Structure and Evolution of the Lunar Procellarum Region as Revealed by GRAIL Gravity Data

The Procellarum region is a broad area on the nearside of the Moon that is characterized by low elevations, thin crust, and high surface concentrations of the heat-producing elements uranium, thorium, and potassium. The Procellarum region has been interpreted as an ancient impact basin approximately 3200 km in diameter, though supporting evidence at the surface would have been largely obscured as a result of the great antiquity and poor preservation of any diagnostic features. Here we use data from the Gravity Recovery and Interior Laboratory (GRAIL) mission to examine the subsurface structure of Procellarum. The Bouguer gravity anomalies and gravity gradients reveal a pattern of narrow linear anomalies that border the Procellarum region and are interpreted to be the frozen remnants of lava-filled rifts and the underlying feeder dikes that served as the magma plumbing system for much of the nearside mare volcanism. The discontinuous surface structures that were earlier interpreted as remnants of an impact basin rim are shown in GRAIL data to be a part of this continuous set of quasi-rectangular border structures with angular intersections, contrary to the expected circular or elliptical shape of an impact basin. The spatial pattern of magmatic-tectonic structures bounding Procellarum is consistent with their formation in response to thermal stresses produced by the differential cooling of the province relative to its surroundings, coupled with magmatic activity driven by the elevated heat flux in the region

The NASA Roadmap to Ocean Worlds

In this article, we summarize the work of the NASA Outer Planets Assessment Group (OPAG) Roadmaps to Ocean Worlds (ROW) group. The aim of this group is to assemble the scientific framework that will guide the exploration of ocean worlds, and to identify and prioritize science objectives for ocean worlds over the next several decades. The overarching goal of an Ocean Worlds exploration program as defined by ROW is to identify ocean worlds, characterize their oceans, evaluate their habitability, search for life, and ultimately understand any life we find. The ROW team supports the creation of an exploration program that studies the full spectrum of ocean worlds, that is, not just the exploration of known ocean worlds such as Europa but candidate ocean worlds such as Triton as well. The ROW team finds that the confirmed ocean worlds Enceladus, Titan, and Europa are the highest priority bodies to target in the near term to address ROW goals. Triton is the highest priority candidate ocean world to target in the near term. A major finding of this study is that, to map out a coherent Ocean Worlds Program, significant input is required from studies here on Earth; rigorous Research and Analysis studies are called for to enable some future ocean worlds missions to be thoughtfully planned and undertaken. A second finding is that progress needs to be made in the area of collaborations between Earth ocean scientists and extraterrestrial ocean scientists

Top five elements on Pluto

The front of the graphic includes a picture of the planet, a histogram showing the abundance of the Top 5 elements at that planet, and an outline of the Periodic Table highlighting the location of those elements on the table. The back of the graphic features a biography of a planetary scientist who studies the planet and a short discussion written by the scientist of what makes that planet chemically unique in the solar system

Charon’s refractory factory

We combine novel laboratory experiments and exospheric modeling to reveal that “dynamic” Ly-α photolysis of Plutonian methane generates a photolytic refractory distribution on Charon that increases with latitude, consistent with poleward darkening observed in the New Horizons images. The flux ratio of the condensing methane to the interplanetary medium Ly-α photons, φ, controls the distribution and composition of Charon’s photoproducts. Mid-latitude regions are likely to host complex refractories emerging from low-φ photolysis, while high-φ photolysis at the polar zones primarily generate ethane. However, ethane being colorless does not contribute to the reddish polar hue. Solar wind radiolysis of Ly-α–cooked polar frost past spring sunrise may synthesize increasingly complex, redder refractories responsible for the unique albedo on this enigmatic moon

Bolometric Hemispherical Albedo Map of Pluto from New Horizons Observations

The New Horizons encounter with the Pluto system revealed Pluto to have an extremely spatially variable surface with expansive dark, bright, and intermediate terrains, refractory and volatile ices, and ongoing/recent endogenous and exogenous processes. Albedo is useful for understanding volatile transport because it quantifies absorbed solar energy; albedo may also provide insights into surface processes. Four filters of the New Horizons LORRI and MVIC imagers are used to approximate the bolometric (flux-weighted, wavelength-integrated) albedo. The bolometric hemispherical albedo (local energy balance albedo) as a function of the incidence angle of the solar illumination is measured for both Cthulhu and Sputnik Planitia, which are extensive, extreme dark and extreme bright terrains on Pluto. For both terrains, the bolometric hemispherical albedo increases by >30% from 0° to 90° incidence. The incidence-angle-average bolometric hemispherical albedo of Cthulhu is 0.12 ± 0.01, and that of Sputnik Planitia is 0.80 ± 0.06, where uncertainties are estimates based on scatter from different photometric functional approximations. The bolometric Bond albedo (global energy balance albedo) of Cthulhu is 0.12 ± 0.01, and that of Sputnik Planitia is 0.80 ± 0.07. A map of Pluto’s incidence-angle-average bolometric hemispherical albedo is produced. The incidence-angle-average bolometric hemispherical albedo, spatially averaged over areas north of ≈30° S, is ≈0.54. Pluto has three general albedo categories: (1) very low albedo southern equatorial terrains, including Cthulhu; (2) high-albedo terrains, which constitute most of Pluto’s surface; and (3) very high albedo terrains, including Sputnik Planitia. Pluto’s extraordinary albedo variability with location is also spatially sharp at some places