The Global Color of Pluto from New Horizons Olkin, Catherine B.; Spencer, John R.; Grundy, William M. ...
The Astronomical journal,
12/2017, Letnik:
154, Številka:
6
Journal Article
Recenzirano
Odprti dostop
The New Horizons flyby provided the first high-resolution color maps of Pluto. We present here, for the first time, an analysis of the color of the entire sunlit surface of Pluto and the first ...quantitative analysis of color and elevation on the encounter hemisphere. These maps show the color variation across the surface from the very red terrain in the equatorial region, to the more neutral colors of the volatile ices in Sputnik Planitia, the blue terrain of East Tombaugh Regio, and the yellow hue on Pluto's North Pole. There are two distinct color mixing lines in the color-color diagrams derived from images of Pluto. Both mixing lines have an apparent starting point in common: the relatively neutral-color volatile-ice covered terrain. One line extends to the dark red terrain exemplified by Cthulhu Regio and the other extends to the yellow hue in the northern latitudes. There is a latitudinal dependence of the predominant color mixing line with the most red terrain located near the equator, less red distributed at mid-latitudes and more neutral terrain at the North Pole. This is consistent with the seasonal cycle controlling the distribution of colors on Pluto. Additionally, the red color is consistent with tholins. The yellow terrain (in the false color images) located at the northern latitudes occurs at higher elevations.
•The Alice instrument on New Horizons measured a UV solar occultation by Pluto's atmosphere in 2015.•Densities were derived for N2, CH4, C2H2, C2H4, C2H6, and haze.•These imply low escape rates ...(CH4-dominated), a stable lower atmosphere, direct evidence for C2Hx photochemistry, and haze whose extinction coefficient is roughly proportional to N2 density.
The Alice instrument on NASA's New Horizons spacecraft observed an ultraviolet solar occultation by Pluto's atmosphere on 2015 July 14. The transmission vs. altitude was sensitive to the presence of N2, CH4, C2H2, C2H4, C2H6, and haze. We derived line-of-sight abundances and local number densities for the 5 molecular species, and line-of-sight optical depth and extinction coefficients for the haze. We found the following major conclusions: (1) We confirmed temperatures in Pluto's upper atmosphere that were colder than expected before the New Horizons flyby, with upper atmospheric temperatures near 65–68 K. The inferred enhanced Jeans escape rates were (3–7) × 1022 N2 s−1 and (4–8) × 1025 CH4 s−1 at the exobase (at a radius of ∼ 2900 km, or an altitude of ∼1710 km). (2) We measured CH4 abundances from 80 to 1200 km above the surface. A joint analysis of the Alice CH4 and Alice and REX N2 measurements implied a very stable lower atmosphere with a small eddy diffusion coefficient, most likely between 550 and 4000 cm2 s−1. Such a small eddy diffusion coefficient placed the homopause within 12 km of the surface, giving Pluto a small planetary boundary layer. The inferred CH4 surface mixing ratio was ∼ 0.28–0.35%. (3) The abundance profiles of the “C2Hx hydrocarbons” (C2H2, C2H4, C2H6) were not simply exponential with altitude. We detected local maxima in line-of-sight abundance near 410 km altitude for C2H4, near 320 km for C2H2, and an inflection point or the suggestion of a local maximum at 260 km for C2H6. We also detected local minima near 200 km altitude for C2H4, near 170 km for C2H2, and an inflection point or minimum near 170–200 km for C2H6. These compared favorably with models for hydrocarbon production near 300–400 km and haze condensation near 200 km, especially for C2H2 and C2H4 (Wong et al., 2017). (4) We found haze that had an extinction coefficient approximately proportional to N2 density.
•The analysis of the first couple of LEISA/New Horizons spectro-images is performed.•Qualitative distribution maps are obtained for N2, CH4, CO, H2O and the red material.•3 different types of ices ...are found: N2-rich:CH4:CO, CH4-rich(:CO:N2?) and H2O ices.•Sublimation sequence transforms N2-rich ice to CH4-rich ice through a binary mixture.
