Structure and crustal balance of the Herald Arch and Hope Basin in the Chukchi Sea, Alaska

The Herald Arch is a structural high bounded by the Herald Thrust fault to the northeast and by a normal, or possibly strike-slip, fault to the southwest in the Chukchi Sea, off the northwest coast of Alaska. The thrust continues for approximately 60 kilometers from the northwest tip of the Lisburne Peninsula into the Chukchi Sea. Its dip varies from nearly 60 degrees in the east, to 20 degrees in the west before terminating on the available seismic data. Closer to the shore, the detachment of the Herald Thrust occurs at the edge of a Devonian rift basin containing the Franklinian Sequence. Moving towards the northwest, the rift diminishes along with the detachment of the Herald Thrust. Northeast of the Herald Thrust in the Colville Basin, the anticlines and thrust faults of the Brookian layers diminish in magnitude and displacement from the Lisburne Peninsula to the northwest. The depth to the reflection Moho decreases from approximately 37 km beneath the Colville Basin to 28 km under the Hope Basin to the south. Estimates for the amount of extension required to produce the present day crustal thickness are at least 20% less than the amount of Tertiary stretching that has been documented by restoration of supracrustal normal faults. The thinning of the crust could be attributed to differential spreading where the upper crust was stretched less then the lower crust and mantle, or due to and older, mid Cretaceous, extensional event that has gone unrecognized on the seismic data. A magnetic high that corresponds closely to the Herald Arch could be evidence of magmatic material brought up during the mid-Cretaceous spreading event

Maximizing the value of Solar System data through Planetary Spatial Data Infrastructures

Planetary spatial data returned by spacecraft, including images and higher-order products such as mosaics, controlled basemaps, and digital elevation models (DEMs), are of critical importance to NASA, its commercial partners and other space agencies. Planetary spatial data are an essential component of basic scientific research and sustained planetary exploration and operations. The Planetary Data System (PDS) is performing the essential job of archiving and serving these data, mostly in raw or calibrated form, with less support for higher-order, more ready-to-use products. However, many planetary spatial data remain not readily accessible to and/or usable by the general science user because particular skills and tools are necessary to process and interpret them from the raw initial state. There is a critical need for planetary spatial data to be more accessible and usable to researchers and stakeholders. A Planetary Spatial Data Infrastructure (PSDI) is a collection of data, tools, standards, policies, and the people that use and engage with them. A PSDI comprises an overarching support system for planetary spatial data. PSDIs (1) establish effective plans for data acquisition; (2) create and make available higher-order products; and (3) consider long-term planning for correct data acquisition, processing and serving (including funding). We recommend that Planetary Spatial Data Infrastructures be created for all bodies and key regions in the Solar System. NASA, with guidance from the planetary science community, should follow established data format standards to build foundational and framework products and use those to build and apply PDSIs to all bodies. Establishment of PSDIs is critical in the coming decade for several locations under active or imminent exploration, and for all others for future planning and current scientific analysis.Comment: 8 pages, 0 figures. White paper submitted to the Planetary Science and Astrobiology Decadal Survey 2023-203

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

Neptune Odyssey: A Flagship Concept for the Exploration of the Neptune–Triton System

The Neptune Odyssey mission concept is a Flagship-class orbiter and atmospheric probe to the Neptune-Triton system. This bold mission of exploration would orbit an ice-giant planet to study the planet, its rings, small satellites, space environment, and the planet-sized moon Triton. Triton is a captured dwarf planet from the Kuiper Belt, twin of Pluto, and likely ocean world. Odyssey addresses Neptune system-level science, with equal priorities placed on Neptune, its rings, moons, space environment, and Triton. Between Uranus and Neptune, the latter is unique in providing simultaneous access to both an ice giant and a Kuiper Belt dwarf planet. The spacecraft - in a class equivalent to the NASA/ESA/ASI Cassini spacecraft - would launch by 2031 on a Space Launch System or equivalent launch vehicle and utilize a Jupiter gravity assist for a 12 yr cruise to Neptune and a 4 yr prime orbital mission; alternatively a launch after 2031 would have a 16 yr direct-to-Neptune cruise phase. Our solution provides annual launch opportunities and allows for an easy upgrade to the shorter (12 yr) cruise. Odyssey would orbit Neptune retrograde (prograde with respect to Triton), using the moon's gravity to shape the orbital tour and allow coverage of Triton, Neptune, and the space environment. The atmospheric entry probe would descend in ~37 minutes to the 10 bar pressure level in Neptune's atmosphere just before Odyssey's orbit-insertion engine burn. Odyssey's mission would end by conducting a Cassini-like "Grand Finale,"passing inside the rings and ultimately taking a final great plunge into Neptune's atmosphere

