Pub Date : 2024-12-17DOI: 10.1016/j.icarus.2024.116440
A.E. Zubarev, I.E. Nadezhdina
Saturn's odd-shaped satellite Hyperion is unique in its chaotic rotation. Owing to limited observational data, there is currently no functional model describing the object's changing orientation in space, commonly agreed upon. Consequently, there is also no established body-fixed reference frame, critical for the creation of mapping products. Using best 166 images obtained until the end of the Cassini mission we computed a new Control Point Network (CPN) of more than 2000 points for the satellite. On this basis, we established a reference frame working model for Hyperion, useful for estimates of new shape parameters and follow-up mapping products. Consequently, we find best-fit ellipsoid parameters of 180.9 × 129.0 × 102.0 km as well as new estimates for bulk density of 565 kg/km3, which is ∼4 % more than the values previously obtained by other researchers (P.C. Thomas; R.A. Jacobson). Based on the new CPN and reference frame, global mapping products were created, which included a gridded DEM and an orthomosaic (best resolution: 50 m/pixel).
{"title":"Hyperion (S VII): Shape, mosaic and control point network","authors":"A.E. Zubarev, I.E. Nadezhdina","doi":"10.1016/j.icarus.2024.116440","DOIUrl":"10.1016/j.icarus.2024.116440","url":null,"abstract":"<div><div>Saturn's odd-shaped satellite Hyperion is unique in its chaotic rotation. Owing to limited observational data, there is currently no functional model describing the object's changing orientation in space, commonly agreed upon. Consequently, there is also no established body-fixed reference frame, critical for the creation of mapping products. Using best 166 images obtained until the end of the Cassini mission we computed a new Control Point Network (CPN) of more than 2000 points for the satellite. On this basis, we established a reference frame working model for Hyperion, useful for estimates of new shape parameters and follow-up mapping products. Consequently, we find best-fit ellipsoid parameters of 180.9 × 129.0 × 102.0 km as well as new estimates for bulk density of 565 kg/km3, which is ∼4 % more than the values previously obtained by other researchers (P.C. Thomas; R.A. Jacobson). Based on the new CPN and reference frame, global mapping products were created, which included a gridded DEM and an orthomosaic (best resolution: 50 m/pixel).</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116440"},"PeriodicalIF":2.5,"publicationDate":"2024-12-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134790","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-16DOI: 10.1016/j.icarus.2024.116439
H.I. Hargitai , P. Brož
The aim of this work was to systematically map cluster-forming Irregular Patches (IPs) on the Moon. These features, formerly termed “Irregular Mare Patches”, are enigmatic features situated on the near side of the Moon, mostly in mare regions. IPs are pristine-looking features with textures at the meter scale, suggesting they formed millions of years ago on top of several-billion-year-old mare basalts. Morphologic and spectral studies could not provide conclusive evidence of their formative processes, or their age. Theories on their formation concentrate around three conflicting models - that they are formed by compact basalts and are only a few tens of millions of years old; that they are formed by mass wasting processes capable to remove regolith to this day; or that they are composed of lava foams and their age is the same as the host terrain's, i.e. billions of years. We present a GIS-based analysis to examine which formation model is supported by their geography. Previous catalogs mapped IPs ambiguously, with one single coordinate representing one unit or a group of units, with many isolated units around them remaining unmapped. To change that, we mapped isolated IPs individually as polygons because we wanted to reveal their areas and their local-scale distribution patterns, which were not identifiable from previous mapping efforts. We named the isolated, elemental depressions Irregular Patches to differentiate them from previous works. After the mapping, we grouped these IPs into clusters. This new mapping revealed that over 2700 Irregular Patches form more than 100 clusters, often displaying characteristic patterns. Their geologic context suggests that these patterns are controlled by subsurface geologic structures and processes. This way even without penetrating radar, recognizing the clustered nature of IPs on the Moon enables us to infer details of the IP hosting regions' subsurface structures and infer subsurface processes that led to their formation.
