Neptune’s external mean-motion resonances play an important role in sculpting the observed population of trans-Neptunian objects (TNOs). The population of scattering TNOs is known to “stick” to Neptune's resonances while evolving in semimajor axis (a), though simulations show that resonance sticking is less prevalent at a ≳ 200–250 au. Here we present an extensive numerical exploration of the strengths of Neptune's resonances for scattering TNOs with perihelion distances q = 33 au. We show that the drop-off in resonance sticking for the large a scattering TNOs is not a generic feature of scattering dynamics but can instead be attributed to the specific configuration of Neptune and Uranus in our solar system. In simulations with just Uranus removed from the giant planet system, Neptune's resonances are strong in the scattering population out to at least ∼300 au. Uranus and Neptune are near a 2:1 period ratio, and the variations in Neptune's orbit resulting from this near-resonance are responsible for destabilizing Neptune's resonances for high-e TNO orbits beyond the ∼20:1 resonance at a ≈ 220 au. Direct interactions between Uranus and the scattering population are responsible for slightly weakening Neptune's closer-in resonances. In simulations where Neptune and Uranus are placed in their mutual 2:1 resonance, we see almost no stable libration of scattering particles in Neptune's external resonances. Our results have important implications for how the strengths of Neptune's distant resonances varied during the epoch of planet migration when the Neptune–Uranus period ratio was evolving. These strength variations likely affected the distant scattering, resonant, and detached TNO populations.
海王星的外部平均运动共振在形成观测到的跨海王星天体（TNOs）群方面起着重要作用。众所周知，在半长轴（a）的演化过程中，散射的 TNO 物体群会 "粘附 "在海王星的共振上，不过模拟结果表明，共振粘附在 ≳ 200-250 au 时并不那么普遍。在这里，我们对近日点距离 q = 33 au 的散射 TNO 的海王星共振强度进行了广泛的数值探索。我们的研究表明，大a散射TNOs共振粘性的下降并不是散射动力学的一般特征，而是由于海王星和天王星在太阳系中的特殊构造造成的。在只将天王星从巨行星系统中移除的模拟中，海王星的共振在至少 ∼300 au 范围内的散射群体中是很强的。天王星和海王星的周期比接近 2:1，这种近共振导致海王星轨道的变化，从而破坏了海王星在 ≈ 220 au 处的∼20:1 共振之外的高 e TNO 轨道共振的稳定性。天王星和散射群之间的直接相互作用会稍微削弱海王星的近距离共振。在海王星和天王星处于2:1共振的模拟中，我们发现海王星外部共振中几乎没有稳定的散射粒子天平动。我们的研究结果对海王星-天王星周期比演变的行星迁移时代海王星遥远共振的强度如何变化具有重要意义。这些强度变化很可能会影响到遥远的散射、共振和分离的尘埃粒子群。
{"title":"Uranus’s Influence on Neptune’s Exterior Mean-motion Resonances","authors":"Severance Graham, Kathryn Volk","doi":"10.3847/psj/ad4707","DOIUrl":"https://doi.org/10.3847/psj/ad4707","url":null,"abstract":"Neptune’s external mean-motion resonances play an important role in sculpting the observed population of trans-Neptunian objects (TNOs). The population of scattering TNOs is known to “stick” to Neptune's resonances while evolving in semimajor axis (<italic toggle=\"yes\">a</italic>), though simulations show that resonance sticking is less prevalent at <italic toggle=\"yes\">a</italic> ≳ 200–250 au. Here we present an extensive numerical exploration of the strengths of Neptune's resonances for scattering TNOs with perihelion distances <italic toggle=\"yes\">q</italic> = 33 au. We show that the drop-off in resonance sticking for the large <italic toggle=\"yes\">a</italic> scattering TNOs is not a generic feature of scattering dynamics but can instead be attributed to the specific configuration of Neptune and Uranus in our solar system. In simulations with just Uranus removed from the giant planet system, Neptune's resonances are strong in the scattering population out to at least ∼300 au. Uranus and Neptune are near a 2:1 period ratio, and the variations in Neptune's orbit resulting from this near-resonance are responsible for destabilizing Neptune's resonances for high-<italic toggle=\"yes\">e</italic> TNO orbits beyond the ∼20:1 resonance at <italic toggle=\"yes\">a</italic> ≈ 220 au. Direct interactions between Uranus and the scattering population are responsible for slightly weakening Neptune's closer-in resonances. In simulations where Neptune and Uranus are placed in their mutual 2:1 resonance, we see almost no stable libration of scattering particles in Neptune's external resonances. Our results have important implications for how the strengths of Neptune's distant resonances varied during the epoch of planet migration when the Neptune–Uranus period ratio was evolving. These strength variations likely affected the distant scattering, resonant, and detached TNO populations.