The topography of ocean worlds is often used to infer ice shell thicknesses by assuming topography is compensated by a basal root. We systematically test the stability of isostatically compensated ...topography in ice shells. At short horizontal wavelengths, lithospheric strength can support surface topography, while at long wavelengths, buoyancy forces can support topography at the surface and base of the ice shell over geologic time scales. These behaviors are also seen for Airy isostasy in terrestrial worlds. Contrastingly at intermediate scales, the mechanically weak lower ice shell can inhibit the transfer of buoyancy forces to the surface. Factors such as surface temperature can alter the contribution of lithospheric strength, decreasing the stability of a compensating root. This nuanced understanding of icy shell lithospheres provides crucial insights for interpreting surface features and inferring underlying ice shell thickness, with substantial relevance for upcoming space missions to the Jovian system.
Plain Language Summary
Ocean moons have topography on their surfaces that can be used to estimate the thickness of the capping ice shells. In contrast to rocky worlds, the nature of ice shells prevents traditional approaches from being applied. In this study, we use geophysical models to simulate how topography evolves over geologic time. For small features, the stiffness of the ice crust plays a significant role in supporting topography. For larger features, buoyancy forces, like how an iceberg floats, keep topography stable over long periods. In the lower shell near the underlying ocean, the ice is near its melting temperature, which makes it much weaker than the ice nearer the surface. This weakness can prevent the buoyancy forces from reaching the surface for intermediate scale features. Understanding the dynamics of Airy isostasy in ocean worlds can help interpret data collected from space missions, and further our understanding of these icy satellites.
Key Points
Distinct behaviors emerge in support of icy shell topography at varying spatial scales
Ice shell thickness estimates using Airy isostasy are valid at only long wavelengths
Coronae are quasi‐circular volcano‐tectonic features on Venus. Four critical observations have been identified within the coronae population, including fracture annuli, a wide range of diameters, ...complex and varied topography, and various types of associated volcanic features. Geophysical models have attempted to replicate their formation from a variety of lithospheric processes but struggle to recreate all four of the critical observations. Volcanism is an often overlooked characteristic in corona formation models. Paleotopographic techniques are applied to lava flows associated with Atete Corona and Aruru Corona in the Beta‐Atla‐Themis region to investigate post‐emplacement changes in topography. Our results indicate marked divergence between lava flow orientation and the modern slope within the fracture annuli of the coronae. Intra‐annular flows at Atete Corona were emplaced on a surface that was reoriented by up to ∼180°. Intra‐annular flows at Aruru Corona were emplaced on a surface that was reoriented between 90° and 145°. Lava flows on the flanks of both coronae diverge less than those within the fractures. This finding suggests a progression of volcanism that starts at the interior of the corona and migrates outward to the fracture annuli. The role of volcanism, both intrusive and extrusive, is likely to play a more substantial role in the corona formation. Incorporating melt migration into geophysical models could significantly enhance our comprehension of the processes underlying the formation of coronae.
Plain Language Summary
Coronae are circular structures found only on the surface of Venus with characteristics of both volcanoes and tectonically formed features. There are four key observations have been identified about these structures: they are surrounded by a circle of fractures, they come in a wide range of sizes, they vary in the shape of their topography, and they are often associated with volcanic activity. Current models that attempt to explain their formation through processes within Venus' outer shell (or lithosphere) have difficulty accounting for all these observations. In this study, lava flows related to two coronae, Atete Corona and Aruru Corona, are examined using techniques that provide information on how the surface changes over time. Our results show that there is a significant mismatch between the direction of the lava flows and the slopes they are on top of. In some places, the lava flows appeared to have “flowed” uphill. Additionally, the differences between flows near the coronae centers and the modern slopes are greater than those at the edges of the coronae, indicating that volcanic activity started from the coronae interiors and moved outward. These findings suggest a crucial role for both surface and subsurface volcanism in the coronae formation.
Key Points
Geophysical models of corona formation struggle to recreate critical observations and underestimate the role of volcanism
Lava flows associated with Atete and Aruru Corona are not aligned with modern downslope directions and show migrating volcanic centers
The role of volcanism is likely to play a more substantial role in corona formation and may help explain their diverse morphologies
•The viscoelastic deformation of Mead basin is simulated.•The background heat flow of Venus in the vicinity of Mead basin is estimated.•The rheology of Venus's interior is assessed and appears to be ...dry.
