The New Horizons spacecraft has found evidence for geologic activity on the surface of Pluto, including extensional tectonic deformation of its water ice bedrock (see Moore et al., 2016). One mechanism that could drive extensional tectonic activity is global surface expansion due to the partial freezing of an ocean. We use updated physical properties for Pluto and simulate its thermal evolution to understand the survival of a possible subsurface ocean. For thermal conductivities of rock less than 3 W m$^{-1}$ K$^{-1}$, an ocean forms and at least partially freezes, leading to recent extensional stresses in the ice shell. In scenarios where the ocean freezes and the ice shell is thicker than $260$ km, ice II forms and causes global volume contraction. Since there is no evidence for recent compressional tectonic features, we argue that ice II has not formed and that Pluto's ocean has likely survived to present day.
Pluto's surface is geologically complex because of volatile ices that are mobile on seasonal and longer time scales. Here we analyzed New Horizons LEISA spectral data to globally map the nitrogen ice, including nitrogen with methane diluted in it. Our goal was to learn about the seasonal processes influencing ice redistribution, to calculate the globally averaged energy balance, and to place a lower limit on Pluto's N2 inventory. We present the average latitudinal distribution of nitrogen and investigate the relationship between its distribution and topography on Pluto by using maps that inclu…
Sputnik Planitia, Pluto's gigantic ice glacier, hosts numerous scientific mysteries, including the presence of thousands of elongated pit structures. We examine various attributes of these pit structures in New Horizons data sets, revealing their length, aspect ratios, and orientation properties; we also study their interior reflectivities, colors, and compositions, and compare these attributes to some other relevant regions on Pluto. We then comment on origin mechanisms of the pits and also the fate of the missing volatiles represented by the pits on Sputnik Planitia.
We present a coupled reorientation and climate model, to understand how true polar wander (TPW) and atmospheric condensation worked together to create the Sputnik Planitia (SP) ice sheet and reorient it to its present-day location on Pluto. SP is located at 18 N, 178 E, very close to the anti-Charon point, and it has been previously shown that this location can be explained by TPW reorientation of an impact basin as it fills with N2 ice. We readdress that hypothesis while including a more accurate treatment of Pluto's climate and orbital obliquity cycle. Our model again finds that TPW is a via…
The origin of the interstellar object 1I/'Oumuamua has defied explanation. We perform calculations of the non-gravitational acceleration that would be experienced by bodies composed of a range of different ices and demonstrate that a body composed of N2 ice would satisfy the available constraints on the non-gravitational acceleration, size and albedo, and lack of detectable emission of CO or CO2 or dust. We find that 'Oumuamua was small, with dimensions 45 m x 44 m x 7.5 m at the time of observation at 1.42 au from the Sun, with a high albedo of 0.64. This albedo is consistent with the N2 surf…
The origin of the interstellar object 1I/'Oumuamua, has defied explanation. In a companion paper (Jackson & Desch, 2021), we show that a body of N2 ice with axes 45 m x 44 m x 7.5 m at the time of observation would be consistent with its albedo, non-gravitational acceleration, and lack of observed CO or CO2 or dust. Here we demonstrate that impacts on the surfaces of Pluto-like Kuiper belt objects (KBOs) would have generated and ejected ~10^14 collisional fragments--roughly half of them H2O ice fragments and half of them N2 ice fragments--due to the dynamical instability that depleted the prim…
Pluto's landscape is shaped by the cycles of the volatile ices covering its surface. In particular, the Sputnik Planitia (SP) ice sheet displays a large diversity of terrains, with bright and dark plains, pits, topographic depressions and evidences of recent and past glacial flows. Outside SP, New Horizons also revealed numerous N2 ice deposits, in Tombaugh Regio and at mid-northern latitudes. These observations suggest a complex history involving volatile and glacial processes on different timescales. We present numerical simulations of volatile transport on Pluto performed with a model able …
The vast, deep, volatile-ice-filled basin informally named Sputnik Planum is central to Pluto's geological activity[1,2]. Composed of molecular nitrogen, methane, and carbon monoxide ices[3], but dominated by N2-ice, this ice layer is organized into cells or polygons, typically ~10-40 km across, that resemble the surface manifestation of solid state convection[1,2]. Here we report, based on available rheological measurements[4], that solid layers of N2 ice approximately greater than 1 km thick should convect for estimated present-day heat flow conditions on Pluto. More importantly, we show num…
