In a previous article, I briefly described one of five new studies that have been conducted since the historic flyby of Pluto by New Horizons on 14 July of last year. In that article, I discuss a new but not surprising confirmation of methane snow on Pluto’s surface. In a brief, related article I describe newly-discovered features of Pluto’s north polar region. Additional studies will be forthcoming as the remaining data from New Horizons is downlinked and analyzed.
The five studies are presented together as a compendium, described by the team as
New Horizons unveils the Pluto system
In July 2015, the New Horizons spacecraft flew through the Pluto system at high speed, humanity’s first close look at this enigmatic system on the outskirts of our solar system. In a series of papers, the New Horizons team present their analysis of the encounter data downloaded so far: Moore et al. present the complex surface features and geology of Pluto and its large moon Charon, including evidence of tectonics, glacial flow, and possible cryovolcanoes. Grundy et al. analyzed the colors and chemical compositions of their surfaces, with ices of H2O, CH4, CO, N2, and NH3 and a reddish material which may be tholins. Gladstone et al. investigated the atmosphere of Pluto, which is colder and more compact than expected and hosts numerous extensive layers of haze. Weaver et al. examined the small moons Styx, Nix, Kerberos, and Hydra, which are irregularly shaped, fast-rotating, and have bright surfaces. Bagenal et al. report how Pluto modifies its space environment, including interactions with the solar wind and a lack of dust in the system. Together, these findings massively increase our understanding of the bodies in the outer solar system. They will underpin the analysis of New Horizons data, which will continue for years to come.
The topics of the five studies include:
- The Geology of Pluto and Charon through the eyes of New Horizons. In this study, the enigmatic geologies of Pluto and its largest satellite, Charon, are presented in depth. An excerpt from the study’s abstract follows
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.
- Surface compositions across Pluto and Charon. This is the study I described in a previous article. In addition to discussing the varying albedos of Pluto’s frozen terrain, it describes in detail the surface compositions of Pluto and Charon, attributing the deep-red coloration of Pluto’s Cthulhu Regio to the presence of tholins (complex molecules that form when methane is exposed to sunlight). An excerpt from the study’s abstract follows
The New Horizons spacecraft mapped colors and infrared spectra across the encounter hemispheres of Pluto and Charon. The volatile methane, carbon monoxide, and nitrogen ices that dominate Pluto’s surface have complicated spatial distributions resulting from sublimation, condensation, and glacial flow acting over seasonal and geological time scales. Pluto’s water ice “bedrock” was 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 latitudes and a reddish northern polar region. Charon’s near-infrared spectra reveal highly localized areas with strong ammonia absorption tied to small craters with relatively fresh-appearing impact ejecta.
- Pluto’s interaction with its space environment: Solar wind, energetic particles, and dust.
This article describes the Pluto near-space environment or the proximate environment above the planet’s surface. Particular attention is given to the magnitude of the solar wind flux and its interaction with the planet’s tenuous atmosphere. An excerpt from the study’s abstract follows
The New Horizons spacecraft carried three instruments that measured the space environment near Pluto as it flew by on 14 July 2015. The Solar Wind Around Pluto (SWAP) instrument revealed an interaction region confined sunward of Pluto to within about 6 Pluto radii. The region’s surprisingly small size is consistent with a reduced atmospheric escape rate, as well as a particularly high solar wind flux. Observations from the Pluto Energetic Particle Spectrometer Science Investigation (PEPSSI) instrument suggest that ions are accelerated and/or deflected around Pluto.
- The atmosphere of Pluto as observed by New Horizons.
In a separate study from the previous, a detailed analysis of the state of the planet’s atmosphere is presented. Particular attention is given to the atmosphere’s stratified haze layers, at least 20 in total. An excerpt from the study’s abstract follows
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 small satellites of Pluto as observed by New Horizons.
Conducted separately from Charon, Pluto’s principal moon, a study of Pluto’s four minor moons, Styx, Nix, Kerberos and Hydra is presented. Of particular note is the determination of their age; with crater densities suggesting an ancient surface for Nix and Hydra of over 4 billion years, a time that predates the Late Heavy Bombardment period, their formation is believed to date back to the very beginning of the solar system. All four moons present with relatively high albedos ranging from 0.5 to 0.9, a determination strongly suggestive of a water-ice covering or surface composition. An excerpt from the study’s abstract follows
The New Horizons mission has provided resolved measurements of Pluto’s moons Styx, Nix, Kerberos, and Hydra. All four are small, with equivalent spherical diameters of ~40 kilometers for Nix and Hydra and ~10 kilometers for Styx and Kerberos. They are also highly elongated, with maximum to minimum axis ratios of ~2. All four moons have high albedos (~50 to 90%) suggestive of a water-ice surface composition. Crater densities on Nix and Hydra imply surface ages of at least 4 billion years.
Imagination is more important than knowledge
An index of all articles in this blog can be found here.