Pub Date : 2024-11-20DOI: 10.1016/j.icarus.2024.116381
Q. Williams
The accuracy of the pressure/temperature/composition parameterization of Buono and Walker (2011) to describe the liquidus of iron and the Fe-FeS system is examined. In the pressure range critical for asteroidal core crystallization (0- ∼2 GPa), the model predicts a shape for the iron melting curve (initially negatively sloped, and turning over near 0.7 GPa) that is inconsistent with previous experimental observations, thermodynamic constraints, and millennia of empirical metallurgical observations. Dodds et al. (2025) recently used this model to derive notable conclusions about the behavior of the solidifying cores of asteroids: the robustness of their conclusions is assessed. Two basic caveat emptor guidelines for employing parameterizations of phase equilibria data are suggested: (1) ensure that the model's fit is consistent with simple thermodynamic expectations; and (2) verify that the data used to formulate the model provide adequate coverage in the region of interest.
{"title":"A note on the direction of core solidification in asteroids, the iron melting curve, and phase equilibria parameterizations","authors":"Q. Williams","doi":"10.1016/j.icarus.2024.116381","DOIUrl":"10.1016/j.icarus.2024.116381","url":null,"abstract":"<div><div>The accuracy of the pressure/temperature/composition parameterization of Buono and Walker (2011) to describe the liquidus of iron and the Fe-FeS system is examined. In the pressure range critical for asteroidal core crystallization (0- ∼2 GPa), the model predicts a shape for the iron melting curve (initially negatively sloped, and turning over near 0.7 GPa) that is inconsistent with previous experimental observations, thermodynamic constraints, and millennia of empirical metallurgical observations. Dodds et al. (2025) recently used this model to derive notable conclusions about the behavior of the solidifying cores of asteroids: the robustness of their conclusions is assessed. Two basic caveat emptor guidelines for employing parameterizations of phase equilibria data are suggested: (1) ensure that the model's fit is consistent with simple thermodynamic expectations; and (2) verify that the data used to formulate the model provide adequate coverage in the region of interest.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"427 ","pages":"Article 116381"},"PeriodicalIF":2.5,"publicationDate":"2024-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142706041","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}
The spectroscopic technique of laser-induced breakdown spectroscopy (LIBS) is a powerful method to perform rapid chemical analysis of geologic samples with short measurement times and no need for sample preparation. After the ChemCam instrument aboard NASA’s MSL rover proved its suitability for space missions that explore planetary surfaces in 2012, the interest in LIBS instruments as payloads has grown and several subsequent missions have successfully used this technique since. The characteristics of a LIBS plasma depend on experimental and environmental parameters as well as on sample properties, including atmospheric conditions, laser irradiance and sample lithology. Consequently, LIBS instruments need to be designed and optimized specifically for each use case to maximize their science output. To aid in the development of new LIBS instruments for space exploration, we investigate the influence of atmospheric conditions, laser irradiance and sample lithology on the lifetime, size and emission of laser-induced plasmas. In our measurements, we use a plasma imaging setup with high temporal resolution of down to 2 ns to investigate the evolution of the plasma from its ignition to its decay. We present a comparable data set recorded at terrestrial, Martian and airless atmospheric conditions, covering irradiances between 0.79 GW/mmˆ2 and 1.43 GW/mmˆ2 and samples with diverse properties, namely basalt and soapstone, as well as the lunar regolith simulants LHS-1 and LMS-1. Our measurements show the strong influence of atmospheric conditions on the plasma size and emission, while the lithologies and laser irradiances covered in this work play a minor role. This shows that instruments designed to work at certain atmospheric conditions can be used for a range of laser parameters and sample properties. Furthermore, we demonstrate that the decay of the plasma emission and the expansion of the plasma plume parallel to the sample surface can be described well by a power law and a drag model, respectively.
