On the Moon, the surface morphology at the scale of meters and tens of meters is typically smooth and subdued due to regolith gardening. Sharp, “crisp,” meter-scale morphologic features are observed only where the regolith is either thin or recently disturbed. Such crisp morphologies are typically created by geologically recent meteoritic impacts of different scales. The prominent exception is so-called irregular mare patches (IMPs), rare small features of debated origin. We report here on the discovery of previously unknown crisp immature morphological features (named “spiders” due to their central circular region and radiating “legs”) not related to impacts and even more rare. The spiders are meters-deep depressions with near-radial chutes open toward the center which make an incipient dendritic pattern 50–80 m in diameter. All spiders found thus far occur in clusters in the same region in Mare Tranquillitatis in the immediate proximity to small IMPs. We interpret spiders as the result of an energetic granular flow of the regolith draining into shallow subsurface voids following the sudden collapse of the roofs of the voids. Regolith gardening destroys the spiders’ legs rapidly, on a timescale of a million years. If the entrance into the subsurface void remains unclogged, a spider appears to evolve into a pit; otherwise it evolves into a gentle depression and finally disappears. Our interpretation of spiders provides a consistent explanation of all of their features, occurrence settings, and associations.
{"title":"“Spiders” on the Moon: Morphological Evidence for Geologically Recent Regolith Drainage into Subsurface Voids","authors":"Mikhail A. Kreslavsky, James W. Head","doi":"10.3847/psj/ad2e09","DOIUrl":"https://doi.org/10.3847/psj/ad2e09","url":null,"abstract":"On the Moon, the surface morphology at the scale of meters and tens of meters is typically smooth and subdued due to regolith gardening. Sharp, “crisp,” meter-scale morphologic features are observed only where the regolith is either thin or recently disturbed. Such crisp morphologies are typically created by geologically recent meteoritic impacts of different scales. The prominent exception is so-called irregular mare patches (IMPs), rare small features of debated origin. We report here on the discovery of previously unknown crisp immature morphological features (named “spiders” due to their central circular region and radiating “legs”) not related to impacts and even more rare. The spiders are meters-deep depressions with near-radial chutes open toward the center which make an incipient dendritic pattern 50–80 m in diameter. All spiders found thus far occur in clusters in the same region in Mare Tranquillitatis in the immediate proximity to small IMPs. We interpret spiders as the result of an energetic granular flow of the regolith draining into shallow subsurface voids following the sudden collapse of the roofs of the voids. Regolith gardening destroys the spiders’ legs rapidly, on a timescale of a million years. If the entrance into the subsurface void remains unclogged, a spider appears to evolve into a pit; otherwise it evolves into a gentle depression and finally disappears. Our interpretation of spiders provides a consistent explanation of all of their features, occurrence settings, and associations.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"18 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140610085","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}
Adam Battle, Vishnu Reddy, Juan A. Sanchez, Benjamin Sharkey, Tanner Campbell, Paul Chodas, Al Conrad, Daniel P. Engelhart, James Frith, Roberto Furfaro, Davide Farnocchia, Olga Kuhn, Neil Pearson, Barry Rothberg, Christian Veillet, Richard Wainscoat
Since the dawn of the Space Age, hundreds of payloads have been launched into heliocentric space. As near-Earth object (NEO) surveys search deeper for small asteroids, more artificial objects in heliocentric orbits are being discovered. We now face a challenge to identify the true nature of these objects and avoid contaminating the NEO catalog. Here, we present the methods used to characterize one such object. 2020 SO was discovered by the Pan-STARRS1 survey on 2020 September 17. Originally classified as a NEO, the object’s artificial nature became evident due to its low velocity relative to Earth and solar radiation pressure affecting its orbit about the Sun. Based on a backward propagation of its orbit, 2020 SO is thought to be a Centaur rocket body (R/B) from the launch of the Surveyor 2 mission to the Moon. We characterized 2020 SO using a range of ground-based optical and near-infrared telescopes to constrain its true nature. We find that its reflectance spectrum is consistent with that of other Centaur R/B launched during a similar time frame, and we identify 1.4, 1.7, and 2.3 μm absorption bands consistent with polyvinyl fluoride used on the aft bulkhead radiation shield exterior of Centaur-D R/B at the time.