New Horizons observations suggest that CH4 on Pluto has a complex history, involving reservoirs of different composition, thickness and stability controlled by volatile processes occurring on different timescales. In order to interpret these observations, we use a Pluto volatile transport model able to simulate the cycles of N2 and CH4 ices over millions of years. By assuming fixed solid mixing ratios, we explore how changes in surface albedos, emissivities and thermal inertias impact volatile transport. This work is therefore a direct and natural continuation of the work by Bertrand et al. (2…
Evidence for possible N2 basal flow beneath Pluto northern Sputnik Planitia
Southwest Research Institute（西南研究所）；SETI Institute at NASA Ames Research Center（NASA阿姆斯研究中心SETI研究所）；INSTAAR, University of Colorado（科罗拉多大学INSTAAR）；Department of Geological Sciences and INSTAAR University of Colorado Boulder（科罗拉多大学博尔德分校地质科学系及INSTAAR）；Planetary Science Institute（行星科学研究所）
The New Horizons spacecraft mapped colors and infrared spectra across the encounter hemispheres of Pluto and Charon. The volatile ices CH$_4$, CO, and N$_2$, that dominate Pluto's surface, have complicated spatial distributions resulting from sublimation, condensation, and glacial flow acting over seasonal and geological timescales. Pluto's H$_2$O ice "bedrock" is also mapped, with isolated outcrops occurring in a variety of settings. Pluto's surface exhibits complex regional color diversity associated with its distinct provinces. Charon's color pattern is simpler, dominated by neutral low lat…
Systematic geomorphological mapping and detailed landform analysis using the highest resolution images obtained by the New Horizons spacecraft reveal the presence of a range of differentiable terrains on Charon, the largest moon of Pluto, that were not examined in detail by the early studies. The most important findings of our work include (1) truncation and omission of large craters (diameters > 30-40 km) and their crater rim ridges along the eastern edges of several north-trending, eastward-convex, arcuate ranges in Oz Terra, (2) lobate ridges, lobate knob trains, and lobate aprons resemblin…
On July 14th 2015, NASA's New Horizons mission gave us an unprecedented detailed view of the Pluto system. The complex compositional diversity of Pluto's encounter hemisphere was revealed by the Ralph/LEISA infrared spectrometer on board of New Horizons. We present compositional maps of Pluto defining the spatial distribution of the abundance and textural properties of the volatiles methane and nitrogen ices and non-volatiles water ice and tholin. These results are obtained by applying a pixel-by-pixel Hapke radiative transfer model to the LEISA scans. Our analysis focuses mainly on the large …
Under both engineering and natural conditions on Earth and in the Universe, some gas hydrates are found to be stabilised outside their window of thermodynamic stability by the formation of an ice layer-a phenomenon termed self-preservation. Low occupancy surface regions on type I CO2 clathrate structures together with the self-preserving ice layer lead to an effective buoyancy for these structures which restricts the size range of particles that float in the ocean on Enceladus, Pluto and similar oceanic worlds. Our goal here is to investigate the implications of Lifshitz forces and low occupan…
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 $\approx$10 Ma. Surrounding terrains show active glacial flow, apparent transport and rotation of large buoyant water-ice crustal blocks, and pitting, likely by sublimation erosion and/or collapse. More enigmatic features include tall mounds with central depressions that are …
Observations of Pluto's surface made by the New Horizons spacecraft indicates present-day nitrogen ice glaciation in and around the basin known as Sputnik Planum. Motivated by these observations, we have developed an evolutionary glacial flow model of solid nitrogen ice taking into account its published thermophysical and rheologies properties. This model assumes that glacial ice layers flow laminarly and have low aspect ratios which permits a vertically integrated mathematical formulation. We assess the conditions for the validity of laminar nitrogen ice motion by revisiting the problem of th…
We discuss in a thermodynamic, geologically empirical way the long-term nature of the stable majority ices that could be present in Kuiper Belt Object 2014 MU69 after its 4.6 Gyr residence in the EKB as a cold classical object. Considering the stability versus sublimation into vacuum for the suite of ices commonly found on comets, Centaurs, and KBOs at the average ~40K sunlit surface temperature of MU69 over Myr to Gyr, we find only 3 common ices that are truly refractory: HCN, CH3OH, and H2O (in order of increasing stability). NH3 and H2CO ices are marginally stable and may be removed by any …