{"title":"Clusters of irregular patches on the Moon: A new GIS-based catalog","authors":"H.I. Hargitai , P. Brož","doi":"10.1016/j.icarus.2024.116439","DOIUrl":"10.1016/j.icarus.2024.116439","url":null,"abstract":"<div><div>The aim of this work was to systematically map cluster-forming Irregular Patches (IPs) on the Moon. These features, formerly termed “Irregular Mare Patches”, are enigmatic features situated on the near side of the Moon, mostly in mare regions. IPs are pristine-looking features with textures at the meter scale, suggesting they formed millions of years ago on top of several-billion-year-old mare basalts. Morphologic and spectral studies could not provide conclusive evidence of their formative processes, or their age. Theories on their formation concentrate around three conflicting models - that they are formed by compact basalts and are only a few tens of millions of years old; that they are formed by mass wasting processes capable to remove regolith to this day; or that they are composed of lava foams and their age is the same as the host terrain's, i.e. billions of years. We present a GIS-based analysis to examine which formation model is supported by their geography. Previous catalogs mapped IPs ambiguously, with one single coordinate representing one unit or a group of units, with many isolated units around them remaining unmapped. To change that, we mapped isolated IPs individually as polygons because we wanted to reveal their areas and their local-scale distribution patterns, which were not identifiable from previous mapping efforts. We named the isolated, elemental depressions <em>Irregular Patches</em> to differentiate them from previous works. After the mapping, we grouped these IPs into clusters. This new mapping revealed that over 2700 Irregular Patches form more than 100 clusters, often displaying characteristic patterns. Their geologic context suggests that these patterns are controlled by subsurface geologic structures and processes. This way even without penetrating radar, recognizing the clustered nature of IPs on the Moon enables us to infer details of the IP hosting regions' subsurface structures and infer subsurface processes that led to their formation.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116439"},"PeriodicalIF":2.5,"publicationDate":"2024-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134553","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-16DOI: 10.1016/j.icarus.2024.116418
Zoé Perrin , Nathalie Carrasco , Thomas Gautier , Nathalie Ruscassier , Julien Maillard , Carlos Afonso , Ludovic Vettier
Titan has a climate system with similarities to Earth, including the presence of a thick atmosphere made up of several atmospheric layers. As on Earth, Titan's climate is influenced by several factors: the gaseous species making up the atmosphere, the energy deposited on the satellite, and solid organic aerosols. Indeed, numerous observations have revealed the presence of solid particles in the form of an opaque orange haze in Titan's atmosphere, influencing radiation balance and atmospheric dynamics, for example. However, the influence of these suspended solid particles seems to evolve according to the atmospheric altitude where they are located, certainly testifying to the presence of organic solids with different physico-chemical properties. At present, it is suspected that several populations/classes of atmospheric aerosols may form following different chemical pathways, and that aerosols undergo growth processes that modify their properties. In this experimental study, we present new observations on the evolution of morphological and chemical properties observed on Titan aerosol analogues, produced from a mixture of 20 % CH4 and 80 % N2 injected into a dusty RF plasma experiment. Using SEM (morphological) and FTICR-LDI-MS (chemical composition) analyses, we observe that properties evolve according to certain formation and growth mechanisms, which differentiate over time. The evolution of the neutral gaseous chemical composition analyzed in-situ by QMS in parallel shows correlations with the evolution of solid properties, testifying to the selective involvement of certain neutral products in the formation and growth mechanisms of solid aerosols. By linking the analyses of the gas phase and organic solids, we propose the calculation of an uptake coefficient between six neutral gaseous products (C2H2, HCN, C2H6, C2H3N, HC3N, C2N2) and the surface of the Titan aerosol analogues produced in this study.