{"title":"Lifetime, size and emission of laser-induced plasmas for in-situ laser-induced breakdown spectroscopy on Earth, Mars and Moon","authors":"Fabian Seel , Susanne Schröder , Elise Clavé , Enrico Dietz , Peder Bagge Hansen , Kristin Rammelkamp , Heinz-Wilhelm Hübers","doi":"10.1016/j.icarus.2024.116376","DOIUrl":"10.1016/j.icarus.2024.116376","url":null,"abstract":"<div><div>The spectroscopic technique of laser-induced breakdown spectroscopy (LIBS) is a powerful method to perform rapid chemical analysis of geologic samples with short measurement times and no need for sample preparation. After the ChemCam instrument aboard NASA’s MSL rover proved its suitability for space missions that explore planetary surfaces in 2012, the interest in LIBS instruments as payloads has grown and several subsequent missions have successfully used this technique since. The characteristics of a LIBS plasma depend on experimental and environmental parameters as well as on sample properties, including atmospheric conditions, laser irradiance and sample lithology. Consequently, LIBS instruments need to be designed and optimized specifically for each use case to maximize their science output. To aid in the development of new LIBS instruments for space exploration, we investigate the influence of atmospheric conditions, laser irradiance and sample lithology on the lifetime, size and emission of laser-induced plasmas. In our measurements, we use a plasma imaging setup with high temporal resolution of down to 2<!--> <!-->ns to investigate the evolution of the plasma from its ignition to its decay. We present a comparable data set recorded at terrestrial, Martian and airless atmospheric conditions, covering irradiances between 0.79<!--> <!-->GW/mmˆ2 and 1.43<!--> <!-->GW/mmˆ2 and samples with diverse properties, namely basalt and soapstone, as well as the lunar regolith simulants LHS-1 and LMS-1. Our measurements show the strong influence of atmospheric conditions on the plasma size and emission, while the lithologies and laser irradiances covered in this work play a minor role. This shows that instruments designed to work at certain atmospheric conditions can be used for a range of laser parameters and sample properties. Furthermore, we demonstrate that the decay of the plasma emission and the expansion of the plasma plume parallel to the sample surface can be described well by a power law and a drag model, respectively.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"427 ","pages":"Article 116376"},"PeriodicalIF":2.5,"publicationDate":"2024-11-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142706042","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 : 2024-11-19DOI: 10.1016/j.icarus.2024.116370
Sin-iti Sirono
An icy grain in a protoplanetary nebula mainly consists of amorphous HO ice and can grow through the migration of HO molecules (sintering). The growth rate through sintering strongly depends on the diffusion constant of HO molecules. I estimated the size of amorphous ice grains as a function of the sintering duration based on the diffusion constant of amorphous ice determined by the molecular dynamics simulation. It has been found that the growth proceeds in a wide disk region (AU), and grain can grow to cm around the snowline. The growth of the icy grains can affect the evolution of the icy dust aggregates in a protoplanetary disk.
{"title":"Growth of amorphous ice grains by sintering in a protoplanetary disk","authors":"Sin-iti Sirono","doi":"10.1016/j.icarus.2024.116370","DOIUrl":"10.1016/j.icarus.2024.116370","url":null,"abstract":"<div><div>An icy grain in a protoplanetary nebula mainly consists of amorphous H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O ice and can grow through the migration of H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O molecules (sintering). The growth rate through sintering strongly depends on the diffusion constant of H<span><math><msub><mrow></mrow><mrow><mn>2</mn></mrow></msub></math></span>O molecules. I estimated the size of amorphous ice grains as a function of the sintering duration based on the diffusion constant of amorphous ice determined by the molecular dynamics simulation. It has been found that the growth proceeds in a wide disk region (<span><math><mrow><mo>∼</mo><mn>20</mn><mspace></mspace></mrow></math></span>AU), and grain can grow to <span><math><mrow><mo>∼</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mo>−</mo><mn>3</mn></mrow></msup><mspace></mspace></mrow></math></span>cm around the snowline. The growth of the icy grains can affect the evolution of the icy dust aggregates in a protoplanetary disk.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"427 ","pages":"Article 116370"},"PeriodicalIF":2.5,"publicationDate":"2024-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142706044","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 : 2024-11-19DOI: 10.1016/j.icarus.2024.116374
Sana Ahmed , Kinsuk Acharyya
Comets are a rich reservoir of complex organic molecules. Ground and space-based observatories have recently greatly enhanced the cometary molecular inventory. Although these molecules’ origin is believed to be the cometary nucleus, they can be partially synthesized in the coma. We studied organic molecules’ nucleus versus coma origins for various initial conditions, using a multifluid chemical-hydrodynamical model and an updated chemical network. For the study, we considered four comets [C/1996 B2 (Hyakutake), C/2012 F6 (Lemmon), C/2013 R1 (Lovejoy), and C/2014 Q2 (Lovejoy)] due to their relatively high activity and observation of large number of organic species. We emphasized on the C-H-O and N-bearing species, including the simplest amino acid, glycine. We discuss the formation pathways of the organics and the conditions for their formation in the coma and find that the abundance varies from one comet to another due to differences in the initial conditions, relative abundances of the reactants and temperature. We compare the organic abundances when they are present as parent volatiles to their formation solely due to gas-phase chemistry. Their abundance purely due to the coma chemistry is moderately to significantly lower compared to that when they are parent volatiles. However, we find that the production rates of some of the coma-synthesized organic molecules can reach peak values of molecules s−1, which is in the realm of detection by in situ/space-based observations, and can therefore be important considering future missions to comets. We also compare our modeled abundances with those observed in 67P/C-G by Rosetta, which detected several organics at a large heliocentric distance and low production rate.