Diurnal, Nonsynchronous Rotation and Obliquity Tidal Effects on Triton using a Viscoelastic Model: SatStressGUI. Implications for Ridge and Cycloid Formation

International audienceNeptune’s biggest moon Triton orbits at an almost constant distance of about 355,000 km from its parent body. The satellite has a very low eccentricity (e = 10-5), and rotates synchronously about Neptune. It is thought to have been differentiated enough for the formation of interior solid and even liquid layers [1]. Generally, diurnal tidal forcing is the main stressing mechanism a satellite with a sufficient eccentricity can experience. Other possibly combined sources participating in the tidal evolution of a satellite can be nonsynchronous rotation (NSR), axis tilt (obliquity), polar wander, and ice shell thickening. Given Triton’s current very low eccentricity, the induced diurnal tidal forcing must be relatively non existent. Triton’s eccentricity has most likely changed since its capture [2] and this change in eccentricity may account for the formation of surface features and maintaining a subsurface liquid ocean [2, 3]. Furthermore, obliquity induced tides have been shown to play a role in Triton’s recent geological activity [1] with its high inclination. Thus, modeling Triton’s tidal behavior is essential in order to constrain its interior structure, tidal stress magnitudes, and surface feature formation

The Implications of Tides on the Mimas Ocean Hypothesis

We investigate whether a present-day global ocean within Mimas is compatible with the lack of tectonic activity on its surface by computing tidal stresses for ocean-bearing interior structure models derived from observed librations. We find that, for the suite of compatible rheological models, peak surface tidal stresses caused by Mimas' high eccentricity would range from a factor of 2 smaller to an order of magnitude larger than those on tidally active Europa. Thermal stresses from a freezing ocean, or a past higher eccentricity, would enhance present-day tidal stresses, exceeding the magnitudes associated with Europa's ubiquitous tidally driven fractures and, in some cases, the failure strength of ice in laboratory studies. Therefore, in order for Mimas to have an ocean, its ice shell cannot fail at the stress values implied for Europa. Furthermore, if Mimas' ocean is freezing out, the ice shell must also be able to withstand thermal stresses that could be an order of magnitude higher than the failure strength of laboratory ice samples. In light of these challenges, we consider an ocean-free Mimas to be the most straightforward model, best supported by our tidal stress analysis

Modeling the Formation of Cycloids and Wavy Lineaments on Europa Resulting from Diurnal, Obliquity, and Nonsynchronous Rotation Stresses in a Visco-Elastic Ice Shell

International audienceJupiter’s icy moon Europa displays a variety of lineament types ranging from arcuate to “wavy” to cycloidal. These features can span 100s of km and reach heights of ~200 m. Here we explore how these features could evolve in a rotating diurnal stress field, with contributions from nonsynchronous rotation (NSR) and obliquity stresses. Previous work has invoked simulations of diurnal and added obliquity stress to explain Europa’s observed cycloidal lineaments. However, these models assumed an elastic ice shell, and neither of these two stress mechanisms alone can simulate Europa’s wavy lineaments. We expand on that previous elastic-shell modeling to demonstrate that diurnal tidal stresses can combine with NSR and obliquity stresses to create cycloidal lineaments or lineaments with a “wavy” planform, as simulated with the viscoelastic model SatStressGUI. If only diurnal tidal stress, or obliquity plus diurnal tidal stresses, are considered, then cycloidal lineaments are formed in response the changing magnitude and direction of the resultant principal stresses. The characteristics of the lineaments are controlled by a variety of parameters mainly propagation speed, ~1–5 m/s, thickness and viscosity of the lower ice layer, with a thicker and more viscous lower ice resulting in a smaller stress magnitude. For NSR, the magnitude of the simulated stress is chiefly dependent on the period of NSR and thickness and viscosity of the upper ice layer, such that a longer NSR period or a thicker ice shell with a low viscosity results in a smaller stress magnitude. When NSR stress is added and is similar in magnitude to the diurnal or obliquity stress, the simulated propagating lineaments can be wavy in planform shape. As the magnitude of the NSR stress is increased such that NSR stress dominates over diurnal and obliquity stress, the simulated lineaments are generally arcuate. We suggest that small amounts of NSR stress might have contributed to the formation of cycloids but that significant NSR was not necessary to account for their planform shape. But NSR may be an important contributing factor to the formation of the Europa’s wavy lineaments

Calculating Tidal Stresses on Satellites using SatStressGUI

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