{"title":"Investigating the formation and growth of Titan's atmospheric aerosols using an experimental approach","authors":"Zoé Perrin , Nathalie Carrasco , Thomas Gautier , Nathalie Ruscassier , Julien Maillard , Carlos Afonso , Ludovic Vettier","doi":"10.1016/j.icarus.2024.116418","DOIUrl":"10.1016/j.icarus.2024.116418","url":null,"abstract":"<div><div>Titan has a climate system with similarities to Earth, including the presence of a thick atmosphere made up of several atmospheric layers. As on Earth, Titan's climate is influenced by several factors: the gaseous species making up the atmosphere, the energy deposited on the satellite, and solid organic aerosols. Indeed, numerous observations have revealed the presence of solid particles in the form of an opaque orange haze in Titan's atmosphere, influencing radiation balance and atmospheric dynamics, for example. However, the influence of these suspended solid particles seems to evolve according to the atmospheric altitude where they are located, certainly testifying to the presence of organic solids with different physico-chemical properties. At present, it is suspected that several populations/classes of atmospheric aerosols may form following different chemical pathways, and that aerosols undergo growth processes that modify their properties. In this experimental study, we present new observations on the evolution of morphological and chemical properties observed on Titan aerosol analogues, produced from a mixture of 20 % CH<sub>4</sub> and 80 % N<sub>2</sub> injected into a dusty RF plasma experiment. Using SEM (morphological) and FTICR-LDI-MS (chemical composition) analyses, we observe that properties evolve according to certain formation and growth mechanisms, which differentiate over time. The evolution of the neutral gaseous chemical composition analyzed in-situ by QMS in parallel shows correlations with the evolution of solid properties, testifying to the selective involvement of certain neutral products in the formation and growth mechanisms of solid aerosols. By linking the analyses of the gas phase and organic solids, we propose the calculation of an uptake coefficient between six neutral gaseous products (C<sub>2</sub>H<sub>2</sub>, HCN, C<sub>2</sub>H<sub>6</sub>, C<sub>2</sub>H<sub>3</sub>N, HC<sub>3</sub>N, C<sub>2</sub>N<sub>2</sub>) and the surface of the Titan aerosol analogues produced in this study.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116418"},"PeriodicalIF":2.5,"publicationDate":"2024-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134791","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
<div><div>The shape of regolith particles on airless bodies, such as the Moon and asteroids, reflects the processes that occur on their surfaces. Recent studies have shown that particles on the asteroid Ryugu tend to be angular, whereas some particles on the asteroid Itokawa are rounded, with a larger portions of lunar particles also exhibiting a rounded shape. These differences are thought to result from abrasion, but experimental studies on particle abrasion have been lacking. In this study, we performed experiments simulating the abrasion caused by impact on airless bodies using minerals, rocks, and meteorites related to the Moon and asteroids. Aggregates of particles ranging in size from 1 to 2 mm (6.5 to10 g) were subjected to oscillation in a bead-milling apparatus to assess the amount of abrasion at different oscillation rates, varying from 100 to 3000 rpm for 0.33 to 720 min. The amount of abrasion increased with time and oscillation rate, following a power-law relationship. Once the oscillation rate exceeded a certain threshold, abrasion proceeded rapidly. At rates above 1000 rpm, particles floated and rubbed against each other due to the vertical oscillation of the container, leading to significant abrasion, whereas at rates below 300 rpm, the particles were constrained by Earth's gravity, resulting in minimal abrasion. This indicates that experiments conducted at ≥1000 rpm effectively simulated the abrasion that occurs on the Moon and asteroids. Scanning electron microscopy was used to observe the particles before and after the experiments, and X-ray microtomography was employed to track the shape changes of individual traceable particles and to measure the three-axial lengths of approximately160 particles. As abrasion progressed, some of the corners and edges of the particles were initially chipped, eventually leading to rounded corners, edges, and surfaces. This process corresponds to “adhesive wear” in tribology, which is caused by tangential relative motion between materials. In carbonaceous chondrite samples, particles tended to split along pre-existing cracks. The particles became smaller, their angularity decreased, and their sphericity increased, while the overall 3D shape of individual particles did not significantly change from their original form; however, the average three-axial ratio became more isotropic. These results indicate that the change in the average three-axial ratio of the Moon and Itokawa regolith particles can be explained by abrasion, as previously proposed. Based on the observed abrasion rates, we discuss the potential for abrasion to be caused by the impact-induced particle motion on the Moon and asteroids, considering models of regolith convection, excavation flow, and maximum acceleration. Although this discussion is rough and only semi-quantitative due to many assumptions, experimental errors, and uncertainties in the models, the results suggest that abrasion can occur on the Moon due to impact-induced p