{"title":"The extent of formation of organic molecules in the comae of comets showing relatively high activity","authors":"Sana Ahmed , Kinsuk Acharyya","doi":"10.1016/j.icarus.2024.116374","DOIUrl":"10.1016/j.icarus.2024.116374","url":null,"abstract":"<div><div>Comets are a rich reservoir of complex organic molecules. Ground and space-based observatories have recently greatly enhanced the cometary molecular inventory. Although these molecules’ origin is believed to be the cometary nucleus, they can be partially synthesized in the coma. We studied organic molecules’ nucleus versus coma origins for various initial conditions, using a multifluid chemical-hydrodynamical model and an updated chemical network. For the study, we considered four comets [C/1996 B2 (Hyakutake), C/2012 F6 (Lemmon), C/2013 R1 (Lovejoy), and C/2014 Q2 (Lovejoy)] due to their relatively high activity and observation of large number of organic species. We emphasized on the C-H-O and N-bearing species, including the simplest amino acid, glycine. We discuss the formation pathways of the organics and the conditions for their formation in the coma and find that the abundance varies from one comet to another due to differences in the initial conditions, relative abundances of the reactants and temperature. We compare the organic abundances when they are present as parent volatiles to their formation solely due to gas-phase chemistry. Their abundance purely due to the coma chemistry is moderately to significantly lower compared to that when they are parent volatiles. However, we find that the production rates of some of the coma-synthesized organic molecules can reach peak values of <span><math><mrow><mo>∼</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>22</mn></mrow></msup><mo>−</mo><mn>1</mn><msup><mrow><mn>0</mn></mrow><mrow><mn>26</mn></mrow></msup></mrow></math></span> molecules s<sup>−1</sup>, which is in the realm of detection by in situ/space-based observations, and can therefore be important considering future missions to comets. We also compare our modeled abundances with those observed in 67P/C-G by <em>Rosetta</em>, which detected several organics at a large heliocentric distance and low production rate.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"427 ","pages":"Article 116374"},"PeriodicalIF":2.5,"publicationDate":"2024-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142706114","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 : 2024-11-19DOI: 10.1016/j.icarus.2024.116372
Paul Lagouanelle, Alice Le Gall
Among the lines of evidence for a buried ocean on Titan is the possible detection of Schumann-like Resonances (SR), in 2005, by the Permittivity, Wave and Altimetry (PWA) analyzer on board the ESA Huygens probe. SR are Extremely Low Frequency electromagnetic waves resonating between two electrically conductive layers. On Titan, it has been proposed that they propagate between the moon’s ionosphere and a salty subsurface water ocean. Their characterization by electric field sensors can provide constraints on Titan’s cavity characteristics and in particular on the depth of Titan’s ocean which is key to better assess Titan’s habitability. For this work we have developed a numerical model of Titan’s electromagnetic cavity as well as a surrogate model (i.e., an approximate mathematical model) able to accurately approximate the behavior of the cavity. This surrogate model can be used to conduct simulations and sensitivity analyses at a low computational cost. It is used both to re-assess PWA/Huygens measurements and to predict the future performance of the EFIELD experiment on board the NASA Dragonfly mission. We demonstrate that the PWA/Huygens measurements, in particular due to their low spectral resolution, do not bring any meaningful constraint on Titan’s ocean depth. On the other hand, the finer resolution of the EFIELD experiment and its ability to capture several harmonics of SR should provide more robust constraints on Titan’s internal structure, especially if the electrical properties of the ice crust and the atmosphere can be better constrained.