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"26 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504696","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Proton auroras are widely observed on the dayside of Mars, identified as a significant intensity enhancement in the hydrogen Lyα (121.6 nm) emission at altitudes of ∼110 and 150 km. Solar wind protons penetrating as energetic neutral atoms into Mars’ thermosphere are thought to be primarily responsible for these auroras. Recent observations of spatially localized “patchy” proton auroras suggest a possible direct deposition of protons into Mars’ atmosphere during unstable solar wind conditions. Improving our understanding of proton auroras is therefore important for characterizing the interaction of the solar wind with Mars’ atmosphere. Here, we develop a first purely data-driven model of proton auroras using Mars Atmosphere and Volatile Evolution (MAVEN) in situ observations and limb scans of Lyα emissions between 2014 and 2022. We train an artificial neural network that reproduces individual Lyα intensities and relative Lyα peak intensity enhancements with Pearson correlations of ∼94% and ∼60% respectively for the test data, along with a faithful reconstruction of the shape of the observed altitude profiles of Lyα emission. By performing a Shapley Additive Explanations (SHAP) analysis, we find that solar zenith angle, solar longitude, CO2 atmosphere variability, solar wind speed, and temperature are the most important features for the modeled Lyα peak intensity enhancements. Additionally, we find that the modeled peak intensity enhancements are high for early local-time hours, particularly near polar latitudes, and the induced magnetic fields are weaker. Through SHAP analysis, we also identify the influence of biases in the training data and interdependences between the measurements used for the modeling, and an improvement of those aspects can significantly improve the performance and applicability of the ANN model.
{"title":"An Explainable Deep-learning Model of Proton Auroras on Mars","authors":"Dattaraj B. Dhuri, Dimitra Atri, Ahmed AlHantoobi","doi":"10.3847/psj/ad45ff","DOIUrl":"https://doi.org/10.3847/psj/ad45ff","url":null,"abstract":"Proton auroras are widely observed on the dayside of Mars, identified as a significant intensity enhancement in the hydrogen Ly<italic toggle=\"yes\">α</italic> (121.6 nm) emission at altitudes of ∼110 and 150 km. Solar wind protons penetrating as energetic neutral atoms into Mars’ thermosphere are thought to be primarily responsible for these auroras. Recent observations of spatially localized “patchy” proton auroras suggest a possible direct deposition of protons into Mars’ atmosphere during unstable solar wind conditions. Improving our understanding of proton auroras is therefore important for characterizing the interaction of the solar wind with Mars’ atmosphere. Here, we develop a first purely data-driven model of proton auroras using Mars Atmosphere and Volatile Evolution (MAVEN) in situ observations and limb scans of Ly<italic toggle=\"yes\">α</italic> emissions between 2014 and 2022. We train an artificial neural network that reproduces individual Ly<italic toggle=\"yes\">α</italic> intensities and relative Ly<italic toggle=\"yes\">α</italic> peak intensity enhancements with Pearson correlations of ∼94% and ∼60% respectively for the test data, along with a faithful reconstruction of the shape of the observed altitude profiles of Ly<italic toggle=\"yes\">α</italic> emission. By performing a Shapley Additive Explanations (SHAP) analysis, we find that solar zenith angle, solar longitude, CO<sub>2</sub> atmosphere variability, solar wind speed, and temperature are the most important features for the modeled Ly<italic toggle=\"yes\">α</italic> peak intensity enhancements. Additionally, we find that the modeled peak intensity enhancements are high for early local-time hours, particularly near polar latitudes, and the induced magnetic fields are weaker. Through SHAP analysis, we also identify the influence of biases in the training data and interdependences between the measurements used for the modeling, and an improvement of those aspects can significantly improve the performance and applicability of the ANN model.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"96 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504697","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Juan A. Sanchez, Vishnu Reddy, Audrey Thirouin, William F. Bottke, Theodore Kareta, Mario De Florio, Benjamin N. L. Sharkey, Adam Battle, David C. Cantillo, Neil Pearson