自太空时代开始以来，已经向日心空间发射了数百个有效载荷。随着近地天体（NEO）探测对小行星的深入搜寻，更多位于日心轨道上的人造天体被发现。我们现在面临的挑战是如何识别这些天体的真实性质并避免污染近地天体目录。在此，我们将介绍用于描述这样一个天体特征的方法。2020 SO是在2020年9月17日由Pan-STARRS1巡天发现的。该天体最初被归类为近地天体，但由于其相对于地球的速度较低，且太阳辐射压力影响了其围绕太阳的轨道，因此其人造性质变得十分明显。根据其轨道的后向传播，2020 SO 被认为是一个半人马座火箭体（R/B），来自向月球发射的勘测者 2 号任务。我们利用一系列地面光学和近红外望远镜对 2020 SO 进行了特征描述，以确定其真实性质。我们发现它的反射光谱与在类似时间段发射的其他半人马R/B的光谱一致，我们还发现了1.4、1.7和2.3微米吸收带，与当时半人马-D R/B尾部隔板防辐射罩外部使用的聚氟乙烯一致。
{"title":"Challenges in Identifying Artificial Objects in the Near-Earth Object Population: Spectral Characterization of 2020 SO","authors":"Adam Battle, Vishnu Reddy, Juan A. Sanchez, Benjamin Sharkey, Tanner Campbell, Paul Chodas, Al Conrad, Daniel P. Engelhart, James Frith, Roberto Furfaro, Davide Farnocchia, Olga Kuhn, Neil Pearson, Barry Rothberg, Christian Veillet, Richard Wainscoat","doi":"10.3847/psj/ad3078","DOIUrl":"https://doi.org/10.3847/psj/ad3078","url":null,"abstract":"Since the dawn of the Space Age, hundreds of payloads have been launched into heliocentric space. As near-Earth object (NEO) surveys search deeper for small asteroids, more artificial objects in heliocentric orbits are being discovered. We now face a challenge to identify the true nature of these objects and avoid contaminating the NEO catalog. Here, we present the methods used to characterize one such object. 2020 SO was discovered by the Pan-STARRS1 survey on 2020 September 17. Originally classified as a NEO, the object’s artificial nature became evident due to its low velocity relative to Earth and solar radiation pressure affecting its orbit about the Sun. Based on a backward propagation of its orbit, 2020 SO is thought to be a Centaur rocket body (R/B) from the launch of the Surveyor 2 mission to the Moon. We characterized 2020 SO using a range of ground-based optical and near-infrared telescopes to constrain its true nature. We find that its reflectance spectrum is consistent with that of other Centaur R/B launched during a similar time frame, and we identify 1.4, 1.7, and 2.3 <italic toggle=\"yes\">μ</italic>m absorption bands consistent with polyvinyl fluoride used on the aft bulkhead radiation shield exterior of Centaur-D R/B at the time.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"12 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140610088","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}
Maryse Napoleoni, Lucía Hortal Sánchez, Nozair Khawaja, Bernd Abel, Christopher R. Glein, Jon K. Hillier, Frank Postberg
Characterizing the geochemistry of Europa and Enceladus is a key step for astrobiology investigations looking for evidence of life in their subsurface oceans. Transition metals with several oxidation states, such as iron, may be tracers of the oxidation state of icy ocean moon interiors. Their detection, as well as the characterization of their oxidation states, on the moons’ (plume) ice grains would bring valuable new information about the geochemistry of both the subsurface oceans and surface processes. Impact ionization mass spectrometers such as the SUDA instrument on board Europa Clipper can analyze ice grains ejected from icy moons’ surfaces and detect ocean-derived salts therein. Here we record mass spectra analogs for SUDA using the Laser Induced Liquid Beam Ion Desorption technique for Fe2+ and Fe3+ salts (both sulfates and chlorides). We show that impact ionization mass spectrometers have the capability to detect and differentiate ferrous (Fe2+) from ferric (Fe3+) ions in both cation and anion modes owing to their tendency to form distinct ionic complexes with characteristic spectral features. Peaks bearing Fe3+, such as [Fe3+ (OH)2]+ and [Fe3+ (OH)a Clb]−, are particularly important to discriminate between the two oxidation states of iron in the sample. The recorded analog spectra may allow the characterization of the oxidation state of the oceans of Europa and Enceladus with implications for hydrothermal processes and potential metabolic pathways for life forms in their subsurface oceans.
{"title":"Probing the Oxidation State of Ocean Worlds with SUDA: Fe (ii) and Fe (iii) in Ice Grains","authors":"Maryse Napoleoni, Lucía Hortal Sánchez, Nozair Khawaja, Bernd Abel, Christopher R. Glein, Jon K. Hillier, Frank Postberg","doi":"10.3847/psj/ad2462","DOIUrl":"https://doi.org/10.3847/psj/ad2462","url":null,"abstract":"Characterizing the geochemistry of Europa and Enceladus is a key step for astrobiology investigations looking for evidence of life in their subsurface oceans. Transition metals with several oxidation states, such as iron, may be tracers of the oxidation state of icy ocean moon interiors. Their detection, as well as the characterization of their oxidation states, on the moons’ (plume) ice grains would bring valuable new information about the geochemistry of both the subsurface oceans and surface processes. Impact ionization mass spectrometers such as the SUDA instrument on board Europa Clipper can analyze ice grains ejected from icy moons’ surfaces and detect ocean-derived salts therein. Here we record mass spectra analogs for SUDA using the Laser Induced Liquid Beam Ion Desorption technique for Fe<sup>2+</sup> and Fe<sup>3+</sup> salts (both sulfates and chlorides). We show that impact ionization mass spectrometers have the capability to detect and differentiate ferrous (Fe<sup>2+</sup>) from ferric (Fe<sup>3+</sup>) ions in both cation and anion modes owing to their tendency to form distinct ionic complexes with characteristic spectral features. Peaks bearing Fe<sup>3+</sup>, such as [Fe<sup>3+</sup> (OH)<sub>2</sub>]<sup>+</sup> and [Fe<sup>3+</sup> (OH)<sub>\u0000<italic toggle=\"yes\">a</italic>\u0000</sub> Cl<sub>\u0000<italic toggle=\"yes\">b</italic>\u0000</sub>]<sup>−</sup>, are particularly important to discriminate between the two oxidation states of iron in the sample. The recorded analog spectra may allow the characterization of the oxidation state of the oceans of Europa and Enceladus with implications for hydrothermal processes and potential metabolic pathways for life forms in their subsurface oceans.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"11 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140610028","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}