{"title":"Abrasion experiments of mineral, rock, and meteorite particles: Simulating regolith particles abrasion on airless bodies","authors":"Akira Tsuchiyama , Hirotaka Yamaguchi , Motohiro Ogawa , Akiko M. Nakamura , Tatsuhiro Michikami , Kentaro Uesugi","doi":"10.1016/j.icarus.2024.116432","DOIUrl":"10.1016/j.icarus.2024.116432","url":null,"abstract":"<div><div>The shape of regolith particles on airless bodies, such as the Moon and asteroids, reflects the processes that occur on their surfaces. Recent studies have shown that particles on the asteroid Ryugu tend to be angular, whereas some particles on the asteroid Itokawa are rounded, with a larger portions of lunar particles also exhibiting a rounded shape. These differences are thought to result from abrasion, but experimental studies on particle abrasion have been lacking. In this study, we performed experiments simulating the abrasion caused by impact on airless bodies using minerals, rocks, and meteorites related to the Moon and asteroids. Aggregates of particles ranging in size from 1 to 2 mm (6.5 to10 g) were subjected to oscillation in a bead-milling apparatus to assess the amount of abrasion at different oscillation rates, varying from 100 to 3000 rpm for 0.33 to 720 min. The amount of abrasion increased with time and oscillation rate, following a power-law relationship. Once the oscillation rate exceeded a certain threshold, abrasion proceeded rapidly. At rates above 1000 rpm, particles floated and rubbed against each other due to the vertical oscillation of the container, leading to significant abrasion, whereas at rates below 300 rpm, the particles were constrained by Earth's gravity, resulting in minimal abrasion. This indicates that experiments conducted at ≥1000 rpm effectively simulated the abrasion that occurs on the Moon and asteroids. Scanning electron microscopy was used to observe the particles before and after the experiments, and X-ray microtomography was employed to track the shape changes of individual traceable particles and to measure the three-axial lengths of approximately160 particles. As abrasion progressed, some of the corners and edges of the particles were initially chipped, eventually leading to rounded corners, edges, and surfaces. This process corresponds to “adhesive wear” in tribology, which is caused by tangential relative motion between materials. In carbonaceous chondrite samples, particles tended to split along pre-existing cracks. The particles became smaller, their angularity decreased, and their sphericity increased, while the overall 3D shape of individual particles did not significantly change from their original form; however, the average three-axial ratio became more isotropic. These results indicate that the change in the average three-axial ratio of the Moon and Itokawa regolith particles can be explained by abrasion, as previously proposed. Based on the observed abrasion rates, we discuss the potential for abrasion to be caused by the impact-induced particle motion on the Moon and asteroids, considering models of regolith convection, excavation flow, and maximum acceleration. Although this discussion is rough and only semi-quantitative due to many assumptions, experimental errors, and uncertainties in the models, the results suggest that abrasion can occur on the Moon due to impact-induced p","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116432"},"PeriodicalIF":2.5,"publicationDate":"2024-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143135205","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-12DOI: 10.1016/j.icarus.2024.116431
Jordyn A. Robare , Everett L. Shock
The search for life in our solar system often involves efforts to detect organic molecules, which have been found on many extraterrestrial bodies, including planets, moons, meteorites, comets, and asteroids. These chemical signatures are not typically thought of as biosignatures because we know that organic synthesis can occur through abiotic processes. Therefore, development of methods for distinguishing biotic and abiotic biosignatures would enable interpretation of data collected from habitability and life-detection missions. Life on Earth harnesses energy-releasing reactions to power biosynthesis reactions, which often require energy. Using thermodynamic data, we can quantify the energy required for organic synthesis. If an organic molecule is detected in an abundance that is thermodynamically unstable, then it is possible that life coupled its synthesis to other energy-releasing reactions. On the other hand, if an organic molecule is detected in an abundance that is thermodynamically stable, then abiotic synthesis was plausible. This sorting framework can be applied to the search for life wherever we have geochemical data. One such example is Saturn's moon Enceladus. Small compounds involving the elements that comprise the majority of biomass were detected by the Cassini spacecraft in the plume gas erupting from the subsurface ocean. Using Enceladus as an example, we demonstrate the utility of thermodynamic calculations for distinguishing biosignatures and show that organic synthesis is often favorable using the carbon sources available on Enceladus. While these results may lead us to conclude that hypothetical organic signatures on Enceladus are abiotic, this framework can be applied to other environments in the search for genuine biosignatures.