The study of small (<300 m) near-Earth objects (NEOs) is important because they are more closely related than larger objects to the precursors of meteorites that fall on Earth. Collisions of these bodies with Earth are also more frequent. Although such collisions cannot produce massive extinction events, they can still produce significant local damage. Here we present the results of a photometric and spectroscopic survey of small NEOs that include near-infrared spectra of 84 objects with a mean diameter of 126 m and photometric data of 59 objects with a mean diameter of 87 m. We found that S-complex asteroids are the most abundant among the NEOs, comprising ∼66% of the sample. Most asteroids in the S-complex were found to have compositions consistent with LL-chondrites. Our study revealed the existence of NEOs with spectral characteristics similar to those in the S-complex but that could be hidden within the C- or X-complex due to their weak absorption bands. We suggest that the presence of metal or shock darkening could be responsible for the attenuation of the absorption bands. These objects have been grouped into a new subclass within the S-complex called Sx-types. The dynamical modeling showed that 83% of the NEOs escaped from the ν6 resonance, 16% from the 3:1, and just 1% from the 5:2 resonance. Lightcurves and rotational periods were derived from the photometric data. No clear trend between the axis ratio and the absolute magnitude or rotational period of the NEOs was found.
{"title":"The Population of Small Near-Earth Objects: Composition, Source Regions, and Rotational Properties","authors":"Juan A. Sanchez, Vishnu Reddy, Audrey Thirouin, William F. Bottke, Theodore Kareta, Mario De Florio, Benjamin N. L. Sharkey, Adam Battle, David C. Cantillo, Neil Pearson","doi":"10.3847/psj/ad445f","DOIUrl":"https://doi.org/10.3847/psj/ad445f","url":null,"abstract":"The study of small (<300 m) near-Earth objects (NEOs) is important because they are more closely related than larger objects to the precursors of meteorites that fall on Earth. Collisions of these bodies with Earth are also more frequent. Although such collisions cannot produce massive extinction events, they can still produce significant local damage. Here we present the results of a photometric and spectroscopic survey of small NEOs that include near-infrared spectra of 84 objects with a mean diameter of 126 m and photometric data of 59 objects with a mean diameter of 87 m. We found that S-complex asteroids are the most abundant among the NEOs, comprising ∼66% of the sample. Most asteroids in the S-complex were found to have compositions consistent with LL-chondrites. Our study revealed the existence of NEOs with spectral characteristics similar to those in the S-complex but that could be hidden within the C- or X-complex due to their weak absorption bands. We suggest that the presence of metal or shock darkening could be responsible for the attenuation of the absorption bands. These objects have been grouped into a new subclass within the S-complex called Sx-types. The dynamical modeling showed that 83% of the NEOs escaped from the <italic toggle=\"yes\">ν</italic>\u0000<sub>6</sub> resonance, 16% from the 3:1, and just 1% from the 5:2 resonance. Lightcurves and rotational periods were derived from the photometric data. No clear trend between the axis ratio and the absolute magnitude or rotational period of the NEOs was found.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"13 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141504698","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Catherine E. Regan, Andrew J. Coates, Mark Lester, Anne Wellbrock, Geraint H. Jones, Beatriz Sánchez-Cano, Philippe Garnier, Richard P. Haythornthwaite, Dikshita Meggi, Rudy A. Frahm and Mats Holmström
Mars's magnetosphere is a sensitive system, varying due to external and internal factors, such as solar wind conditions and crustal magnetic fields. A signature of this influence can be seen in the position of two boundaries; the bow shock and the induced magnetospheric boundary (IMB). The bow shock moves closer to Mars during times of high solar activity, and both the bow shock and IMB bulge away from Mars over crustal magnetic fields in the southern hemisphere. This study investigates whether large-scale atmospheric events at Mars have any signature in these two magnetic boundaries, by investigating the 2007 storm. The 2007 global storm lasted for several months and increased atmospheric temperatures and densities of both water vapor and carbon dioxide in the atmosphere, leading to an increase in atmospheric escape. Using Mars Express, we identified boundary locations before, during, and after the event, and compared these to modeled boundary locations and areographical locations on Mars. We find that, while it is unclear whether the bow shock position is impacted by the storm, the IMB location does change significantly, despite the orbital bias introduced by Mars Express. The terminator distance for the IMB peaks at longitudes 0°–40° and 310°–360°, leaving a depression around 180° longitude, where the boundary usually extends to higher altitudes due to the crustal magnetic fields. We suggest this may be due to the confinement of ionospheric plasma over crustal fields preventing mixing with the dust, creating a dip in ionospheric pressure here.