Edgard G. Rivera-Valentín, Caleb I. Fassett, Brett W. Denevi, Heather M. Meyer, Catherine D. Neish, Gareth A. Morgan, Joshua T. S. Cahill, Angela M. Stickle, G. Wesley Patterson
One of the youngest features on the Moon is Tycho, an 85 km diameter impact crater with a vast ray system that spans much of the lunar nearside. As such, it serves as an important stratigraphic marker for the Moon. One of Tycho’s longest rays crosses the South Pole, where it intersects several candidate landing sites for NASA’s Artemis III mission, which intends to return new lunar samples. Identification of ray-related effects are thus important to understand the provenance of collected material. To help contextualize sampling strategies, here we characterize the South Pole–crossing Tycho ray using monostatic S-band radar observations from the Lunar Reconnaissance Orbiter’s Miniature Radio Frequency instrument. We found that the ray is a ∼15 km wide radar-bright feature extending at least ∼1600 km from Tycho. Polarimetric analysis revealed that the measured radar backscatter is consistent with a terrain enhanced in centimeter-to-decimeter-scale scatterers. Moreover, we found that the abundance of these scatterers likely decreases with distance from the primary crater, suggesting there may be less Tycho-disturbed material, in particular, poleward of 85°S, where the candidate landing sites are located. Nevertheless, we identified craters along the ray and, importantly, within the Haworth candidate landing site that exhibit secondary crater characteristics, such as radar-bright, asymmetric ejecta deposits. We showed, based on solar illumination and topographic slopes, that the likely Tycho-related secondaries within Haworth are accessible by landed missions. Exploration of this site may thus directly sample Tycho-disturbed material, including a nearby permanently shadowed region, providing new insights into lunar surface processes.
蒂乔是月球上最年轻的地貌之一，它是一个直径为 85 公里的撞击坑，其巨大的射线系统横跨月球近侧的大部分区域。因此，它是月球重要的地层标记。蒂乔最长的射线之一穿过南极，与美国宇航局打算送回新月球样本的阿耳特弥斯三号任务的几个候选着陆点相交。因此，识别与射线有关的影响对于了解所采集材料的来源非常重要。为了帮助确定取样策略，我们在这里利用月球勘测轨道器的微型射频仪器进行的单静态 S 波段雷达观测，描述了穿越南极的第谷射线的特征。我们发现，该射线是一个宽 15 千米的雷达光亮特征，从第谷星至少延伸了 1600 千米。极坐标分析表明，测量到的雷达反向散射符合一个厘米到分米级散射体增强的地形。此外，我们还发现，这些散射体的数量可能会随着与原生环形山距离的增加而减少，这表明受第谷星干扰的物质可能较少，特别是在候选着陆点所在的南纬85°以北。尽管如此，我们还是发现了射线沿线的陨石坑，更重要的是，在霍沃斯候选着陆点内的陨石坑表现出了次级陨石坑的特征，如雷达亮度高、不对称的喷出物沉积。我们根据太阳光照和地形坡度表明，着陆任务可以进入哈沃斯内可能与泰乔相关的次级环形山。因此，对该地点的探索可以直接对蒂丘扰动物质进行取样，包括附近的永久阴影区，从而为了解月球表面过程提供新的视角。
{"title":"Mini-RF S-band Radar Characterization of a Lunar South Pole–crossing Tycho Ray: Implications for Sampling Strategies","authors":"Edgard G. Rivera-Valentín, Caleb I. Fassett, Brett W. Denevi, Heather M. Meyer, Catherine D. Neish, Gareth A. Morgan, Joshua T. S. Cahill, Angela M. Stickle, G. Wesley Patterson","doi":"10.3847/psj/ad320d","DOIUrl":"https://doi.org/10.3847/psj/ad320d","url":null,"abstract":"One of the youngest features on the Moon is Tycho, an 85 km diameter impact crater with a vast ray system that spans much of the lunar nearside. As such, it serves as an important stratigraphic marker for the Moon. One of Tycho’s longest rays crosses the South Pole, where it intersects several candidate landing sites for NASA’s Artemis III mission, which intends to return new lunar samples. Identification of ray-related effects are thus important to understand the provenance of collected material. To help contextualize sampling strategies, here we characterize the South Pole–crossing Tycho ray using monostatic <italic toggle=\"yes\">S</italic>-band radar observations from the Lunar Reconnaissance Orbiter’s Miniature Radio Frequency instrument. We found that the ray is a ∼15 km wide radar-bright feature extending at least ∼1600 km from Tycho. Polarimetric analysis revealed that the measured radar backscatter is consistent with a terrain enhanced in centimeter-to-decimeter-scale scatterers. Moreover, we found that the abundance of these scatterers likely decreases with distance from the primary crater, suggesting there may be less Tycho-disturbed material, in particular, poleward of 85°S, where the candidate landing sites are located. Nevertheless, we identified craters along the ray and, importantly, within the Haworth candidate landing site that exhibit secondary crater characteristics, such as radar-bright, asymmetric ejecta deposits. We showed, based on solar illumination and topographic slopes, that the likely Tycho-related secondaries within Haworth are accessible by landed missions. Exploration of this site may thus directly sample Tycho-disturbed material, including a nearby permanently shadowed region, providing new insights into lunar surface processes.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"69 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140610093","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}
Michael A. Velez, Kurt D. Retherford, Vincent Hue, Joshua A. Kammer, Tracy M. Becker, G. Randall Gladstone, Michael W. Davis, Thomas K. Greathouse, Philippa M. Molyneux, Shawn M. Brooks, Ujjwal Raut, Maarten H. Versteeg