{"title":"Distinguishing potential organic biosignatures on ocean worlds from abiotic geochemical products using thermodynamic calculations","authors":"Jordyn A. Robare , Everett L. Shock","doi":"10.1016/j.icarus.2024.116431","DOIUrl":"10.1016/j.icarus.2024.116431","url":null,"abstract":"<div><div>The search for life in our solar system often involves efforts to detect organic molecules, which have been found on many extraterrestrial bodies, including planets, moons, meteorites, comets, and asteroids. These chemical signatures are not typically thought of as biosignatures because we know that organic synthesis can occur through abiotic processes. Therefore, development of methods for distinguishing biotic and abiotic biosignatures would enable interpretation of data collected from habitability and life-detection missions. Life on Earth harnesses energy-releasing reactions to power biosynthesis reactions, which often require energy. Using thermodynamic data, we can quantify the energy required for organic synthesis. If an organic molecule is detected in an abundance that is thermodynamically unstable, then it is possible that life coupled its synthesis to other energy-releasing reactions. On the other hand, if an organic molecule is detected in an abundance that is thermodynamically stable, then abiotic synthesis was plausible. This sorting framework can be applied to the search for life wherever we have geochemical data. One such example is Saturn's moon Enceladus. Small compounds involving the elements that comprise the majority of biomass were detected by the Cassini spacecraft in the plume gas erupting from the subsurface ocean. Using Enceladus as an example, we demonstrate the utility of thermodynamic calculations for distinguishing biosignatures and show that organic synthesis is often favorable using the carbon sources available on Enceladus. While these results may lead us to conclude that hypothetical organic signatures on Enceladus are abiotic, this framework can be applied to other environments in the search for genuine biosignatures.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116431"},"PeriodicalIF":2.5,"publicationDate":"2024-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134792","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-10DOI: 10.1016/j.icarus.2024.116421
Mireia Leon-Dasi , Sebastien Besse , Lauren M. Jozwiak , Erica R. Jawin , Alain Doressoundiram
Explosive volcanic activity on Mercury extended after the end of the widespread effusive volcanism era. While prior research has recognized a prolonged period of explosive volcanic activity, the specific eruption timing for individual pyroclastic deposits remains unknown. In this study, we explore the evolution of explosive volcanism by examining the relationship between the morphological degradation of the vents and spectral changes in the associated deposits. We find a diverse range of spectral properties in pyroclastic deposits, which are typically characterized by increased brightness, a red spectral slope, and a higher curvature compared to the average surface. Rather than presenting a unique spectral signature, these deposits exhibit spectral parameters that span the range of most units on Mercury. We observe a trend between the deposit spectra and the vent degradation characterized by a rapid initial darkening and flattening over time followed by stabilization. The oldest deposits reach a steady state with no further spectral changes. To explain these temporal variations in spectral properties, we propose three potential processes: space weathering, mixing with the background and changes in pyroclast size over time. We examine the implications of space weathering on spectral properties and discuss the eruption timeline for each scenario. The saturation of spectral changes induced by space weathering acts over a period of 1 Gyr. We suggest that a large portion of the pyroclastic deposits identified to date, which have a marked spectral contrast with the surrounding terrain, have been emplaced by recent explosive volcanic eruptions.
{"title":"Timing of explosive volcanism on Mercury: A morphological and spectral analysis","authors":"Mireia Leon-Dasi , Sebastien Besse , Lauren M. Jozwiak , Erica R. Jawin , Alain Doressoundiram","doi":"10.1016/j.icarus.2024.116421","DOIUrl":"10.1016/j.icarus.2024.116421","url":null,"abstract":"<div><div>Explosive volcanic activity on Mercury extended after the end of the widespread effusive volcanism era. While prior research has recognized a prolonged period of explosive volcanic activity, the specific eruption timing for individual pyroclastic deposits remains unknown. In this study, we explore the evolution of explosive volcanism by examining the relationship between the morphological degradation of the vents and spectral changes in the associated deposits. We find a diverse range of spectral properties in pyroclastic deposits, which are typically characterized by increased brightness, a red spectral slope, and a higher curvature compared to the average surface. Rather than presenting a unique spectral signature, these deposits exhibit spectral parameters that span the range of most units on Mercury. We observe a trend between the deposit spectra and the vent degradation characterized by a rapid initial darkening and flattening over time followed by stabilization. The oldest deposits reach a steady state with no further spectral changes. To explain these temporal variations in spectral properties, we propose three potential processes: space weathering, mixing with the background and changes in pyroclast size over time. We examine the implications of space weathering on spectral properties and discuss the eruption timeline for each scenario. The saturation of spectral changes induced by space weathering acts over a period of 1 Gyr. We suggest that a large portion of the pyroclastic deposits identified to date, which have a marked spectral contrast with the surrounding terrain, have been emplaced by recent explosive volcanic eruptions.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116421"},"PeriodicalIF":2.5,"publicationDate":"2024-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134725","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-10DOI: 10.1016/j.icarus.2024.116436
Benjamin D. Boatwright, James W. Head
The characterization of crater degradation on Mars has been closely tied to the development of landform evolution models whose goals have been to better understand the influence of climate-driven erosive processes. Three types of landform evolution are generally identified: aggradation, advection, and diffusion. Many different processes have been invoked to explain the diffusive degradation of impact craters on Mars, some of which are climate-dependent. The prevalence of topographic diffusion from subsequent small impacts on the Moon suggests that similar processes may have been operating on the surface of Mars throughout its history. We find that the effectiveness of impact-induced diffusive degradation on Mars is highly dependent upon both atmospheric pressure and the size scaling of impact craters. Thus, it is critical that further quantitative observations be made of diffusively degraded craters on Mars in order to determine whether impact-induced diffusion has had a measurable effect on the evolution of the martian landscape.