{"title":"Effects of the 2007 Martian Global Dust Storm on Boundary Positions in the Induced Magnetosphere","authors":"Catherine E. Regan, Andrew J. Coates, Mark Lester, Anne Wellbrock, Geraint H. Jones, Beatriz Sánchez-Cano, Philippe Garnier, Richard P. Haythornthwaite, Dikshita Meggi, Rudy A. Frahm and Mats Holmström","doi":"10.3847/psj/ad4116","DOIUrl":"https://doi.org/10.3847/psj/ad4116","url":null,"abstract":"Mars's magnetosphere is a sensitive system, varying due to external and internal factors, such as solar wind conditions and crustal magnetic fields. A signature of this influence can be seen in the position of two boundaries; the bow shock and the induced magnetospheric boundary (IMB). The bow shock moves closer to Mars during times of high solar activity, and both the bow shock and IMB bulge away from Mars over crustal magnetic fields in the southern hemisphere. This study investigates whether large-scale atmospheric events at Mars have any signature in these two magnetic boundaries, by investigating the 2007 storm. The 2007 global storm lasted for several months and increased atmospheric temperatures and densities of both water vapor and carbon dioxide in the atmosphere, leading to an increase in atmospheric escape. Using Mars Express, we identified boundary locations before, during, and after the event, and compared these to modeled boundary locations and areographical locations on Mars. We find that, while it is unclear whether the bow shock position is impacted by the storm, the IMB location does change significantly, despite the orbital bias introduced by Mars Express. The terminator distance for the IMB peaks at longitudes 0°–40° and 310°–360°, leaving a depression around 180° longitude, where the boundary usually extends to higher altitudes due to the crustal magnetic fields. We suggest this may be due to the confinement of ionospheric plasma over crustal fields preventing mixing with the dust, creating a dip in ionospheric pressure here.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"95 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-06-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141257302","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tim Lister, Cora Constantinescu, William Ryan, Eileen Ryan, Edward Gomez, Liz Phillips, Agata Rożek, Helen Usher, Brian P. Murphy, Joseph Chatelain and Sarah Greenstreet
The world’s first planetary defense test mission was carried out in late 2022 by NASA’s Double Asteroid Redirection Test (DART) mission. The main DART spacecraft, which was accompanied by the ASI-provided LICIACube cubesat, intentionally impacted Dimorphos, the smaller secondary of the near-Earth object binary system (65803) Didymos, on 2022 September 26. The impact released a large amount of ejecta, which, combined with the spacecraft’s momentum, produced the observed 33 ± 1 minute period change that was subsequently observed from ground-based telescopes. The DART mission, in addition to having successfully changed the orbital period of Dimorphos, also activated the asteroid as a result of the impact but under known conditions, unlike other impacts on asteroids. We have conducted long-term monitoring over 5 months following the impact with the Las Cumbres Observatory Global Telescope (LCOGT) network and Magdalena Ridge Observatory (MRO). This was supplemented by almost 3 months of more sparsely sampled data, primarily from educational users of the LCOGT network during the period from 2022 July 5 to 2022 September 25, prior to the impact date of 2022 September 26. Here we report the observations of the Didymos system and DART impact ejecta with the telescopes of the LCOGT network from T+1.93 days to T+151.3 days after impact, and we study the evolving morphology of the ejecta cloud and evolving tail over the entire length of the data set. In addition, we combined these intensive data sets with the earlier sparse observations over the ∼90 days prior to impact to derive a new disk-integrated phase function model using the H, G1, G2 parameterization.