Ultraviolet spectroscopy is a powerful method to study planetary surface composition through reflectance measurements, atmospheric composition through stellar/solar occultations, transits of other planetary bodies, and direct imaging of airglow and auroral emissions. The next generation of ultraviolet spectrographs (UVS) on board ESA’s Jupiter Icy Moons Explorer and NASA’s Europa Clipper missions will perform such measurements of Jupiter and its moons in the early 2030s. This work presents a compilation of a detailed UV stellar catalog, named Catalog of Ultraviolet Bright Stars (CUBS), of targets with high intensity in the 50–210 nm wavelength range with applications relevant to planetary spectroscopy. These applications include (1) planning and simulating occultations, including calibration measurements; (2) modeling starlight illumination of dark, nightside planetary surfaces primarily lit by the sky; and (3) studying the origin of diffuse Galactic UV light as mapped by existing data sets from Juno-UVS and others. CUBS includes observations from the International Ultraviolet Explorer (IUE) and additional information from the SIMBAD database. We have constructed model spectra at 0.1 nm resolution for almost 90,000 targets using interpolated Kurucz models (which have a resolution of 1 nm) and, when available, IUE spectra. CUBS also includes robust checks for agreement between the Kurucz models and the IUE data. We also present a tool for which our catalog can be used to identify the best candidates for stellar occultation observations, with applications for any UV instrument. We report on our methods for producing CUBS and discuss plans for its implementation during ongoing and upcoming planetary missions.
{"title":"Catalog of Ultraviolet Bright Stars: Strategies for UV Occultation Measurements, Planetary Illumination Modeling, and Sky Map Analyses Using Hybrid IUE-Kurucz Spectra","authors":"Michael A. Velez, Kurt D. Retherford, Vincent Hue, Joshua A. Kammer, Tracy M. Becker, G. Randall Gladstone, Michael W. Davis, Thomas K. Greathouse, Philippa M. Molyneux, Shawn M. Brooks, Ujjwal Raut, Maarten H. Versteeg","doi":"10.3847/psj/ad0e70","DOIUrl":"https://doi.org/10.3847/psj/ad0e70","url":null,"abstract":"Ultraviolet spectroscopy is a powerful method to study planetary surface composition through reflectance measurements, atmospheric composition through stellar/solar occultations, transits of other planetary bodies, and direct imaging of airglow and auroral emissions. The next generation of ultraviolet spectrographs (UVS) on board ESA’s Jupiter Icy Moons Explorer and NASA’s Europa Clipper missions will perform such measurements of Jupiter and its moons in the early 2030s. This work presents a compilation of a detailed UV stellar catalog, named Catalog of Ultraviolet Bright Stars (CUBS), of targets with high intensity in the 50–210 nm wavelength range with applications relevant to planetary spectroscopy. These applications include (1) planning and simulating occultations, including calibration measurements; (2) modeling starlight illumination of dark, nightside planetary surfaces primarily lit by the sky; and (3) studying the origin of diffuse Galactic UV light as mapped by existing data sets from Juno-UVS and others. CUBS includes observations from the International Ultraviolet Explorer (IUE) and additional information from the SIMBAD database. We have constructed model spectra at 0.1 nm resolution for almost 90,000 targets using interpolated Kurucz models (which have a resolution of 1 nm) and, when available, IUE spectra. CUBS also includes robust checks for agreement between the Kurucz models and the IUE data. We also present a tool for which our catalog can be used to identify the best candidates for stellar occultation observations, with applications for any UV instrument. We report on our methods for producing CUBS and discuss plans for its implementation during ongoing and upcoming planetary missions.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"20 2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140600275","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}
Andrew J. Ryan, Benjamin Rozitis, Daniel Pino Munoz, Kris J. Becker, Joshua P. Emery, Michael C. Nolan, Marc Bernacki, Marco Delbo, Catherine M. Elder, Matthew Siegler, Erica R. Jawin, Dathon R. Golish, Kevin J. Walsh, Christopher W. Haberle, Carina A. Bennett, Kenneth L. Edmundson, Victoria E. Hamilton, Phillip R. Christensen, Michael G. Daly, Dante S. Lauretta
The Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission recently returned a sample of rocks and dust collected from asteroid Bennu. We analyzed the highest-resolution thermal data obtained by the OSIRIS-REx Thermal Emission Spectrometer (OTES) to gain insight into the thermal and physical properties of the sampling site, including rocks that may have been sampled, and the immediately surrounding Hokioi Crater. After correcting the pointing of the OTES data sets, we find that OTES fortuitously observed two dark rocks moments before they were contacted by the spacecraft. We derived thermal inertias of 100–150 (±50) J m−2 K−1 s−1/2 for these two rocks—exceptionally low even compared with other previously analyzed dark rocks on Bennu (180–250 J m−2 K−1 s−1/2). Our simulations indicate that monolayer coatings of sand- to pebble-sized particles, as observed on one of these rocks, could significantly reduce the apparent thermal inertia and largely mask the properties of the substrate. However, the other low-thermal-inertia rock that was contacted is not obviously covered in particles. Moreover, this rock appears to have been partially crushed, and thus potentially sampled, by the spacecraft. We conclude that this rock may be highly fractured and that it should be sought in the returned sample to better understand its origin in Bennu’s parent body and the relationship between its thermal and physical properties.