Mead, the largest crater on Venus, has low topographic relief at the surface and at the crust-mantle boundary. Due to high surface temperatures, viscous deformation could play an important role in crustal structure. Using the finite element method, we simulate the long-term viscoelastic deformation of Mead crater and investigate the role of lower crustal flow in the evolution of the surface and subsurface topography. We examine the thermal states that allow this evolution to occur and determine the background heat flux. Our study constrains the background heat flux in the vicinity of Mead basin to 55–90mWm−2. This surface heat flow is generally higher than the average Venusian global values suggested by recent thermal models. In addition by applying hydrous and anhydrous creep rheological parameters, we demonstrate that the Venus's interior is rheologically dry and that the crust near Mead could be relatively high in plagioclase.
Thank You to Our 2023 Peer Reviewers Rajaram, Harihar; Aiyyer, Anantha; Camargo, Suzana ...
Geophysical research letters,
16 May 2024, Letnik:
51, Številka:
9
Journal Article
Recenzirano
Odprti dostop
On behalf of the journal, AGU, and the scientific community, the editors of Geophysical Research Letters would like to sincerely thank those who reviewed manuscripts for us in 2023. The hours reading ...and commenting on manuscripts not only improve the manuscripts, but also increase the scientific rigor of future research in the field. With the advent of AGU's data policy, many reviewers have also helped immensely to evaluate the accessibility and availability of data, and many have provided insightful comments that helped to improve the data presentation and quality. We greatly appreciate the assistance of the reviewers in advancing open science, which is a key objective of AGU's data policy. We particularly appreciate the timely reviews in light of the demands imposed by the rapid review process at Geophysical Research Letters. We received 4,512 submissions in 2023 and 5,112 reviewers contributed to their evaluation by providing 8,587 reviews in total. We deeply appreciate their contributions.
Plain Language Summary
Individuals in italics provided three or more reviews for GRL in 2023.
Key Points
The editors thank the 2023 peer‐reviewers
The primary objective of the Europa Clipper mission is to assess the habitability of Europa, an overarching goal that rests on improving our understanding of Europa’s interior structure, composition, ...and geologic activity. Here we describe the Gravity and Radio Science (G/RS) investigation. The primary measurement, the gravitational tidal Love number
k
2
, will be an independent diagnostic of the presence of a global subsurface ocean, but G/RS will make a number of other key measurements related to Europa’s deep interior, silicate mantle-ocean interface, ice shell, ionosphere, and plasma environment. Although radio science is common to many missions, Europa Clipper’s orbit and spacecraft configuration during flybys present special challenges for the design of this experiment. The information obtained through G/RS will be complementary to the measurements by the other instruments onboard Europa Clipper, and their combined analysis will refine the geophysical understanding of Europa necessary to best assess its potential habitability.
Thank You to Our 2022 Peer Reviewers Rajaram, Harihar; Camargo, Suzana; Cappa, Christopher D. ...
Geophysical research letters,
16 May 2023, Letnik:
50, Številka:
9
Journal Article
Recenzirano
Odprti dostop
On behalf of the journal, AGU, and the scientific community, the editors of Geophysical Research Letters would like to sincerely thank those who reviewed manuscripts for us in 2022. The hours reading ...and commenting on manuscripts not only improve the manuscripts, but also increase the scientific rigor of future research in the field. With the advent of AGU's data policy, many reviewers have also helped immensely to evaluate the accessibility and availability of data, and many have provided insightful comments that helped to improve the data presentation and quality. We greatly appreciate the assistance of the reviewers in advancing open science, which is a key objective of AGU's data policy. We particularly appreciate the timely reviews in light of the demands imposed by the rapid review process at Geophysical Research Letters. We received 6,687 submissions in 2022 and 5,247 reviewers contributed to their evaluation by providing 8,720 reviews in total. We deeply appreciate their contributions in these challenging times.
Plain Language Summary
Individuals in italics provided three or more reviews for GRL in 2022.