{"title":"Schumann Resonances as a tool to constrain the depth of Titan’s buried water ocean: Re-assessment of Huygens observations and preparation of the EFIELD/Dragonfly experiment","authors":"Paul Lagouanelle, Alice Le Gall","doi":"10.1016/j.icarus.2024.116372","DOIUrl":"10.1016/j.icarus.2024.116372","url":null,"abstract":"<div><div>Among the lines of evidence for a buried ocean on Titan is the possible detection of Schumann-like Resonances (SR), in 2005, by the Permittivity, Wave and Altimetry (PWA) analyzer on board the ESA Huygens probe. SR are Extremely Low Frequency electromagnetic waves resonating between two electrically conductive layers. On Titan, it has been proposed that they propagate between the moon’s ionosphere and a salty subsurface water ocean. Their characterization by electric field sensors can provide constraints on Titan’s cavity characteristics and in particular on the depth of Titan’s ocean which is key to better assess Titan’s habitability. For this work we have developed a numerical model of Titan’s electromagnetic cavity as well as a surrogate model (i.e., an approximate mathematical model) able to accurately approximate the behavior of the cavity. This surrogate model can be used to conduct simulations and sensitivity analyses at a low computational cost. It is used both to re-assess PWA/Huygens measurements and to predict the future performance of the EFIELD experiment on board the NASA Dragonfly mission. We demonstrate that the PWA/Huygens measurements, in particular due to their low spectral resolution, do not bring any meaningful constraint on Titan’s ocean depth. On the other hand, the finer resolution of the EFIELD experiment and its ability to capture several harmonics of SR should provide more robust constraints on Titan’s internal structure, especially if the electrical properties of the ice crust and the atmosphere can be better constrained.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"428 ","pages":"Article 116372"},"PeriodicalIF":2.5,"publicationDate":"2024-11-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142745838","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 : 2024-11-17DOI: 10.1016/j.icarus.2024.116377
Joseph S. Levy , Thomas F. Subak , Ian Armstrong , Izzy King , Lingfeng Kuang , Lily Kuentz , James H. Gearon , Sophie Naylor , M.C. Rapoza , Haobo Wang
The interlocking plateaus of martian chaotic terrain have long been inferred to relate to Hesperian outflow-channel megafloods. Numerous hypotheses have been invoked to explain the formation of the hundreds-of-kilometer-scale depressions that chaoses are found in, and the mechanisms by which the fractures formed. Hypotheses range from mechanisms involving water, e.g., ice melt, overturn of sediment-covered paleolakes, or submarine landslides, to purely magmatic processes, such as caldera formation, to exotic endmembers including clathrate decomposition. These interpretations of martian chaos are largely based on photogeological mapping of individual chaoses, and have mostly neglected analysis of the chaos fracture network and its relationships with the chaos basin. Here, we show, based on analysis of 35,964 fracture blocks across 18 different chaoses and 6 terrestrial analogs, and supported by novel volumetric measurements of chaos terrain deposits and intervening void spaces, that the geometry of martian chaoses is best explained by depressurization and compaction of an underlying confined aquifer. Block size distributions are incompatible with magma chamber collapse analog experiments. We show that sedimentary fill in chaos basins is inhomogeneously distributed, with layers thickening towards the chaos center, as in terrestrial sedimentary basins. The relationship between fracture block thickness and area is explained by the same power law that describes fracture spacing and layer thickness in weak terrestrial sandstones. The presence of some chaoses with blocks that are higher than surrounding plains implies repressurization of some sub-chaos aquifers. Hesperian-aged water or ice may remain within ∼1–3 km of the surface beneath these landforms.
{"title":"Martian Chaos terrain fracture geometry indicates drainage and compaction of laterally heterogeneous confined aquifers","authors":"Joseph S. Levy , Thomas F. Subak , Ian Armstrong , Izzy King , Lingfeng Kuang , Lily Kuentz , James H. Gearon , Sophie Naylor , M.C. Rapoza , Haobo Wang","doi":"10.1016/j.icarus.2024.116377","DOIUrl":"10.1016/j.icarus.2024.116377","url":null,"abstract":"<div><div>The interlocking plateaus of martian chaotic terrain have long been inferred to relate to Hesperian outflow-channel megafloods. Numerous hypotheses have been invoked to explain the formation of the hundreds-of-kilometer-scale depressions that chaoses are found in, and the mechanisms by which the fractures formed. Hypotheses range from mechanisms involving water, e.g., ice melt, overturn of sediment-covered paleolakes, or submarine landslides, to purely magmatic processes, such as caldera formation, to exotic endmembers including clathrate decomposition. These interpretations of martian chaos are largely based on photogeological mapping of individual chaoses, and have mostly neglected analysis of the chaos fracture network and its relationships with the chaos basin. Here, we show, based on analysis of 35,964 fracture blocks across 18 different chaoses and 6 terrestrial analogs, and supported by novel volumetric measurements of chaos terrain deposits and intervening void spaces, that the geometry of martian chaoses is best explained by depressurization and compaction of an underlying confined aquifer. Block size distributions are incompatible with magma chamber collapse analog experiments. We show that sedimentary fill in chaos basins is inhomogeneously distributed, with layers thickening towards the chaos center, as in terrestrial sedimentary basins. The relationship between fracture block thickness and area is explained by the same power law that describes fracture spacing and layer thickness in weak terrestrial sandstones. The presence of some chaoses with blocks that are higher than surrounding plains implies repressurization of some sub-chaos aquifers. Hesperian-aged water or ice may remain within ∼1–3 km of the surface beneath these landforms.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"426 ","pages":"Article 116377"},"PeriodicalIF":2.5,"publicationDate":"2024-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142703710","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 : 2024-11-17DOI: 10.1016/j.icarus.2024.116371