{"title":"Rocks with Extremely Low Thermal Inertia at the OSIRIS-REx Sample Site on Asteroid Bennu","authors":"Andrew J. Ryan, Benjamin Rozitis, Daniel Pino Munoz, Kris J. Becker, Joshua P. Emery, Michael C. Nolan, Marc Bernacki, Marco Delbo, Catherine M. Elder, Matthew Siegler, Erica R. Jawin, Dathon R. Golish, Kevin J. Walsh, Christopher W. Haberle, Carina A. Bennett, Kenneth L. Edmundson, Victoria E. Hamilton, Phillip R. Christensen, Michael G. Daly, Dante S. Lauretta","doi":"10.3847/psj/ad2dff","DOIUrl":"https://doi.org/10.3847/psj/ad2dff","url":null,"abstract":"The Origins, Spectral Interpretation, Resource Identification, and Security–Regolith Explorer (OSIRIS-REx) mission recently returned a sample of rocks and dust collected from asteroid Bennu. We analyzed the highest-resolution thermal data obtained by the OSIRIS-REx Thermal Emission Spectrometer (OTES) to gain insight into the thermal and physical properties of the sampling site, including rocks that may have been sampled, and the immediately surrounding Hokioi Crater. After correcting the pointing of the OTES data sets, we find that OTES fortuitously observed two dark rocks moments before they were contacted by the spacecraft. We derived thermal inertias of 100–150 (±50) J m<sup>−2</sup> K<sup>−1</sup> s<sup>−1/2</sup> for these two rocks—exceptionally low even compared with other previously analyzed dark rocks on Bennu (180–250 J m<sup>−2</sup> K<sup>−1</sup> s<sup>−1/2</sup>). Our simulations indicate that monolayer coatings of sand- to pebble-sized particles, as observed on one of these rocks, could significantly reduce the apparent thermal inertia and largely mask the properties of the substrate. However, the other low-thermal-inertia rock that was contacted is not obviously covered in particles. Moreover, this rock appears to have been partially crushed, and thus potentially sampled, by the spacecraft. We conclude that this rock may be highly fractured and that it should be sought in the returned sample to better understand its origin in Bennu’s parent body and the relationship between its thermal and physical properties.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"65 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140600307","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}
P. H. Hasselmann, V. Della Corte, P. Pravec, S. Ieva, I. Gai, D. Perna, J. D. P. Deshapriya, E. Mazzotta-Epifani, E. Dotto, A. Zinzi, G. Poggiali, I. Bertini, A. Lucchetti, M. Pajola, J. Beccarelli, M. Dall’Ora, J.-Y. Li, S. L. Ivanovski, A. Rossi, J. R. Brucato, C. A. Thomas, O. Barnouin, J. M. Sunshine, A. S. Rivkin, M. Amoroso, A. Capannolo, S. Caporali, M. Ceresoli, G. Cremonese, R. T. Daly, G. Impresario, R. Lasagni-Manghi, M. Lavagna, D. Modenini, E. E. Palmer, P. Palumbo, S. Pirrotta, P. Tortora, M. Zannoni, G. Zanotti
On 2022 September 26, NASA's Double Asteroid Redirection Test (DART) successfully hit Dimorphos, the smaller companion of the binary system formed with the asteroid (65803) Didymos. Both the binary system and the impact event were imaged by the Light Italian Cubesat for Imaging of Asteroids, detached from DART 15 days before the impact. Images from the onboard LUKE red, green, and blue camera together with ground-based observations enabled the reconstruction of Didymos's brightness phase curve, with phase angles ranging from 2.35° to 107.7°. The opposition effect regime was studied using the exponential-linear equation, the “Shevchenko” function and the linear-by-parts model while the IAU-official HG1G2 magnitude system was applied to the full phase curve. The opposition effect indicates an unusual asteroid surface for an S type, with characteristics similar to M-type asteroids. While the HG1G2 parameters from the full phase curve place Didymos well among asteroids of the taxonomic C complex. Didymos’s phase curve parameters when compared to near-Earth asteroids are very close to the Q type (1862) Apollo, indicating possible depletion of fine submicrometric grains through resurfacing. Didymos's geometric albedo (0.15 ± 0.01) is reported to be 30%–45% smaller than the average geometric albedo for near-Earth S types (0.26 ± 0.04). We propose that Didymos might be an LL ordinary chondrite analog containing albedo-suppressing, shock-darkened/impact melt minerals that have undergone resurfacing processes in the past. A comparison with meteorites indicates that, less likely, Didymos could also contain materials analog to carbon-bearing brecciated L3 ordinary chondrites.