{"title":"Long-term Monitoring of Didymos with the LCOGT Network and MRO after the DART Impact","authors":"Tim Lister, Cora Constantinescu, William Ryan, Eileen Ryan, Edward Gomez, Liz Phillips, Agata Rożek, Helen Usher, Brian P. Murphy, Joseph Chatelain and Sarah Greenstreet","doi":"10.3847/psj/ad4345","DOIUrl":"https://doi.org/10.3847/psj/ad4345","url":null,"abstract":"The world’s first planetary defense test mission was carried out in late 2022 by NASA’s Double Asteroid Redirection Test (DART) mission. The main DART spacecraft, which was accompanied by the ASI-provided LICIACube cubesat, intentionally impacted Dimorphos, the smaller secondary of the near-Earth object binary system (65803) Didymos, on 2022 September 26. The impact released a large amount of ejecta, which, combined with the spacecraft’s momentum, produced the observed 33 ± 1 minute period change that was subsequently observed from ground-based telescopes. The DART mission, in addition to having successfully changed the orbital period of Dimorphos, also activated the asteroid as a result of the impact but under known conditions, unlike other impacts on asteroids. We have conducted long-term monitoring over 5 months following the impact with the Las Cumbres Observatory Global Telescope (LCOGT) network and Magdalena Ridge Observatory (MRO). This was supplemented by almost 3 months of more sparsely sampled data, primarily from educational users of the LCOGT network during the period from 2022 July 5 to 2022 September 25, prior to the impact date of 2022 September 26. Here we report the observations of the Didymos system and DART impact ejecta with the telescopes of the LCOGT network from T+1.93 days to T+151.3 days after impact, and we study the evolving morphology of the ejecta cloud and evolving tail over the entire length of the data set. In addition, we combined these intensive data sets with the earlier sparse observations over the ∼90 days prior to impact to derive a new disk-integrated phase function model using the H, G1, G2 parameterization.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"58 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141197576","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Tomas Kohout, Maurizio Pajola, Assi-Johanna Soini, Alice Lucchetti, Arto Luttinen, Alexia Duchêne, Naomi Murdoch, Robert Luther, Nancy L. Chabot, Sabina D. Raducan, Paul Sánchez, Olivier S. Barnouin and Andrew S. Rivkin
The ∼200 m s−1 impact of a single 400 kg Bjurböle L/LL ordinary chondrite meteorite onto sea ice resulted in the catastrophic disruption of the projectile. This resulted in a significant fraction of decimeter-sized fragments that exhibit power-law cumulative size and mass distributions. This size range is underrepresented in impact experiments and asteroid boulder studies. The Bjurböle projectile fragments share similarities in shape (sphericity and roughness at small and large scales) with asteroid boulders. However, the mean aspect ratio (3D measurement) and apparent aspect ratio (2D measurement) of the Bjurböle fragments is 0.83 and 0.77, respectively, indicating that Bjurböle fragments are more equidimensional compared to both fragments produced in smaller-scale impact experiments and asteroid boulders. These differences may be attributed either to the fragment source (projectile versus target), to the high porosity and low strength of Bjurböle, to the lower impact velocity compared with typical asteroid collision velocities, or potentially to fragment erosion during sea sediment penetration or cleaning.