Rose-Marie Baland , Valerio Filice , Sébastien Le Maistre , Antony Trinh , Marie Yseboodt , Tim Van Hoolst
Following the discovery of several ocean worlds in the solar system, and the selection of Uranus as the highest priority objective by the Planetary Science and Astrobiology Decadal Survey 2023-2032, the five largest moons of Uranus (Miranda, Ariel, Umbriel, Titania and Oberon) have been receiving renewed attention as they may also harbor a subsurface ocean. We assess how rotation measurements could help confirm the internal differentiation of the bodies and detect internal oceans if any. Because of the time-varying gravitational torque of Uranus on the flattened shape of its synchronous satellites, the latter librate with respect to their mean rotation and precess with a non zero obliquity. For a range of interior models with a rocky core surrounded by a hydrosphere, either solid or divided into an outer ice shell with a liquid ocean underneath, we compute their diurnal libration amplitude and obliquity. We find that if the Uranian satellites were two-layer solid bodies, libration measurement accuracies from around 0.25 m for Oberon to around 6 m for Miranda would rule out the possibility of homogeneous interiors. In combination with independent estimates of the mean moment of inertia (MOI), libration measurements could also be used to detect the presence of an ocean, the measurement precision required for this depending on the actual value of the libration amplitude. To compute the obliquity, we first build series for the orbital precession of all five satellites with a secular perturbations model. With the exception of Miranda, we show that due to the mutual gravitational interactions between the satellites, the obliquity of the large Uranian moons exhibits relatively large periodic variations around the mean value. We find that an obliquity measurement accuracy from around 1 m for Ariel to around 400 m for Oberon can rule out the homogeneous case. The presence of an internal global ocean could allow a resonant amplification of the obliquity, facilitating its detection. If no such resonance occurs, the obliquity would be almost indistinguishable from that expected for a solid body. The effect of tidal deformations on the rotation of the small to medium-sized Uranian moons is showed to be limited. Librations would be reduced by up to 10% and obliquity increased by up to 15% for Titania and Oberon, the effects being negligible for Miranda.
{"title":"Librations and obliquity of the largest moons of Uranus","authors":"Rose-Marie Baland , Valerio Filice , Sébastien Le Maistre , Antony Trinh , Marie Yseboodt , Tim Van Hoolst","doi":"10.1016/j.icarus.2024.116371","DOIUrl":"10.1016/j.icarus.2024.116371","url":null,"abstract":"<div><div>Following the discovery of several ocean worlds in the solar system, and the selection of Uranus as the highest priority objective by the Planetary Science and Astrobiology Decadal Survey 2023-2032, the five largest moons of Uranus (Miranda, Ariel, Umbriel, Titania and Oberon) have been receiving renewed attention as they may also harbor a subsurface ocean. We assess how rotation measurements could help confirm the internal differentiation of the bodies and detect internal oceans if any. Because of the time-varying gravitational torque of Uranus on the flattened shape of its synchronous satellites, the latter librate with respect to their mean rotation and precess with a non zero obliquity. For a range of interior models with a rocky core surrounded by a hydrosphere, either solid or divided into an outer ice shell with a liquid ocean underneath, we compute their diurnal libration amplitude and obliquity. We find that if the Uranian satellites were two-layer solid bodies, libration measurement accuracies from around 0.25 m for Oberon to around 6 m for Miranda would rule out the possibility of homogeneous interiors. In combination with independent estimates of the mean moment of inertia (MOI), libration measurements could also be used to detect the presence of an ocean, the measurement precision required for this depending on the actual value of the libration amplitude. To compute the obliquity, we first build series for the orbital precession of all five satellites with a secular perturbations model. With the exception of Miranda, we show that due to the mutual gravitational interactions between the satellites, the obliquity of the large Uranian moons exhibits relatively large periodic variations around the mean value. We find that an obliquity measurement accuracy from around 1 m for Ariel to around 400 m for Oberon can rule out the homogeneous case. The presence of an internal global ocean could allow a resonant amplification of the obliquity, facilitating its detection. If no such resonance occurs, the obliquity would be almost indistinguishable from that expected for a solid body. The effect of tidal deformations on the rotation of the small to medium-sized Uranian moons is showed to be limited. Librations would be reduced by up to 10% and obliquity increased by up to 15% for Titania and Oberon, the effects being negligible for Miranda.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"426 ","pages":"Article 116371"},"PeriodicalIF":2.5,"publicationDate":"2024-11-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142702605","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 : 2024-11-15DOI: 10.1016/j.icarus.2024.116353
N. Le Becq , S.J. Conway , B. Jabaud , G. Tobie , R. Artoni