{"title":"The importance of impacts in Mars crater degradation: Predictions for atmospheric filtering of small impactors","authors":"Benjamin D. Boatwright, James W. Head","doi":"10.1016/j.icarus.2024.116436","DOIUrl":"10.1016/j.icarus.2024.116436","url":null,"abstract":"<div><div>The characterization of crater degradation on Mars has been closely tied to the development of landform evolution models whose goals have been to better understand the influence of climate-driven erosive processes. Three types of landform evolution are generally identified: aggradation, advection, and diffusion. Many different processes have been invoked to explain the diffusive degradation of impact craters on Mars, some of which are climate-dependent. The prevalence of topographic diffusion from subsequent small impacts on the Moon suggests that similar processes may have been operating on the surface of Mars throughout its history. We find that the effectiveness of impact-induced diffusive degradation on Mars is highly dependent upon both atmospheric pressure and the size scaling of impact craters. Thus, it is critical that further quantitative observations be made of diffusively degraded craters on Mars in order to determine whether impact-induced diffusion has had a measurable effect on the evolution of the martian landscape.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116436"},"PeriodicalIF":2.5,"publicationDate":"2024-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134540","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-10DOI: 10.1016/j.icarus.2024.116428
Leandro Esteves , André Izidoro , Othon C. Winter
The origins of Uranus and Neptune are not fully understood. Their inclined rotation axes – obliquities – suggest that they experienced giant impacts during their formation histories. Simulations modeling their accretion from giant impacts among 5 Earth masses planetary embryos – with roughly unity impactors’ mass ratios – have been able to broadly match their current masses, final mass ratio, and obliquity. However, due to angular momentum conservation, planets produced in these impacts tend to rotate too fast, compared to Uranus and Neptune. One potential solution for this problem consists of invoking instead collisions of objects with large mass ratios (e.g. a proto-Uranus with 13 M and an embryo of 1 M). Smooth-particle hydrodynamics simulations show that in this scenario final planets tend to have rotation periods more consistent with those of Uranus and Neptune. Here we performed a large suite of N-body numerical simulations modeling the formation of Uranus and Neptune to compare these different dynamical views. Our simulations start with a population of protoplanets and account for the effects of type-I migration, inclination and eccentricity tidal damping. Our results show that although scenarios allowing for large impactors’ mass ratio favor slower rotating planets, the probability of occurring collisions in these specific simulations is significantly low. This is because gas tidal damping is relatively less efficient for low-mass embryos (1 M) and, consequently, such objects are mostly scattered by more massive objects (13 M) instead of colliding with them. Altogether, our results show that the probability of broadly matching the masses, mass ratio, and rotation periods of Uranus and Neptune in these two competing formation scenarios is broadly similar, within a factor of 2, with overall probabilities of the order of 0.1%–1%.
{"title":"Accretion of Uranus and Neptune: Confronting different giant impact scenarios","authors":"Leandro Esteves , André Izidoro , Othon C. Winter","doi":"10.1016/j.icarus.2024.116428","DOIUrl":"10.1016/j.icarus.2024.116428","url":null,"abstract":"<div><div>The origins of Uranus and Neptune are not fully understood. Their inclined rotation axes – obliquities – suggest that they experienced giant impacts during their formation histories. Simulations modeling their accretion from giant impacts among <span><math><mo>∼</mo></math></span>5 Earth masses planetary embryos – with roughly unity impactors’ mass ratios – have been able to broadly match their current masses, final mass ratio, and obliquity. However, due to angular momentum conservation, planets produced in these impacts tend to rotate too fast, compared to Uranus and Neptune. One potential solution for this problem consists of invoking instead collisions of objects with large mass ratios (e.g. a proto-Uranus with 13 M<span><math><msub><mrow></mrow><mrow><mo>⊕</mo></mrow></msub></math></span> and an embryo of 1 M<span><math><msub><mrow></mrow><mrow><mo>⊕</mo></mrow></msub></math></span>). Smooth-particle hydrodynamics simulations show that in this scenario final planets tend to have rotation periods more consistent with those of Uranus and Neptune. Here we performed a large suite of N-body numerical simulations modeling the formation of Uranus and Neptune to compare these different dynamical views. Our simulations start with a population of protoplanets and account for the effects of type-I migration, inclination and eccentricity tidal damping. Our results show