{"title":"Impact Disruption of Bjurböle Porous Chondritic Projectile","authors":"Tomas Kohout, Maurizio Pajola, Assi-Johanna Soini, Alice Lucchetti, Arto Luttinen, Alexia Duchêne, Naomi Murdoch, Robert Luther, Nancy L. Chabot, Sabina D. Raducan, Paul Sánchez, Olivier S. Barnouin and Andrew S. Rivkin","doi":"10.3847/psj/ad4266","DOIUrl":"https://doi.org/10.3847/psj/ad4266","url":null,"abstract":"The ∼200 m s−1 impact of a single 400 kg Bjurböle L/LL ordinary chondrite meteorite onto sea ice resulted in the catastrophic disruption of the projectile. This resulted in a significant fraction of decimeter-sized fragments that exhibit power-law cumulative size and mass distributions. This size range is underrepresented in impact experiments and asteroid boulder studies. The Bjurböle projectile fragments share similarities in shape (sphericity and roughness at small and large scales) with asteroid boulders. However, the mean aspect ratio (3D measurement) and apparent aspect ratio (2D measurement) of the Bjurböle fragments is 0.83 and 0.77, respectively, indicating that Bjurböle fragments are more equidimensional compared to both fragments produced in smaller-scale impact experiments and asteroid boulders. These differences may be attributed either to the fragment source (projectile versus target), to the high porosity and low strength of Bjurböle, to the lower impact velocity compared with typical asteroid collision velocities, or potentially to fragment erosion during sea sediment penetration or cleaning.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"67 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141188410","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Marc Rovira-Navarro, Isamu Matsuyama and Alexander Berne
Body tides reveal information about planetary interiors and affect their evolution. Most models to compute body tides rely on the assumption of a spherically symmetric interior. However, several processes can lead to lateral variations of interior properties. We present a new spectral method to compute the tidal response of laterally heterogeneous bodies. Compared to previous spectral methods, our approach is not limited to small-amplitude lateral variations; compared to finite element codes, this approach is more computationally efficient. While the tidal response of a spherically symmetric body has the same wavelength as the tidal force; lateral heterogeneities produce an additional tidal response with a spectra that depends on the spatial pattern of such variations. For Mercury, the Moon, and Io, the amplitude of this signal is as high as 1%–10% of the main tidal response for long-wavelength shear modulus variations higher than ∼10% of the mean shear modulus. For Europa, Ganymede, and Enceladus, shell-thickness variations of 50% of the mean shell thickness can cause an additional signal of ∼1% and ∼10% for the Jovian moons and Encelaudus, respectively. Future missions, such as BepiColombo and JUICE, might measure these signals. Lateral variations of viscosity affect the distribution of tidal heating. This can drive the thermal evolution of tidally active bodies and affect the distribution of active regions.
{"title":"A Spectral Method to Compute the Tides of Laterally Heterogeneous Bodies","authors":"Marc Rovira-Navarro, Isamu Matsuyama and Alexander Berne","doi":"10.3847/psj/ad381f","DOIUrl":"https://doi.org/10.3847/psj/ad381f","url":null,"abstract":"Body tides reveal information about planetary interiors and affect their evolution. Most models to compute body tides rely on the assumption of a spherically symmetric interior. However, several processes can lead to lateral variations of interior properties. We present a new spectral method to compute the tidal response of laterally heterogeneous bodies. Compared to previous spectral methods, our approach is not limited to small-amplitude lateral variations; compared to finite element codes, this approach is more computationally efficient. While the tidal response of a spherically symmetric body has the same wavelength as the tidal force; lateral heterogeneities produce an additional tidal response with a spectra that depends on the spatial pattern of such variations. For Mercury, the Moon, and Io, the amplitude of this signal is as high as 1%–10% of the main tidal response for long-wavelength shear modulus variations higher than ∼10% of the mean shear modulus. For Europa, Ganymede, and Enceladus, shell-thickness variations of 50% of the mean shell thickness can cause an additional signal of ∼1% and ∼10% for the Jovian moons and Encelaudus, respectively. Future missions, such as BepiColombo and JUICE, might measure these signals. Lateral variations of viscosity affect the distribution of tidal heating. This can drive the thermal evolution of tidally active bodies and affect the distribution of active regions.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"44 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141197795","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Norbert Schörghofer, Jean-Pierre Williams and Erwan Mazarico
Lunar cold traps are defined by extremely low sublimation rates, such that water ice could have accumulated in them. Here time-averaged sublimation rates are calculated for the north polar region of the Moon based on over 14 years of Diviner surface temperature measurements. Data for each spatial pixel are binned according to subsolar (diurnal) and ecliptic (seasonal) longitude. The cold trap area poleward of 80°N is about 32% larger when defined by a time-average sublimation rate instead of by peak temperature. Apparently sunlit cold traps are identified, e.g., in Lenard Crater, where modeling of direct illumination reveals that the Sun briefly rises above the horizon each Draconic year. The true cold trap area is smaller than what can be determined from Diviner data. Also presented are north polar maps for the potential sublimation rate of relic buried ice and for subsurface cold trapping.