<div><div>We report on the widespread occurence of talus on cerean crater walls using Dawn framing camera images. This is unexpected for a planetary body with no atmosphere like Ceres since the dominant process in crater degradation was expected to be topographic diffusion associated with impact gardening, like on the Moon or Mercury. To investigate why talus deposits are so common, and whether they could be related to the particular nature of Ceres’ ice-rich crust, we mapped them over the entire surface and studied their morphological characteristics. We classified the features into three different types, indicating their degree of preservation. Our results show that there is no trend between the total surface area of talus (whatever their degree of preservation) and latitude or longitude. However, we found that talus deposits tend to be observed within deep and young impact craters, and that certain craters expose a particularly large surface area of talus deposits: Dantu, Ninsar, Occator, Kupalo and Juling craters. It was also noted that well-preserved talus have a larger surface area than more degraded ones, and have <span><math><mo>≈</mo></math></span>20 % more consolidated outcrops per km<span><math><msup><mrow></mrow><mrow><mn>2</mn></mrow></msup></math></span>. Age estimates from crater size frequency distributions for the host craters completed these observations, giving a mean age of <span><math><mrow><mn>2</mn><msubsup><mrow><mn>0</mn></mrow><mrow><mo>−</mo><mn>4</mn></mrow><mrow><mo>+</mo><mn>4</mn></mrow></msubsup></mrow></math></span> Ma for the craters hosting the more preserved talus deposits, and <span><math><mrow><mn>28</mn><msubsup><mrow><mn>0</mn></mrow><mrow><mo>−</mo><mn>8</mn></mrow><mrow><mo>+</mo><mn>8</mn></mrow></msubsup></mrow></math></span> Ma for the craters hosting the more degraded ones. By studying the slope of the talus deposits, we obtained a value of the angle of repose of the cerean regolith: 34.5°<span><math><mo>±</mo></math></span> 2.8°. We also found that the talus facing the poles are approximately 5°steeper than those facing the equator, have an 18 % larger surface area, and exhibit three times as many outcrops compared to talus on crater walls facing other directions. This suggests that the degradation of outcrops, the source of the material making up the scree, is sensitive to insolation. If we assume that the outcrops are made cohesive by the ice they contain, then we can conclude that sublimation of this ice leads to their fragmentation, at the origin of the talus material. We suggest that outcrop wall retreat due to ice sublimation feeding talus slopes is a predominant process in the earlier phase of crater degradation on Ceres supplanting impact gardening and topographic diffusion for some tens of million years. Once the maximum extent of the talus is reached, the progressively reduced debris production leads to a decreasing talus activity. Impact gardening then takes over and talus deposits are slo
{"title":"A new model of crater degradation on Ceres involving ice sublimation and talus formation","authors":"N. Le Becq , S.J. Conway , B. Jabaud , G. Tobie , R. Artoni","doi":"10.1016/j.icarus.2024.116353","DOIUrl":"10.1016/j.icarus.2024.116353","url":null,"abstract":"<div><div>We report on the widespread occurence of talus on cerean crater walls using Dawn framing camera images. This is unexpected for a planetary body with no atmosphere like Ceres since the dominant process in crater degradation was expected to be topographic diffusion associated with impact gardening, like on the Moon or Mercury. To investigate why talus deposits are so common, and whether they could be related to the particular nature of Ceres’ ice-rich crust, we mapped them over the entire surface and studied their morphological characteristics. We classified the features into three different types, indicating their degree of preservation. Our results show that there is no trend between the total surface area of talus (whatever their degree of preservation) and latitude or longitude. However, we found that talus deposits tend to be observed within deep and young impact craters, and that certain craters expose a particularly large surface area of talus deposits: Dantu, Ninsar, Occator, Kupalo and Juling craters. It was also noted that well-preserved talus have a larger surface area than more degraded ones, and have <span><math><mo>≈</mo></math></span>20 % more consolidated outcrops per km<span><math><msup><mrow></mrow><mrow><mn>2</mn></mrow></msup></math></span>. Age estimates from crater size frequency distributions for the host craters completed these observations, giving a mean age of <span><math><mrow><mn>2</mn><msubsup><mrow><mn>0</mn></mrow><mrow><mo>−</mo><mn>4</mn></mrow><mrow><mo>+</mo><mn>4</mn></mrow></msubsup></mrow></math></span> Ma for the craters hosting the more preserved talus deposits, and <span><math><mrow><mn>28</mn><msubsup><mrow><mn>0</mn></mrow><mrow><mo>−</mo><mn>8</mn></mrow><mrow><mo>+</mo><mn>8</mn></mrow></msubsup></mrow></math></span> Ma for the craters hosting the more degraded ones. By studying the slope of the talus deposits, we obtained a value of the angle of repose of the cerean regolith: 34.5°<span><math><mo>±</mo></math></span> 2.8°. We also found that the talus facing the poles are approximately 5°steeper than those facing the equator, have an 18 % larger surface area, and exhibit three times as many outcrops compared to talus on crater walls facing other directions. This suggests that the degradation of outcrops, the source of the material making up the scree, is sensitive to insolation. If we assume that the outcrops are made cohesive by the ice they contain, then we can conclude that sublimation of this ice leads to their fragmentation, at the origin of the talus material. We suggest that outcrop wall retreat due to ice sublimation feeding talus slopes is a predominant process in the earlier phase of crater degradation on Ceres supplanting impact gardening and topographic diffusion for some tens of million years. Once the maximum extent of the talus is reached, the progressively reduced debris production leads to a decreasing talus activity. Impact gardening then takes over and talus deposits are slo","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"428 ","pages":"Article 116353"},"PeriodicalIF":2.5,"publicationDate":"2024-11-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142745841","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 : 2024-11-12DOI: 10.1016/j.icarus.2024.116373
