological evidence of in-filling with a material of uniform texture and red-brown color. A linear fissure parallel to the trough may be the source of a fountaining event yielding a cryoclastic deposit having the same composition and color properties as is found in the trough and crater. Spectral maps of this region with the New Horizons LEISA instrument reveal the spectral signature of H₂O ice in these structures and in distributed patches in the adjacent terrain in Viking Terra. A detailed statistical analysis of the spectral maps shows that the colored H₂O ice filling material also carries the 2.2-μm signature of an ammoniated component that may be an ammonia hydrate (NH₃nH₂O) or an ammoniated salt. This paper advances the view that the crater and fossa trough have been flooded by a cryolava debouched from Pluto's interior along fault lines in the trough and in the floor of the impact crater. The now frozen cryolava consisted of liquid H₂O infused with the red-brown pigment presumed to be a tholin, and one or more ammoniated compounds. Although the abundances of the pigment and ammoniated compounds entrained in, or possibly covering, the H₂O ice are unknown, the strong spectral bands of the H₂O ice are clearly visible. In consideration of the factors in Pluto's space environment that are known to destroy ammonia and ammonia-water mixtures, the age of the exposure is of order ≤10⁹ years. Ammoniated salts may be more robust, and laboratory investigations of these compounds are needed

Pluto: Fluidized Transport of Tholins by Heating of the Subsurface

New Horizons images of Pluto show evidence of the transport of the colored non-ice component across the surface, with substantial accumulations in some areas of low elevation. The non-ice component is presumed to be tholin produced in the atmosphere as a precipitating aerosol, in the surface ices by photolysis or radiolysis, or both. We model the surface layer of N2 ice with varying amounts of incorporated tholin particles to explore the heating within the ice that occurs by the solid-state greenhouse effect. We find that in plausible models of the contaminated N2 surface ice the triple point temperature (63.15K) is reached at a depth of approximately less than 1m. At that depth the confining pressure of the ice column is much less than the triple point pressure (12.52 kPa), so N2 should convert to the gas phase, exerting pressure on the overburden. When the gas pressure exceeds the strength of the confining ice, a breakout on the surface will occur, fluidizing fragments of ice and its contaminants that are then free to flow downhill, rafted on entrained gas, similar in some ways to the pyroclastic volcanic phenomenon known as nue ardente. The digital elevation map of Pluto made from stereo images shows some surface regions that may have been stripped of the N2 layer, exposing H2O ice (presumed to be bedrock) below, with a corresponding accumulation of dark material that was that was the previously entrained particulate tholin. Accumulations of tholin are found associated with some of the fossae, and some cover preexisting topography to depths of up to a few hundred meters

In peace and war : a history of the U.S. merchant marine academy at kings point

Founded in 1937, the U.S. Merchant Marine Academy at Kings Point, New York, has trained more than 20,000 professional mariners�and, in the process, has weathered many turbulent times. In Peace and War draws on extensive research�including archival work and interviews with past and present-day administrators, alumni, and current midshipmen�to document the Academy's evolution from its beginnings to the present. This balanced and comprehensive work details the vision and contributions of determined leaders, both at Kings Point and in Washington, who shaped the Academy. It describes the evolution of the U.S. merchant marine, and explains how a tragic fire aboard the passenger ship SS Morro Castle off the coast of New Jersey�in which the shameful behavior of the ship's crew caused the unnecessary deaths of many passengers�led to the passage of the Merchant Marine Act in 1936, which paved the way for the Academy. It details how Kings Point has adjusted its training and priorities to meet the evolving needs of the nation. For example: visual signaling training was added to the curriculum in response to the growing threat from German subs in the months leading up to World War II. In June 1940, Cadet William O'Reilly's frantic signaling from the SS Washington�a vessel carrying more than 1,700 refugees�averted its sinking by a hostile submarine. From its inception, Kings Point has used the high seas as a campus, with its students shipping out for a full year on commercial vessels to receive a thorough grounding in practical seamanship. In wartime, this has meant that Kings Point cadets often have found themselves in harm's way, and some have paid the ultimate price. Between 1942 and 1945, for example, 142 Kings Point cadets were lost in action, and countless others survived attacks all around the world. At other times, the conflict has been closer to home. The book also describes the Academy's invaluable service after 9/11, when Kings Point personnel and vessels worked around the clock to ferry fire-fighters and rescue personnel to and from nearby Ground Zero in Lower Manhattan. Using compelling examples, In Peace and War conveys the educational experience at the Academy today, including the regiment of midshipmen and the required Sea Year, both of which sharply distinguish Kings Point from almost all other educational institutions. It uses the stories of ten graduates in Norfolk, Virginia, to explain what today's merchant marine is, and to illustrate the wide range of careers and leadership roles for which the Academy prepares its students. Finally, the book details the dedication of the many alumni and other supporters who are committed to continuing Kings Point's contributions to the nation and the maritime industry, and to preserving the proud traditions of this venerable institution