{"title":"Lunar North Polar Cold Traps Based on Diurnally and Seasonally Varying Temperatures","authors":"Norbert Schörghofer, Jean-Pierre Williams and Erwan Mazarico","doi":"10.3847/psj/ad49a8","DOIUrl":"https://doi.org/10.3847/psj/ad49a8","url":null,"abstract":"Lunar cold traps are defined by extremely low sublimation rates, such that water ice could have accumulated in them. Here time-averaged sublimation rates are calculated for the north polar region of the Moon based on over 14 years of Diviner surface temperature measurements. Data for each spatial pixel are binned according to subsolar (diurnal) and ecliptic (seasonal) longitude. The cold trap area poleward of 80°N is about 32% larger when defined by a time-average sublimation rate instead of by peak temperature. Apparently sunlit cold traps are identified, e.g., in Lenard Crater, where modeling of direct illumination reveals that the Sun briefly rises above the horizon each Draconic year. The true cold trap area is smaller than what can be determined from Diviner data. Also presented are north polar maps for the potential sublimation rate of relic buried ice and for subsurface cold trapping.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"17 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141188469","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Alexander E. Thelen, Conor A. Nixon, Martin A. Cordiner, Emmanuel Lellouch, Sandrine Vinatier, Nicholas A. Teanby, Bryan Butler, Steven B. Charnley, Richard G. Cosentino, Katherine de Kleer, Patrick G. J. Irwin, Mark A. Gurwell, Zbigniew Kisiel and Raphael Moreno
Titan’s atmospheric composition and dynamical state have previously been studied over numerous epochs by both ground- and space-based facilities. However, stratospheric measurements remain sparse during Titan’s northern summer and fall. The lack of seasonal symmetry in observations of Titan’s temperature field and chemical abundances raises questions about the nature of the middle atmosphere’s meridional circulation and evolution over Titan’s 29 yr seasonal cycle that can only be answered through long-term monitoring campaigns. Here, we present maps of Titan’s stratospheric temperature, acetonitrile (or methyl cyanide; CH3CN) abundance, and monodeuterated methane (CH3D) abundance following Titan’s northern summer solstice obtained with Band 9 (∼0.43 mm) Atacama Large Millimeter/submillimeter Array observations. We find that increasing temperatures toward high southern latitudes, currently in winter, resemble those observed during Titan’s northern winter by the Cassini mission. Acetonitrile abundances have changed significantly since previous (sub)millimeter observations, and we find that the species is now highly concentrated at high southern latitudes. The stratospheric CH3D content is found to range between 4 and 8 ppm in these observations, and we infer the CH4 abundance to vary between ∼0.9% and 1.6% through conversion with previously measured D/H values. A global value of CH4 = 1.15% was retrieved, lending further evidence to the temporal and spatial variability of Titan’s stratospheric methane when compared with previous measurements. Additional observations are required to determine the cause and magnitude of stratospheric enhancements in methane during these poorly understood seasons on Titan.
{"title":"Observations of Titan’s Stratosphere during Northern Summer: Temperatures, CH3CN and CH3D Abundances","authors":"Alexander E. Thelen, Conor A. Nixon, Martin A. Cordiner, Emmanuel Lellouch, Sandrine Vinatier, Nicholas A. Teanby, Bryan Butler, Steven B. Charnley, Richard G. Cosentino, Katherine de Kleer, Patrick G. J. Irwin, Mark A. Gurwell, Zbigniew Kisiel and Raphael Moreno","doi":"10.3847/psj/ad47bd","DOIUrl":"https://doi.org/10.3847/psj/ad47bd","url":null,"abstract":"Titan’s atmospheric composition and dynamical state have previously been studied over numerous epochs by both ground- and space-based facilities. However, stratospheric measurements remain sparse during Titan’s northern summer and fall. The lack of seasonal symmetry in observations of Titan’s temperature field and chemical abundances raises questions about the nature of the middle atmosphere’s meridional circulation and evolution over Titan’s 29 yr seasonal cycle that can only be answered through long-term monitoring campaigns. Here, we present maps of Titan’s stratospheric temperature, acetonitrile (or methyl cyanide; CH3CN) abundance, and monodeuterated methane (CH3D) abundance following Titan’s northern summer solstice obtained with Band 9 (∼0.43 mm) Atacama Large Millimeter/submillimeter Array observations. We find that increasing temperatures toward high southern latitudes, currently in winter, resemble those observed during Titan’s northern winter by the Cassini mission. Acetonitrile abundances have changed significantly since previous (sub)millimeter observations, and we find that the species is now highly concentrated at high southern latitudes. The stratospheric CH3D content is found to range between 4 and 8 ppm in these observations, and we infer the CH4 abundance to vary between ∼0.9% and 1.6% through conversion with previously measured D/H values. A global value of CH4 = 1.15% was retrieved, lending further evidence to the temporal and spatial variability of Titan’s stratospheric methane when compared with previous measurements. Additional observations are required to determine the cause and magnitude of stratospheric enhancements in methane during these poorly understood seasons on Titan.