Lukas Wueller , James W. Head , Erica R. Jawin , Thomas Heyer , Harald Hiesinger , Carolyn H. van der Bogert
We examine the characteristics and relationships of Lineated Valley Fill (LVF) and Lobate Debris Aprons (LDA) in Mamers Valles on Mars, a ∼950 km-long fretted valley at the dichotomy boundary. The relationships and distinctions between these glacial landforms are established by detailed analysis of LDA/LVF morphology, topography, and related features are assessed to understand their origin and modification. We document the transition from unconfined LDA to compressed and folded LVF and vice versa, implying that LDA and LVF are intimately related in morphology and mode of origin. Linear LDA dominate Mamers Valles, originating from alcoves, theater-like remnant crater rims, and tributary valleys, while circumferential LDA are arrayed around isolated mesas. Narrow valley areas display the convergence of lobes originating from either side, forming parallel linear ridges that deform into complex folds and become LVF, typically in a local and regional downvalley direction. In contrast, when LVF flows out of a topographically confined area, the material forms a piedmont-like LDA. Thus, local topography is the primary factor in determining whether a deposit will appear LVF-like, LDA-like, or have characteristics of both. Superimposed crater morphology and ground-penetrating radar data suggest the current presence of subsurface ice protected by ∼15–20 m of sublimation lag deposits, with minimal deformation and flow since superposed crater formation. Regional integration leads to the interpretation that the LDA-LVF exposures and ice entry points into the fretted valleys represent the waning stages of a more widespread regional Amazonian plateau glacial landsystem that occupied fretted terrain valleys formed earlier in the Late Noachian-Early Hesperian.
{"title":"Relationships between lobate debris aprons and lineated valley fill on Mars: Evidence for an extensive Amazonian valley glacial landsystem in Mamers Valles","authors":"Lukas Wueller , James W. Head , Erica R. Jawin , Thomas Heyer , Harald Hiesinger , Carolyn H. van der Bogert","doi":"10.1016/j.icarus.2024.116373","DOIUrl":"10.1016/j.icarus.2024.116373","url":null,"abstract":"<div><div>We examine the characteristics and relationships of Lineated Valley Fill (LVF) and Lobate Debris Aprons (LDA) in Mamers Valles on Mars, a ∼950 km-long fretted valley at the dichotomy boundary. The relationships and distinctions between these glacial landforms are established by detailed analysis of LDA/LVF morphology, topography, and related features are assessed to understand their origin and modification. We document the transition from unconfined LDA to compressed and folded LVF and vice versa, implying that LDA and LVF are intimately related in morphology and mode of origin. Linear LDA dominate Mamers Valles, originating from alcoves, theater-like remnant crater rims, and tributary valleys, while circumferential LDA are arrayed around isolated mesas. Narrow valley areas display the convergence of lobes originating from either side, forming parallel linear ridges that deform into complex folds and become LVF, typically in a local and regional downvalley direction. In contrast, when LVF flows out of a topographically confined area, the material forms a piedmont-like LDA. Thus, local topography is the primary factor in determining whether a deposit will appear LVF-like, LDA-like, or have characteristics of both. Superimposed crater morphology and ground-penetrating radar data suggest the current presence of subsurface ice protected by ∼15–20 m of sublimation lag deposits, with minimal deformation and flow since superposed crater formation. Regional integration leads to the interpretation that the LDA-LVF exposures and ice entry points into the fretted valleys represent the waning stages of a more widespread regional Amazonian plateau glacial landsystem that occupied fretted terrain valleys formed earlier in the Late Noachian-Early Hesperian.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"426 ","pages":"Article 116373"},"PeriodicalIF":2.5,"publicationDate":"2024-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142653243","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 : 2024-11-09DOI: 10.1016/j.icarus.2024.116366
Tobias Hoffmann , Marco Micheli , Juan Luis Cano , Maxime Devogèle , Davide Farnocchia , Petr Pravec , Peter Vereš , Björn Poppe
Photometric measurements allow the determination of an asteroid’s absolute magnitude, which often represents the sole means to infer its size. Photometric observations can be obtained in a variety of filters that can be unique to a specific observatory. Those observations are then calibrated into specific bands with respect to reference star catalogs. In order to combine all the different measurements for evaluation, photometric observations need to be converted to a common band, typically V-band. Current band-correction schemes in use by IAU’s Minor Planet Center (MPC), JPL’s Center for Near Earth Object Studies (CNEOS) and ESA’s NEO Coordination Centre (NEOCC) use average correction values for the apparent magnitude derived from photometry of asteroids as the corrections are dependent on the typically unknown spectrum of the object to be corrected. By statistically analyzing the photometric residuals of asteroids, we develop a new photometric correction scheme that does not only consider the band, but also accounts for reference catalog and observatory. We analyzed nearly 500 000 observations submitted to the MPC from 468 asteroids with published and independently determined high confidence and values. We describe a new statistical photometry correction scheme for asteroid observations with debiased corrections. Testing this scheme on a reference group of asteroids, we see a 36% reduction in the photometric residuals. Moreover, the new scheme leads to a more accurate and debiased determination of the - magnitude system and, in turn, to more reliable inferred sizes. We discuss the significant shift in the corrections with this “DePhOCUS” debiasing system, its limitations, and the impact for photometric and physical properties of all asteroids, especially Near-Earth Objects.