Key Points
The editors thank the 2022 peer reviewers
•Stereo topography is used to measure crater morphologies on Dione and Tethys.•Relaxation affects craters across a large diameter range on Dione and Tethys.•Heat flows >60mWm−2 are needed to relax ...several craters on both satellites.•Similar resonance-induced tidal heating may have affected Enceladus and Dione.•Odysseus impact on Tethys limits assessment of relaxation across its surface.
Relating relaxation of impact crater topography to past heat flow through the crusts of icy satellites is a technique that has been applied to satellites around Jupiter and Saturn. We use global digital elevation models of the surfaces of Dione and Tethys generated from Cassini data to obtain crater depth/diameter (d/D) data. Relaxation is found to affect craters down to smaller diameters on these satellites compared to Rhea. We perform relaxation simulations in order to assess the heat flow necessary to relax craters on Dione and Tethys to their present morphologies. Heat flows exceeding 60mWm−2 are required to relax several craters on both satellites, and relaxation appears to be subject to geographical controls. On Dione, we define a ‘relaxation dichotomy’ that separates the more relaxed craters in sparsely cratered plains from the less relaxed craters in heavily cratered terrain. The configuration of this dichotomy resembles that of the structural-geological dichotomy on Enceladus, implying that a similar resonance-induced tidal heating mechanism concentrated in the southern hemisphere may have affected both satellites. Defining geographical distribution of relaxation on Tethys is hindered by the presence of the young Odysseus impact and its associated ejecta.
Pluto's polygons explained Dombard, Andrew J; O'Hara, Sean
Nature,
06/2016, Letnik:
534, Številka:
7605
Journal Article
Recenzirano
Odprti dostop
The Sputnik Planum basin of Pluto contains a sheet of nitrogen ice, the surface of which is divided into irregular polygons tens of kilometres across. Two studies reveal that vigorous convection ...causes these polygons. See Letters (https://www.nature.com/articles/nature18016) & (https://www.nature.com/articles/nature18289)
Venus boasts an abundance of volcanoes and volcano‐like structures. Synthetic aperture radar images of the surface have revealed extensive evidence of volcanism, including lava flows and edifices. ...Volcanic activity is further supported by crater statistics, and analysis of topography and gravity data. Unique to Venus, coronae are quasi‐circular volcano‐tectonic features exhibiting diverse volcanic characteristics. Despite this, volcanism is often under‐represented in formation models. We identify a new subset of coronae that display topographic changes subsequent to the emplacement of lava flows within their fracture annuli, pointing to the critical role of volcanic and magmatic processes in the formation of these coronae. Through spherical‐harmonic distribution analysis, we find that this new subset is spatially related to the full coronae database, pointing to an intrinsic process of coronae formation. Furthermore, coronae exhibit strong correlations and similar spectral shapes at low spherical harmonic degrees with large volcanoes, suggesting a shared geodynamic origin. Our findings underscore the pivotal role of volcanism in coronae formation and highlight the need for future research to integrate magmatic and volcanic processes more comprehensively into geophysical models. Such models would better capture the complex interactions between volcanic emplacement, magmatic activity, and lithospheric dynamics on Venus.
Plain Language Summary
Venus's surface has a large number of volcanoes and features with characteristics similar to volcanoes. Radar imagery of the surface reveals signs of volcanism such as lava flows and volcanically built mountains. A unique volcanic feature, found only on Venus, are coronae, which have circular fractures and various types of associated volcanic activity. Explanations of how coronae form often do not consider the role of volcanic activity. In our study, we identify a new group of coronae that have undergone changes in topography after lava erupted and flowed over them, which has been interpreted as volcanism having a central role in corona formation. The locations of this subset of coronae on the surface fit well with all other coronae, suggesting that the processes that caused this topographic change occur throughout the corona population and are a basic part of how all coronae form. Additionally, we find that coronae have a similar pattern on the surface to large volcanoes, which indicates a shared volcanically based origin. Our work shows that in order to better understand coronae, we need to consider the role of volcanism in their formation.
Key Points
A new subset of coronae shows topographic changes post‐lava flow emplacement
Spectral analysis reveals strong long‐wavelength similarities between coronae and large volcanoes
Volcanism plays a crucial role in corona formation and should be considered central in future models of formation