that although scenarios allowing for large impactors’ mass ratio favor slower rotating planets, the probability of occurring collisions in these specific simulations is significantly low. This is because gas tidal damping is relatively less efficient for low-mass embryos (<span><math><mo>≲</mo></math></span>1 M<span><math><msub><mrow></mrow><mrow><mo>⊕</mo></mrow></msub></math></span>) and, consequently, such objects are mostly scattered by more massive objects (<span><math><mo>∼</mo></math></span>13 M<span><math><msub><mrow></mrow><mrow><mo>⊕</mo></mrow></msub></math></span>) instead of colliding with them. Altogether, our results show that the probability of broadly matching the masses, mass ratio, and rotation periods of Uranus and Neptune in these two competing formation scenarios is broadly similar, within a factor of <span><math><mo>∼</mo></math></span>2, with overall probabilities of the order of <span><math><mo>∼</mo></math></span>0.1%–1%.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116428"},"PeriodicalIF":2.5,"publicationDate":"2024-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143135206","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-09DOI: 10.1016/j.icarus.2024.116429
B.G. Rider-Stokes , S.L. Jackson , T.H. Burbine , L.F. White , R.C. Greenwood , E.M. MacLennan , M. Anand , A. Yamaguchi , M.M. Grady
It is hypothesized that the Solar System was once populated by Moon to Mars-sized planetary embryos, however, resulting debris from their disruptions is not easily discernible in the modern-day Solar System. Angrites are among the oldest differentiated materials in our Solar System, recording prolonged magmatism, and their parent body is expected to have been Moon to Mars-sized. Even so, no parent body in the modern-day Solar System has been identified. Our UV–Vis-NIR spectra of ten angrites, compared with 712 asteroids, reveal multiple candidates with spectral similarities through curve matching and band-structure analysis. Asteroid (246) Asporina provides the best analog for the angrite meteorites, potentially representing a fragment of a long-lost Moon to Mars-sized body that once resided in the inner Solar System, which was subsequently incorporated into the growing terrestrial planets.
{"title":"Remnants of a lost Planetesimal: Searching for the Angrite parent body","authors":"B.G. Rider-Stokes , S.L. Jackson , T.H. Burbine , L.F. White , R.C. Greenwood , E.M. MacLennan , M. Anand , A. Yamaguchi , M.M. Grady","doi":"10.1016/j.icarus.2024.116429","DOIUrl":"10.1016/j.icarus.2024.116429","url":null,"abstract":"<div><div>It is hypothesized that the Solar System was once populated by Moon to Mars-sized planetary embryos, however, resulting debris from their disruptions is not easily discernible in the modern-day Solar System. Angrites are among the oldest differentiated materials in our Solar System, recording prolonged magmatism, and their parent body is expected to have been Moon to Mars-sized. Even so, no parent body in the modern-day Solar System has been identified. Our UV–Vis-NIR spectra of ten angrites, compared with 712 asteroids, reveal multiple candidates with spectral similarities through curve matching and band-structure analysis. Asteroid (246) Asporina provides the best analog for the angrite meteorites, potentially representing a fragment of a long-lost Moon to Mars-sized body that once resided in the inner Solar System, which was subsequently incorporated into the growing terrestrial planets.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116429"},"PeriodicalIF":2.5,"publicationDate":"2024-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134799","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
<div><div>Jupiter’s Equatorial Zone (EZ) is characterized by atmospheric dynamics influenced by strong zonal jets. Initially, we perform a linear stability analysis of two-layer geostrophic flows to explore the growth and evolution of instabilities associated with equatorial jets. Stability diagrams reveal that the most unstable baroclinic modes shift to lower wavenumbers with increasing zonal velocities, indicating sensitivity to the strength of the zonal wind. We show notable differences in phase velocities between barotropic and baroclinic jets. Phase portraits of the dynamic structures of various wave types, including barotropic and baroclinic Kelvin waves, Yanai waves, Rossby waves, and inertia-gravity waves, are illustrated in this analysis. Subsequently, we employ a two-layer moist convective Rotating Shallow Water (2mcRSW) model to investigate the nonlinear interactions between ammonia-driven convective processes in the shallow upper atmosphere and large-scale atmospheric features in Jupiter’s EZ. We analyze the evolution of nonlinear instabilities in moist-convective flows by perturbing a background zonal velocity field with the most unstable mode. Findings include the amplification of cyclonic and anticyclonic vortices driven by moist convection at the boundaries of the zonal jets and the suppression of convective vortices in equatorial bright zones. This study underscores the role of moist convection