通过光度测量可以确定小行星的绝对星等，这通常是推断其大小的唯一方法。光度观测可以通过特定天文台特有的各种滤光片获得。然后根据参考星表将这些观测数据校准到特定的波段中。为了将所有不同的测量结果结合起来进行评估，需要将光度观测数据转换到一个共同的波段，通常是 V 波段。国际天文学联合会的小行星中心（MPC）、JPL 的近地天体研究中心（CNEOS）和欧空局的近地天体协调中心（NEOCC）目前使用的波段校正方案使用的是小行星光度测量得出的视星等平均校正值，因为校正值取决于待校正天体通常未知的光谱。通过统计分析小行星的测光残差，我们开发了一种新的测光校正方案，它不仅考虑了波段，还考虑了参考星表和观测站。我们分析了 468 颗小行星提交给 MPC 的近 500 000 次观测数据，这些小行星的 H 值和 G 值都是已公布并独立确定的高置信度值。我们描述了一种新的统计光度校正方案，用于小行星观测的去偏校正。在一组参考小行星上测试该方案后，我们发现测光残差降低了 36%。此外，新方案还能更准确地确定H-G星等系统的偏差，进而推断出更可靠的大小。我们将讨论这种 "DePhOCUS "除杂系统在校正方面的显著变化、它的局限性以及对所有小行星，尤其是近地天体的光度和物理特性的影响。
{"title":"Debiasing astro-photometric observations with corrections using statistics (DePhOCUS)","authors":"Tobias Hoffmann , Marco Micheli , Juan Luis Cano , Maxime Devogèle , Davide Farnocchia , Petr Pravec , Peter Vereš , Björn Poppe","doi":"10.1016/j.icarus.2024.116366","DOIUrl":"10.1016/j.icarus.2024.116366","url":null,"abstract":"<div><div>Photometric measurements allow the determination of an asteroid’s absolute magnitude, which often represents the sole means to infer its size. Photometric observations can be obtained in a variety of filters that can be unique to a specific observatory. Those observations are then calibrated into specific bands with respect to reference star catalogs. In order to combine all the different measurements for evaluation, photometric observations need to be converted to a common band, typically V-band. Current band-correction schemes in use by IAU’s Minor Planet Center (MPC), JPL’s Center for Near Earth Object Studies (CNEOS) and ESA’s NEO Coordination Centre (NEOCC) use average correction values for the apparent magnitude derived from photometry of asteroids as the corrections are dependent on the typically unknown spectrum of the object to be corrected. By statistically analyzing the photometric residuals of asteroids, we develop a new photometric correction scheme that does not only consider the band, but also accounts for reference catalog and observatory. We analyzed nearly 500<!--> <!-->000 observations submitted to the MPC from 468 asteroids with published and independently determined high confidence <span><math><mi>H</mi></math></span> and <span><math><mi>G</mi></math></span> values. We describe a new statistical photometry correction scheme for asteroid observations with debiased corrections. Testing this scheme on a reference group of asteroids, we see a 36% reduction in the photometric residuals. Moreover, the new scheme leads to a more accurate and debiased determination of the <span><math><mi>H</mi></math></span>-<span><math><mi>G</mi></math></span> magnitude system and, in turn, to more reliable inferred sizes. We discuss the significant shift in the corrections with this “DePhOCUS” debiasing system, its limitations, and the impact for photometric and physical properties of all asteroids, especially Near-Earth Objects.</div></div>","PeriodicalId":13199,"journal":{"name":"Icarus","volume":"426 ","pages":"Article 116366"},"PeriodicalIF":2.5,"publicationDate":"2024-11-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142703709","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}
扫码关注我们
求助内容：
应助结果提醒方式：
京公网安备 11010802042870号