2022年9月26日，NASA的双小行星重定向试验（DART）成功撞击了与小行星（65803）Didymos形成的双星系统中较小的伴星Dimorphos。双小行星系统和撞击事件都由意大利小行星成像轻立方体卫星（Light Italian Cubesat for Imaging of Asteroids）进行了成像，该卫星在撞击发生前 15 天脱离了 DART。星载 LUKE 红、绿、蓝照相机拍摄的图像与地面观测数据相结合，重建了狄迪莫斯的亮度相位曲线，相位角从 2.35°到 107.7°不等。利用指数-线性方程、"舍甫琴科 "函数和逐部分线性模型对对冲效应机制进行了研究，同时将国际天文学联合会官方的 HG1G2 星等系统应用于完整的相位曲线。对立效应表明这颗 S 型小行星的表面很不寻常，具有类似于 M 型小行星的特征。而根据全相位曲线得出的 HG1G2 参数，迪迪莫斯在分类学上属于 C 型小行星。与近地小行星相比，迪迪莫斯的相位曲线参数非常接近于 Q 型（1862 年）阿波罗小行星，这表明亚微米级的细小颗粒可能在重铸过程中损耗殆尽。据报道，迪迪莫斯的几何反照率（0.15 ± 0.01）比近地 S 型小行星的平均几何反照率（0.26 ± 0.04）小 30%-45%。我们认为，迪迪莫斯可能是一种低地普通金刚石类似物，其中含有抑制反照率的冲击暗化/撞击熔融矿物，这些矿物在过去经历了重铺过程。与陨石的比较表明，迪迪莫斯也可能含有类似于含碳角砾化 L3 普通软玉的物质，但这种可能性较小。
{"title":"The Unusual Brightness Phase Curve of (65803) Didymos","authors":"P. H. Hasselmann, V. Della Corte, P. Pravec, S. Ieva, I. Gai, D. Perna, J. D. P. Deshapriya, E. Mazzotta-Epifani, E. Dotto, A. Zinzi, G. Poggiali, I. Bertini, A. Lucchetti, M. Pajola, J. Beccarelli, M. Dall’Ora, J.-Y. Li, S. L. Ivanovski, A. Rossi, J. R. Brucato, C. A. Thomas, O. Barnouin, J. M. Sunshine, A. S. Rivkin, M. Amoroso, A. Capannolo, S. Caporali, M. Ceresoli, G. Cremonese, R. T. Daly, G. Impresario, R. Lasagni-Manghi, M. Lavagna, D. Modenini, E. E. Palmer, P. Palumbo, S. Pirrotta, P. Tortora, M. Zannoni, G. Zanotti","doi":"10.3847/psj/ad2add","DOIUrl":"https://doi.org/10.3847/psj/ad2add","url":null,"abstract":"On 2022 September 26, NASA's Double Asteroid Redirection Test (DART) successfully hit Dimorphos, the smaller companion of the binary system formed with the asteroid (65803) Didymos. Both the binary system and the impact event were imaged by the Light Italian Cubesat for Imaging of Asteroids, detached from DART 15 days before the impact. Images from the onboard LUKE red, green, and blue camera together with ground-based observations enabled the reconstruction of Didymos's brightness phase curve, with phase angles ranging from 2.35° to 107.7°. The opposition effect regime was studied using the exponential-linear equation, the “Shevchenko” function and the linear-by-parts model while the IAU-official HG1G2 magnitude system was applied to the full phase curve. The opposition effect indicates an unusual asteroid surface for an S type, with characteristics similar to M-type asteroids. While the HG1G2 parameters from the full phase curve place Didymos well among asteroids of the taxonomic C complex. Didymos’s phase curve parameters when compared to near-Earth asteroids are very close to the Q type (1862) Apollo, indicating possible depletion of fine submicrometric grains through resurfacing. Didymos's geometric albedo (0.15 ± 0.01) is reported to be 30%–45% smaller than the average geometric albedo for near-Earth S types (0.26 ± 0.04). We propose that Didymos might be an LL ordinary chondrite analog containing albedo-suppressing, shock-darkened/impact melt minerals that have undergone resurfacing processes in the past. A comparison with meteorites indicates that, less likely, Didymos could also contain materials analog to carbon-bearing brecciated L3 ordinary chondrites.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"123 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140600409","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}
Jonathan P. Itcovitz, Auriol S. P. Rae, Thomas M. Davison, Gareth S. Collins, Oliver Shorttle
Large impacts onto young rocky planets may transform their compositions, creating highly reducing conditions at their surfaces and reintroducing highly siderophile metals to their mantles. Key to these processes is the availability of an impactor’s chemically reduced core material (metallic iron). It is, therefore, important to constrain how much of an impactor’s core remains accessible to a planet’s mantle/surface, how much is sequestered to its core, and how much escapes. Here, we present 3D simulations of such impact scenarios using the shock physics code iSALE to determine the fate of impactor iron. iSALE’s inclusion of material strength is vital in capturing the behavior of both solid and fluid components of the planet and thus characterizing iron sequestration to the core. We find that the mass fractions of impactor core material that accretes to the planet core (fcore) or escapes (fesc) can be readily parameterized as a function of a modified specific impact energy, with fcore>fesc for a wide set of impacts. These results differ from previous works that do not incorporate material strength. Our work shows that large impacts can place substantial reducing impactor core material in the mantles of young rocky planets. Impact-generated reducing atmospheres may thus be common for such worlds. However, through escape and sequestration to a planet’s core, large fractions of an impactor’s core can be geochemically hidden from a planet’s mantle. Consequently, geochemical estimates of late bombardments of planets based on mantle siderophile element abundances may be underestimates.