From Earth based observations Pluto is known to be the host of N2, CH4 and CO ices and also a dark red material. Very limited spatial distribution information is available from rotational visible and near-infrared spectral curves obtained from hemispheric measurements. In July 2015 the New Horizons spacecraft reached Pluto and its satellite system and recorded a large set of data. The LEISA spectro-imager of the RALPH instruments are dedicated to the study of the composition and physical state of the materials composing the surface. In this paper we report a study of the distribution and physical state of the ices and non-ice materials on Pluto's illuminated surface and their mode and degree of mixing. Principal Component analysis as well as various specific spectral indicators and correlation plots are used on the first set of 2 high resolution spectro-images from the LEISA instrument covering the whole illuminated face of Pluto at the time of the New Horizons encounter. Qualitative distribution maps have been obtained for the 4 main condensed molecules, N2, CH4, CO, H2O as well as for the visible-dark red material. Based on specific spectral indicators, using either the strength or the position of absorption bands, these 4 molecules are found to indicate the presence of 3 different types of ices: N2-rich:CH4:CO ices, CH4-rich(:CO:N2?) ices and H2O ice. The mixing lines between these ices and with the dark red material are studied using scatter plots between the various spectral indicators. CH4 is mixed at the molecular level with N2, most probably also with CO, thus forming a ternary molecular mixture that follows its phase diagram with low solubility limits. The occurrence of a N2-rich – CH4-rich ices mixing line associated with a progressive decrease of the CO/CH4 ratio tells us that a fractionation sublimation sequence transforms one type of ice to the other forming either a N2-rich – CH4-rich binary mixture at the surface or an upper CH4-rich ice crust that may hide the N2-rich ice below. The strong CH4-rich – H2O mixing line witnesses the subsequent sublimation of the CH4-rich ice lag left behind by the N2:CO sublimation (N spring-summer), or a direct condensation of CH4 ice on the cold H2O ice (S autumn). The weak mixing line between CH4-containing ices and the dark red material and the very sharp spatial transitions between these ices and this non-volatile material are probably due to thermal incompatibility. Finally the occurrence of a H2O ice – red material mixing line advocates for a spatial mixing of the red material covering H2O ice, with possibly a small amount intimately mixed in water ice. From this analysis of the different materials distribution and their relative mixing lines, H2O ice appears to be the substratum on which other ices condense or non-volatile organic material is deposited from the atmosphere. N2-rich ices seem to evolve to CH4-dominated ices, possibly still containing traces of CO and N2, as N2 and CO sublimate away. The spatial distribution of these materials is very complex.
The high spatial definition of all these composition maps, as well as those at even higher resolution that will be soon available, will allow us to compare them with Pluto's geologic features observed by LORRI panchromatic and MVIC multispectral imagers to better understand the geophysical processes in action at the surface of this astonishingly active frozen world.
The flyby of Pluto and Charon by the New Horizons spacecraft provided high-resolution images of cratered surfaces embedded in the Kuiper belt, an extensive region of bodies orbiting beyond Neptune. ...Impact craters on Pluto and Charon were formed by collisions with other Kuiper belt objects (KBOs) with diameters from ~40 kilometers to ~300 meters, smaller than most KBOs observed directly by telescopes. We find a relative paucity of small craters ≲13 kilometers in diameter, which cannot be explained solely by geological resurfacing. This implies a deficit of small KBOs (≲1 to 2 kilometers in diameter). Some surfaces on Pluto and Charon are likely ≳4 billion years old, thus their crater records provide information on the size-frequency distribution of KBOs in the early Solar System.
NASA's New Horizons spacecraft has revealed the complex geology of Pluto and Charon. Pluto's encounter hemisphere shows ongoing surface geological activity centered on a vast basin containing a thick ...layer of volatile ices that appears to be involved in convection and advection, with a crater retention age no greater than ~10 million years. Surrounding terrains show active glacial flow, apparent transport and rotation of large buoyant water-ice crustal blocks, and pitting, the latter likely caused by sublimation erosion and/or collapse. More enigmatic features include tall mounds with central depressions that are conceivably cryovolcanic and ridges with complex bladed textures. Pluto also has ancient cratered terrains up to ~4 billion years old that are extensionally faulted and extensively mantled and perhaps eroded by glacial or other processes. Charon does not appear to be currently active, but experienced major extensional tectonism and resurfacing (probably cryovolcanic) nearly 4 billion years ago. Impact crater populations on Pluto and Charon are not consistent with the steepest impactor size-frequency distributions proposed for the Kuiper belt.
Recent observations of interplanetary medium atomic hydrogen Lyman‐α emission in the outer solar system, made with the Alice ultraviolet spectrograph on New Horizons, are presented. The observations ...include regularly spaced great circle scans of the sky and pointed observations near the downstream and upstream flow directions of interstellar H atoms. The New Horizons Alice data agree very well with the much earlier Voyager UVS results, after these are reduced by a factor of 2.4 in brightness, in accordance with recent reanalyses. In particular, the falloff of interplanetary medium Lyman‐α brightness in the upstream‐looking direction as a function of spacecraft distance from the Sun is well matched by an expected 1/r dependence, but with an added constant brightness of ~40 Rayleighs. This additional brightness is a possible signature of the hydrogen wall at the heliopause or of a more distant background. Ongoing observations are planned at a cadence of roughly twice per year.
Plain Language Summary
Long‐term observations made with the Alice instrument on the New Horizons spacecraft confirm measurements made 30 years earlier with the Voyager spacecraft. Both sets of data are best explained if the observed ultraviolet light is not only a result of the scattering of sunlight by hydrogen atoms within the solar system but includes a substantial contribution from a distant source. This distant source could be the signature of a “wall” of hydrogen, formed near where the interstellar wind encounters the solar wind, or could be more distant. Similar future observations from New Horizons are planned about twice each year.
Key Points
New Horizons Alice observations of interplanetary medium Lyman alpha are presented
The observed brightness falloff with distance from the Sun matches well with Voyager results and indicates a substantial external background contribution
The atmosphere of Pluto as observed by New Horizons Gladstone, G. Randall; Stern, S. Alan; Ennico, Kimberly ...