in generating upper atmosphere cloud clusters and lightning patterns, as well as the chevron-shaped pattern observed on the poleward side of the zonal jets. Finally, we propose a novel mechanism for the formation of Y-shaped structures on Jupiter, driven by equatorial modons coupled with convectively baroclinic Kelvin waves (CCBCKWs). This mechanism suggests that Y-shaped structures result from large-scale localized heating in a diabatic environment, which, upon reaching a critical threshold of negative pressure or positive buoyancy anomaly, generates a <em>hybrid structure</em>. This <em>hybrid structure</em> consists of a <em>quasi equatorial modon</em>, a coherent dipolar structure, coupled with a CCBCKW that propagates eastward in a self-sustaining and self-propelled manner. Initially, the hybrid moves steadily eastward; however, the larger phase speed of the CCBCKW eventually leads to its detachment from the <em>quasi equatorial modon</em>. The lifetime of this coupled structure varies from interseasonal to seasonal timescales. Moist convection is a necessary condition for triggering the eastward-propagating structure.</div><div><strong>Key Points</strong>:</div><div>(1) <strong>Stability Analysis Insights:</strong> The study reveals the most unstable modes, dispersion relation, and their phase portraits in Jupiter’s Equatorial Zone, with distinct patterns observed in barotropic and baroclinic stability analyses.</div><div>(2) <strong>Moist Convection Effects:</strong> Nonlinear simulations show that moist convection amplifies cycloni
{"title":"Dynamics of Jupiter’s equatorial zone: Instability analysis and a mechanism for Y-shaped structures","authors":"Masoud Rostami , Bijan Fallah , Farahnaz Fazel-Rastgar","doi":"10.1016/j.icarus.2024.116414","DOIUrl":"10.1016/j.icarus.2024.116414","url":null,"abstract":"<div><div>Jupiter’s Equatorial Zone (EZ) is characterized by atmospheric dynamics influenced by strong zonal jets. Initially, we perform a linear stability analysis of two-layer geostrophic flows to explore the growth and evolution of instabilities associated with equatorial jets. Stability diagrams reveal that the most unstable baroclinic modes shift to lower wavenumbers with increasing zonal velocities, indicating sensitivity to the strength of the zonal wind. We show notable differences in phase velocities between barotropic and baroclinic jets. Phase portraits of the dynamic structures of various wave types, including barotropic and baroclinic Kelvin waves, Yanai waves, Rossby waves, and inertia-gravity waves, are illustrated in this analysis. Subsequently, we employ a two-layer moist convective Rotating Shallow Water (2mcRSW) model to investigate the nonlinear interactions between ammonia-driven convective processes in the shallow upper atmosphere and large-scale atmospheric features in Jupiter’s EZ. We analyze the evolution of nonlinear instabilities in moist-convective flows by perturbing a background zonal velocity field with the most unstable mode. Findings include the amplification of cyclonic and anticyclonic vortices driven by moist convection at the boundaries of the zonal jets and the suppression of convective vortices in equatorial bright zones. This study underscores the role of moist convection in generating upper atmosphere cloud clusters and lightning patterns, as well as the chevron-shaped pattern observed on the poleward side of the zonal jets. Finally, we propose a novel mechanism for the formation of Y-shaped structures on Jupiter, driven by equatorial modons coupled with convectively baroclinic Kelvin waves (CCBCKWs). This mechanism suggests that Y-shaped structures result from large-scale localized heating in a diabatic environment, which, upon reaching a critical threshold of negative pressure or positive buoyancy anomaly, generates a <em>hybrid structure</em>. This <em>hybrid structure</em> consists of a <em>quasi equatorial modon</em>, a coherent dipolar structure, coupled with a CCBCKW that propagates eastward in a self-sustaining and self-propelled manner. Initially, the hybrid moves steadily eastward; however, the larger phase speed of the CCBCKW eventually leads to its detachment from the <em>quasi equatorial modon</em>. The lifetime of this coupled structure varies from interseasonal to seasonal timescales. Moist convection is a necessary condition for triggering the eastward-propagating structure.</div><div><strong>Key Points</strong>:</div><div>(1) <strong>Stability Analysis Insights:</strong> The study reveals the most unstable modes, dispersion relation, and their phase portraits in Jupiter’s Equatorial Zone, with distinct patterns observed in barotropic and baroclinic stability analyses.</div><div>(2) <strong>Moist Convection Effects:</strong> Nonlinear simulations show that moist convection amplifies cycloni","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"429 ","pages":"Article 116414"},"PeriodicalIF":2.5,"publicationDate":"2024-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143134541","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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