{"title":"The Distribution of Impactor Core Material During Large Impacts on Earth-like Planets","authors":"Jonathan P. Itcovitz, Auriol S. P. Rae, Thomas M. Davison, Gareth S. Collins, Oliver Shorttle","doi":"10.3847/psj/ad2ea4","DOIUrl":"https://doi.org/10.3847/psj/ad2ea4","url":null,"abstract":"Large impacts onto young rocky planets may transform their compositions, creating highly reducing conditions at their surfaces and reintroducing highly siderophile metals to their mantles. Key to these processes is the availability of an impactor’s chemically reduced core material (metallic iron). It is, therefore, important to constrain how much of an impactor’s core remains accessible to a planet’s mantle/surface, how much is sequestered to its core, and how much escapes. Here, we present 3D simulations of such impact scenarios using the shock physics code iSALE to determine the fate of impactor iron. iSALE’s inclusion of material strength is vital in capturing the behavior of both solid and fluid components of the planet and thus characterizing iron sequestration to the core. We find that the mass fractions of impactor core material that accretes to the planet core (<italic toggle=\"yes\">f</italic>\u0000<sub>core</sub>) or escapes (<italic toggle=\"yes\">f</italic>\u0000<sub>esc</sub>) can be readily parameterized as a function of a modified specific impact energy, with <inline-formula>\u0000<tex-math>\u0000<?CDATA ${f}_{mathrm{core}}gt {f}_{mathrm{esc}}$?>\u0000</tex-math>\u0000<mml:math overflow=\"scroll\"><mml:msub><mml:mrow><mml:mi>f</mml:mi></mml:mrow><mml:mrow><mml:mi>core</mml:mi></mml:mrow></mml:msub><mml:mo>></mml:mo><mml:msub><mml:mrow><mml:mi>f</mml:mi></mml:mrow><mml:mrow><mml:mi>esc</mml:mi></mml:mrow></mml:msub></mml:math>\u0000<inline-graphic xlink:href=\"psjad2ea4ieqn1.gif\" xlink:type=\"simple\"></inline-graphic>\u0000</inline-formula> for a wide set of impacts. These results differ from previous works that do not incorporate material strength. Our work shows that large impacts can place substantial reducing impactor core material in the mantles of young rocky planets. Impact-generated reducing atmospheres may thus be common for such worlds. However, through escape and sequestration to a planet’s core, large fractions of an impactor’s core can be geochemically hidden from a planet’s mantle. Consequently, geochemical estimates of late bombardments of planets based on mantle siderophile element abundances may be underestimates.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"53 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140600406","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}
William F. Bottke, David Vokrouhlický, David Nesvorný, Raphael Marschall, Alessandro Morbidelli, Rogerio Deienno, Simone Marchi, Michelle Kirchoff, Luke Dones, Harold F. Levison
The origins of the giant planet satellites are debated, with scenarios including formation from a protoplanetary disk, sequential assembly from massive rings, and recent accretion after major satellite–satellite collisions. Here, we test their predictions by simulating outer solar system bombardment and calculating the oldest surface ages on each moon. Our crater production model assumes the projectiles originated from a massive primordial Kuiper Belt (PKB) that experienced substantial changes from collisional evolution, which transformed its size frequency distribution into a wavy shape, and Neptune’s outward migration, which ejected most PKB objects onto destabilized orbits. The latter event also triggered an instability among the giant planets some tens of Myr after the solar nebula dispersed. We find all giant planet satellites are missing their earliest crater histories, with the likely source being impact resetting events. Iapetus, Hyperion, Phoebe, and Oberon have surface ages that are a few Myr to a few tens of Myr younger than when Neptune entered the PKB (i.e., they are 4.52–4.53 Gyr old). The remaining midsized satellites of Saturn and Uranus, as well as the small satellites located between Saturn’s rings and Dione, have surfaces that are younger still by many tens to many hundreds of Myr (4.1–4.5 Gyr old). A much wider range of surface ages are found for the large moons Callisto, Ganymede, Titan, and Europa (4.1, 3.4, 1.8, and 0.18 Gyr old, respectively). At present, we favor the midsized and larger moons forming within protoplanetary disks, with the other scenarios having several challenges to overcome.