The presence of N2 in the surface environment of Pluto is critical in creating Pluto's richness of features and processes. Here, we propose that the nitrogen atoms in the N2 observed on Pluto were accreted in that chemical form during the formation of Pluto. We use New Horizons data and models to estimate the amounts of N2 in the following exterior reservoirs: atmosphere, escape, photochemistry, and surface. The total exterior inventory is deduced to be dominated by a glacial sheet of N2-rich ices at Sputnik Planitia, or by atmospheric escape if past rates of escape were much faster than at pr…
Existence of subsurface oceans on the satellites of the giant planets and Trans-Neptunian objects has been predicted for some time. Oceans on icy worlds exert a considerable influence on the dynamics of the ice-ocean system and, because of the astrobiological potential, represent an important objective for future missions. The Pluto-Charon system is representative of an icy moon orbiting a dwarf planet formed from the remnants of a giant impact. Evolution of icy moons is primarily controlled by the mode and efficiency of heat transfer through the outer ice shell, which is influenced by the pre…
The exploration of the Pluto-Charon system by the New Horizons spacecraft represents the first opportunity to understand the distribution of albedo and other photometric properties of the surfaces of objects in the Solar System's "Third Zone" of distant ice-rich bodies. Images of the entire illuminated surface of Pluto and Charon obtained by the Long Range Reconnaissance Imager (LORRI) camera provide a global map of Pluto that reveals surface albedo variegations larger than any other Solar System world except for Saturn's moon Iapetus. Normal reflectances on Pluto range from 0.08-1.0, and the …
Neptune's moon Triton shares many similarities with Pluto, including volatile cycles of N2, CH4 and CO, and represents a benchmark case for the study of surface-atmosphere interactions on volatile-rich KBOs. Within the context of New Horizons observations of Pluto as well as recent Earth-based observations of Triton, we adapt a Plutonian VTM to Triton, and test its ability to simulate its volatile cycles, thereby aiding our understanding of its climate. We present VTM simulations exploring the volatile cycles on Triton over long-term and seasonal timescales for varying model parameters. We exp…
Pluto's atmospheric haze settles out rapidly compared with geological timescales. It needs to be accounted for as a surface material, distinct from Pluto's icy bedrock and from the volatile ices that migrate via sublimation and condensation on seasonal timescales. This paper explores how a steady supply of atmospheric haze might affect three distinct provinces on Pluto. We pose the question of why they each look so different from one another if the same haze material is settling out onto all of them. Cthulhu is a more ancient region with comparatively little present-day geological activity, wh…
The deep nitrogen-covered Sputnik Planitia (SP; informal name) basin on Pluto is located very close to the longitude of Pluto's tidal axis[1] and may be an impact feature [2], by analogy with other large basins in the solar system[3,4]. Reorientation[5-7] due to tidal and rotational torques can explain SP's location, but requires it to be a positive gravity anomaly[7], despite its negative topography. Here we argue that if SP formed via impact and if Pluto possesses a subsurface ocean, a positive gravity anomaly would naturally result because of shell thinning and ocean uplift, followed by lat…
Results are presented from a 3-D Pluto general circulation model (GCM) that includes conductive heating and cooling, non-local thermodynamic equilibrium (non-LTE) heating by methane at 2.3 and 3.3 microns, non-LTE cooling by cooling by methane at 7.6 microns, and LTE CO rotational line cooling. The GCM also includes a treatment of the subsurface temperature and surface-atmosphere mass exchange. An initially 1 m thick layer of surface nitrogen frost was assumed such that it was large enough to act as a large heat sink (compared with the solar heating term) but small enough that the water ice su…
Pluto has a heterogeneous surface, despite a global haze deposition rate of ~1 micrometer per orbit (Cheng et al., 2017; Grundy et al., 2018). While there could be spatial variation in the deposition rate, this has not yet been rigorously quantified, and naively the haze should coat the surface more uniformly than was observed. One way (among many) to explain this contradiction is for atmospheric pressure at the surface to drop low enough to interrupt haze production and stop the deposition of particles onto part of the surface, driving heterogeneity. If the surface pressure drops to less than…
Changes in Pluto's Atmosphere Based on Stellar Occultation Data from 2017 to 2023