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"74 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141188470","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ryan T. Walker, Michael K. Barker, Erwan Mazarico, Xiaoli Sun, Gregory A. Neumann, David E. Smith, James W. Head and Maria T. Zuber
Examining the reflectance of the Moon's surface across a broad range of viewing geometries through photometric analysis can reveal physical and geological properties of its regolith. Since 2013 December, the Lunar Orbiter Laser Altimeter (LOLA) on board the Lunar Reconnaissance Orbiter (LRO) has been operating as a near-infrared (1064 nm) passive radiometer when its laser is turned off. We present a new analysis of this data set spanning roughly 8 yr and covering the surface up to high latitudes in both hemispheres. We apply semiempirical phase functions to find a lower photometric slope and a narrower opposition effect for the highlands than the maria, consistent with theoretical expectations given the higher albedo of the highlands. Examining various geological properties at global scales shows that, in the highlands, iron abundance (FeO) and optical maturity (OMAT) are the dominant factors affecting the phase function, with a smaller influence from surface slope. In the maria, FeO is the dominant factor, with smaller influences from OMAT, surface slope, and TiO2. Submicroscopic iron abundance (SMFe) has a similar effect to OMAT in both highlands and maria. Analysis at specific sites, including the Reiner Gamma swirl and several silicic anomalies, indicates that the phase functions are consistent with the global data for similar FeO and OMAT. Thermophysical properties inferred from surface temperature observations by the Diviner Lunar Radiometer Experiment on board LRO do not affect the 1064 nm phase function, possibly due to a difference between their depth scale and LOLA's sensing depth.
{"title":"Near-infrared Photometry of the Moon's Surface with Passive Radiometry from the Lunar Orbiter Laser Altimeter (LOLA)","authors":"Ryan T. Walker, Michael K. Barker, Erwan Mazarico, Xiaoli Sun, Gregory A. Neumann, David E. Smith, James W. Head and Maria T. Zuber","doi":"10.3847/psj/ad4467","DOIUrl":"https://doi.org/10.3847/psj/ad4467","url":null,"abstract":"Examining the reflectance of the Moon's surface across a broad range of viewing geometries through photometric analysis can reveal physical and geological properties of its regolith. Since 2013 December, the Lunar Orbiter Laser Altimeter (LOLA) on board the Lunar Reconnaissance Orbiter (LRO) has been operating as a near-infrared (1064 nm) passive radiometer when its laser is turned off. We present a new analysis of this data set spanning roughly 8 yr and covering the surface up to high latitudes in both hemispheres. We apply semiempirical phase functions to find a lower photometric slope and a narrower opposition effect for the highlands than the maria, consistent with theoretical expectations given the higher albedo of the highlands. Examining various geological properties at global scales shows that, in the highlands, iron abundance (FeO) and optical maturity (OMAT) are the dominant factors affecting the phase function, with a smaller influence from surface slope. In the maria, FeO is the dominant factor, with smaller influences from OMAT, surface slope, and TiO2. Submicroscopic iron abundance (SMFe) has a similar effect to OMAT in both highlands and maria. Analysis at specific sites, including the Reiner Gamma swirl and several silicic anomalies, indicates that the phase functions are consistent with the global data for similar FeO and OMAT. Thermophysical properties inferred from surface temperature observations by the Diviner Lunar Radiometer Experiment on board LRO do not affect the 1064 nm phase function, possibly due to a difference between their depth scale and LOLA's sensing depth.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"45 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-05-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141165507","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：