{"title":"The Bombardment History of the Giant Planet Satellites","authors":"William F. Bottke, David Vokrouhlický, David Nesvorný, Raphael Marschall, Alessandro Morbidelli, Rogerio Deienno, Simone Marchi, Michelle Kirchoff, Luke Dones, Harold F. Levison","doi":"10.3847/psj/ad29f4","DOIUrl":"https://doi.org/10.3847/psj/ad29f4","url":null,"abstract":"The origins of the giant planet satellites are debated, with scenarios including formation from a protoplanetary disk, sequential assembly from massive rings, and recent accretion after major satellite–satellite collisions. Here, we test their predictions by simulating outer solar system bombardment and calculating the oldest surface ages on each moon. Our crater production model assumes the projectiles originated from a massive primordial Kuiper Belt (PKB) that experienced substantial changes from collisional evolution, which transformed its size frequency distribution into a wavy shape, and Neptune’s outward migration, which ejected most PKB objects onto destabilized orbits. The latter event also triggered an instability among the giant planets some tens of Myr after the solar nebula dispersed. We find all giant planet satellites are missing their earliest crater histories, with the likely source being impact resetting events. Iapetus, Hyperion, Phoebe, and Oberon have surface ages that are a few Myr to a few tens of Myr younger than when Neptune entered the PKB (i.e., they are 4.52–4.53 Gyr old). The remaining midsized satellites of Saturn and Uranus, as well as the small satellites located between Saturn’s rings and Dione, have surfaces that are younger still by many tens to many hundreds of Myr (4.1–4.5 Gyr old). A much wider range of surface ages are found for the large moons Callisto, Ganymede, Titan, and Europa (4.1, 3.4, 1.8, and 0.18 Gyr old, respectively). At present, we favor the midsized and larger moons forming within protoplanetary disks, with the other scenarios having several challenges to overcome.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"20 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140600513","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}
Ian Wong, Michael E. Brown, Joshua P. Emery, Richard P. Binzel, William M. Grundy, Simone Marchi, Audrey C. Martin, Keith S. Noll, Jessica M. Sunshine
We present observations obtained with the Near Infrared Spectrograph on JWST of the five Jupiter Trojans that will be visited by the Lucy spacecraft—the Patroclus–Menoetius binary, Eurybates, Orus, Leucus, and Polymele. The measured 1.7–5.3 μm reflectance spectra, which provide increased wavelength coverage, spatial resolution, and signal-to-noise ratio over previous ground-based spectroscopy, reveal several distinct absorption features. We detect a broad OH band centered at 3 μm that is most prominent on the less-red objects Eurybates, Patroclus–Menoetius, and Polymele. An additional absorption feature at 3.3–3.6 μm, indicative of aliphatic organics, is systematically deeper on the red objects Orus and Leucus. The collisional fragment Eurybates is unique in displaying an absorption band at 4.25 μm that we attribute to bound or trapped CO2. Comparisons with other solar system small bodies reveal broad similarities in the 2.7–3.6 μm bands with analogous features on Centaurs, Kuiper Belt objects (KBOs), and the active asteroid 238P. In the context of recent solar system evolution models, which posit that the Trojans initially formed in the outer solar system, the significant attenuation of the 2.7–3.6 μm absorption features on Trojans relative to KBOs may be the result of secondary thermal processing of the Trojans’ surfaces at the higher temperatures of the Jupiter region. The CO2 band manifested on the surface of Eurybates suggests that CO2 may be a major constituent in the bulk composition of Trojans, but resides in the subsurface or deeper interior and is largely obscured by refractory material that formed from the thermophysical processes that were activated during their inward migration.
{"title":"JWST Near-infrared Spectroscopy of the Lucy Jupiter Trojan Flyby Targets: Evidence for OH Absorption, Aliphatic Organics, and CO2","authors":"Ian Wong, Michael E. Brown, Joshua P. Emery, Richard P. Binzel, William M. Grundy, Simone Marchi, Audrey C. Martin, Keith S. Noll, Jessica M. Sunshine","doi":"10.3847/psj/ad2fc3","DOIUrl":"https://doi.org/10.3847/psj/ad2fc3","url":null,"abstract":"We present observations obtained with the Near Infrared Spectrograph on JWST of the five Jupiter Trojans that will be visited by the Lucy spacecraft—the Patroclus–Menoetius binary, Eurybates, Orus, Leucus, and Polymele. The measured 1.7–5.3 <italic toggle=\"yes\">μ</italic>m reflectance spectra, which provide increased wavelength coverage, spatial resolution, and signal-to-noise ratio over previous ground-based spectroscopy, reveal several distinct absorption features. We detect a broad OH band centered at 3 <italic toggle=\"yes\">μ</italic>m that is most prominent on the less-red objects Eurybates, Patroclus–Menoetius, and Polymele. An additional absorption feature at 3.3–3.6 <italic toggle=\"yes\">μ</italic>m, indicative of aliphatic organics, is systematically deeper on the red objects Orus and Leucus. The collisional fragment Eurybates is unique in displaying an absorption band at 4.25 <italic toggle=\"yes\">μ</italic>m that we attribute to bound or trapped CO<sub>2</sub>. Comparisons with other solar system small bodies reveal broad similarities in the 2.7–3.6 <italic toggle=\"yes\">μ</italic>m bands with analogous features on Centaurs, Kuiper Belt objects (KBOs), and the active asteroid 238P. In the context of recent solar system evolution models, which posit that the Trojans initially formed in the outer solar system, the significant attenuation of the 2.7–3.6 <italic toggle=\"yes\">μ</italic>m absorption features on Trojans relative to KBOs may be the result of secondary thermal processing of the Trojans’ surfaces at the higher temperatures of the Jupiter region. The CO<sub>2</sub> band manifested on the surface of Eurybates suggests that CO<sub>2</sub> may be a major constituent in the bulk composition of Trojans, but resides in the subsurface or deeper interior and is largely obscured by refractory material that formed from the thermophysical processes that were activated during their inward migration.","PeriodicalId":34524,"journal":{"name":"The Planetary Science Journal","volume":"55 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-04-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"140600772","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}
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