Planetary Science Institute（行星科学研究所）；Massachusetts Institute of Technology（麻省理工学院）；Lowell Observatory（洛厄尔天文台）；Universität Stuttgart（斯图加特大学）；SOFIA Science Center NASA Ames Research Center（NASA艾姆斯研究中心索菲亚科学中心）；Las Cumbres Observatory（拉斯孔布雷斯天文台）
Terrestrial planets covered globally with thick oceans (termed ocean planets) in the habitable zone were previously inferred to have extremely hot climates in most cases. This is because ${\rm H_2O}$ high-pressure (HP) ice on the seafloor prevents chemical weathering and, thus, removal of atmospheric CO$_2$. Previous studies, however, ignored melting of the HP ice and horizontal variation in heat flux from oceanic crusts. Here we examine whether high heat fluxes near the mid-ocean ridge melts the HP ice and thereby removes atmospheric ${\rm CO_2}$. We develop integrated climate models of an Ea…
One of the clearest but unresolved questions for Europa is the thickness of its icy shell. Europa's surface is resplendent with geological features that bear on this question, and ultimately on its interior, geological history, and astrobiological potential. We characterize the size and topographic expression of circular and subcircular features created by endogenic thermal and tectonic disturbances on Europa: pits, uplifts, and small, subcircular chaos. We utilize the medium-resolution Galileo regional maps (RegMaps), as well as high-resolution regions, digital elevation models derived from a…
An unidentified absorption feature at 5.11 $μ$m on the surface of Titan and Pluto from JWST spectroscopy
Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité（巴黎天文台，巴黎文理研究大学，法国国家科学研究中心，索邦大学，巴黎西岱大学）；California Institute of Technology（加州理工学院）；Jet Propulsion Laboratory, California Institute of Technology（喷气推进实验室，加州理工学院）；Université Grenoble Alpes, CNRS, IPAG（格勒诺布尔阿尔卑斯大学，法国国家科学研究中心，IPAG）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；University of Bristol（布里斯托大学）；Université de Reims Champagne-Ardenne, CNRS（兰斯香槟-阿登大学，法国国家科学研究中心）；Université Paris Cité, Institut de Physique du Globe de Paris (IPGP), CNRS（巴黎西岱大学，巴黎地球物理研究所，法国国家科学研究中心）；CNRM, Météo-France, CNRS, Université de Toulouse（区域气候研究与应用中心，法国气象局，法国国家科学研究中心，图卢兹大学）
Infrared Spectra and Optical Constants of Astronomical Ices: II. Ethane and Ethylene
红外光谱观测已经确定了冥王星和其他TNO上存在碳氢化合物冰，但如果没有准确的光学常数（n，k）和参考光谱，就无法推断出这些分子的丰度。在本文中，我们提出了我们最近的测量乙烷（C $_2$ H $_6$）和乙烯（C $_2$ H $_4$）在多个冰相和在多个温度下的近红外和中红外光学常数。在我们最近的工作乙炔（C $_2$ H $_2$），我们还报告了新的测量每个冰在670 nm的折射率。在可能的情况下，与早期的工作进行比较，并提供我们新结果的电子版本。
Context. Pluto's tenuous nitrogen (N2) atmosphere undergoes strong seasonal effects due to high obliquity and orbital eccentricity, and has been recently (July 2015) observed by the New Horizons spacecraft. Goals are (i) construct a well calibrated record of the seasonal evolution of surface pressure on Pluto and (ii) constrain the structure of the lower atmosphere using a central flash observed in 2015. Method: eleven stellar occultations by Pluto observed between 2002 and 2016 are used to retrieve atmospheric profiles (density, pressure, temperature) between $\sim$5 km and $\sim$380 km altit…
Seismic data will be a vital geophysical constraint on internal structure of Europa if we land instruments on the surface. Quantifying expected seismic activity on Europa both in terms of large, recognizable signals and ambient background noise is important for understanding dynamics of the moon, as well as interpretation of potential future data. Seismic energy sources will likely include cracking in the ice shell and turbulent motion in the oceans. We define a range of models of seismic activity in Europa's ice shell by assuming each model follows a Gutenberg-Richter relationship with varyin…
University of Arkansas（阿肯色大学）；SETI Institute（SETI研究所）；NASA Goddard Space Flight Center（美国国家航空航天局戈达德太空飞行中心）；University of Central Florida（中佛罗里达大学）；NASA Jet Propulsion Laboratory, California Institute of Technology（美国国家航空航天局喷气推进实验室，加州理工学院）
We map the surface of Pluto using an unsupervised machine learning technique using the near-infrared observations of the LEISA/Ralph instrument onboard NASA's New Horizons spacecraft. The principal component reduced Gaussian mixture model was implemented to investigate the geographic distribution of the surface units across the dwarf planet. We also present the likelihood of each surface unit at the image pixel level. Average I/F spectra of each unit were analyzed -- in terms of the position and strengths of absorption bands of abundant volatiles such as N${}_{2}$, CH${}_{4}$, and CO and nonvo…
Ice-covered ocean worlds possess diverse energy sources and associated mechanisms that are capable of driving significant seismic activity, but to date no measurements of their seismic activity have been obtained. Such investigations could probe their transport properties and radial structures, with possibilities for locating and characterizing trapped liquids that may host life and yielding critical constraints on redox fluxes, and thus on habitability. Modeling efforts have examined seismic sources from tectonic fracturing and impacts. Here, we describe other possible seismic sources, their …