Science (American Association for the Advancement of Science),
03/2016, Letnik:
351, Številka:
6279
Journal Article
Recenzirano
Odprti dostop
Observations made during the New Horizons flyby provide a detailed snapshot of the current state of Pluto's atmosphere. Whereas the lower atmosphere (at altitudes of less than 200 kilometers) is ...consistent with ground-based stellar occultations, the upper atmosphere is much colder and more compact than indicated by pre-encounter models. Molecular nitrogen (N2) dominates the atmosphere (at altitudes of less than 1800 kilometers or so), whereas methane (CH4), acetylene (C2H2), ethylene (C2H4), and ethane (C2H6) are abundant minor species and likely feed the production of an extensive haze that encompasses Pluto. The cold upper atmosphere shuts off the anticipated enhanced-Jeans, hydrodynamic-like escape of Pluto's atmosphere to space. It is unclear whether the current state of Pluto's atmosphere is representative of its average state--over seasonal or geologic time scales.
One component of the REX instrument on NASA's New Horizons spacecraft was an investigation of the radio continuum radiation from Pluto and Charon during the flyby on 14 July 2015. The planetary ...thermal emission was recorded at a wavelength of 4.17 cm (7.18 GHz) during approach, departure, and specifically on the non-illuminated hemispheres of Pluto and Charon during the respective intervals between occultation ingress and egress. We derive the brightness temperatures for these disk-resolved and unresolved observations. The mean values and 1σ deviations of brightness temperature for the unresolved sunlit disk are 33.2 ± 1.4 K and 47.2 ± 5.3 K for Pluto and Charon, respectively, consistent with the global albedos of the two bodies as well as with previous ground-based estimates at smaller wavelengths. A slightly colder temperature of 29.0 ± 2.5 K was determined for the disk-integrated nightside of Pluto and a larger drop in temperature was observed for Charon (40.9 ± 0.9 K), implying a smaller thermal inertia for Charon than Pluto. The measured brightness temperature of Pluto across the nightside diametric scan reached a maximum of 29.0 ± 1.5 K in the center of the disk. The profile shape is attributed to an emissivity effect, which favors thermal emission toward higher elevation angles. As a first approximation, the effective emissivity for thermal emission is calculated for the case when Pluto and Charon are uniformly smooth homogenous spheres. Under this assumption, the effective emissivity for these observations is close to unity for all probable surface constituents, implying that the effective temperature of the Pluto subsurface is only a few percent higher than the observed brightness temperature. A considerably lower subsurface emissivity is implied, however, if the higher atmospheric temperatures near the surface determined from the REX occultation measurements are also valid for the subsurface.
•Radio thermal emission of Pluto and Charon was measured at the wavelength λ = 4.17 cm during the New Horizons flyby in 2015.•Both dayside and nightside observations were recorded.•The brightness temperatures on the dayside are consistent with ground-based observations.•The nightside brightness temperatures of both Pluto and Charon are colder than on the dayside.•The brightness temperature of Pluto is higher than that of Charon, in agreement with their measured optical albedos.
The New Horizons Instrument Suite Fountain, Glen H; Weaver, Harold A; Reuter, Dennis C ...
Johns Hopkins APL technical digest,
01/2023, Letnik:
37, Številka:
1
Journal Article
Recenzirano
The New Horizons science payload consists of seven instruments-three optical instruments, two plasma instruments, a dust sensor, and a radio science receiver/radiometer. These instruments were ...designed to withstand the cold conditions and low light levels in the Kuiper Belt so they could investigate the global geology, surface composition and temperature, and the atmospheric pressure, temperature, and escape rate of Pluto and its moons. The same payload was used to explore Arrokoth, the most distant object ever targeted for a flyby. The instrument suite is highly power efficient and represents a degree of miniaturization that is unprecedented in planetary exploration. This article describes the instruments and how they met challenging mission requirements with resounding success, making groundbreaking measurements and returning data that continues to shed light on the mysterious planets and smaller bodies of the outer solar system.
The New Horizons spacecraft will achieve a wide range of measurement objectives at the Pluto system, including color and panchromatic maps, 1.25–2.50 micron spectral images for studying surface ...compositions, and measurements of Pluto’s atmosphere (temperatures, composition, hazes, and the escape rate). Additional measurement objectives include topography, surface temperatures, and the solar wind interaction. The fulfillment of these measurement objectives will broaden our understanding of the Pluto system, such as the origin of the Pluto system, the processes operating on the surface, the volatile transport cycle, and the energetics and chemistry of the atmosphere. The mission, payload, and strawman observing sequences have been designed to achieve the NASA-specified measurement objectives and maximize the science return. The planned observations at the Pluto system will extend our knowledge of other objects formed by giant impact (such as the Earth–moon), other objects formed in the outer solar system (such as comets and other icy dwarf planets), other bodies with surfaces in vapor-pressure equilibrium (such as Triton and Mars), and other bodies with N
2
:CH
4
atmospheres (such as Titan, Triton, and the early Earth).
PDF
