The enigmatic abundance of atomic hydrogen in Saturn's upper atmosphere
A planet's Lyman-{\alpha} (Ly{\alpha}) emission is sensitive to its thermospheric structure. Here, we report joint Hubble Space Telescope (HST) and Cassini cross-calibration observations of the Saturn Ly{\alpha} emission made two weeks before the Cassini grand finale. To investigate the long-te...
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description | A planet's Lyman-{\alpha} (Ly{\alpha}) emission is sensitive to its thermospheric structure. Here, we report joint Hubble Space Telescope (HST) and Cassini cross-calibration observations of the Saturn Ly{\alpha} emission made two weeks before the Cassini grand finale. To investigate the long-term Saturn Ly{\alpha} airglow observed by different ultraviolet instruments, we cross-correlate their calibration, finding that while the official Cassini/UVIS sensitivity should be lowered by ~75%, the Voyager 1/UVS sensitivities should be enhanced by ~20% at the Ly{\alpha} channels. This comparison also allowed us to discover a permanent feature of the Saturn disk Ly{\alpha} brightness that appears at all longitudes as a brightness excess (Ly{\alpha} bulge) of ~30% (~12{\sigma}) extending over the latitude range ~5-35N compared to the regions at equator and ~60N. This feature is confirmed by three distinct instruments between 1980 & 2017 in the Saturn north hemisphere. To analyze the Ly{\alpha} observations, we use a radiation transfer (RT) model of resonant scattering of solar and interplanetary Ly{\alpha} photons, and a latitude-dependent photochemistry model of the upper atmosphere constrained by occultation and remote-sensing observations. For each latitude, we show that the Ly{\alpha} observations are sensitive to the temperature profile in the upper stratosphere and lower thermosphere, thus providing useful information in a region of the atmosphere that is difficult to probe by other means. In the Saturn Ly{\alpha} bulge region, at latitudes between ~5 to ~35{\deg}, the observed brightening and line broadening support seasonal effects, variation of the temperature vertical profile, and potential superthermal atoms that require confirmation. |
doi_str_mv | 10.48550/arxiv.2311.14191 |
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Here, we report joint Hubble Space Telescope (HST) and Cassini cross-calibration observations of the Saturn Ly{\alpha} emission made two weeks before the Cassini grand finale. To investigate the long-term Saturn Ly{\alpha} airglow observed by different ultraviolet instruments, we cross-correlate their calibration, finding that while the official Cassini/UVIS sensitivity should be lowered by ~75%, the Voyager 1/UVS sensitivities should be enhanced by ~20% at the Ly{\alpha} channels. This comparison also allowed us to discover a permanent feature of the Saturn disk Ly{\alpha} brightness that appears at all longitudes as a brightness excess (Ly{\alpha} bulge) of ~30% (~12{\sigma}) extending over the latitude range ~5-35N compared to the regions at equator and ~60N. This feature is confirmed by three distinct instruments between 1980 & 2017 in the Saturn north hemisphere. To analyze the Ly{\alpha} observations, we use a radiation transfer (RT) model of resonant scattering of solar and interplanetary Ly{\alpha} photons, and a latitude-dependent photochemistry model of the upper atmosphere constrained by occultation and remote-sensing observations. For each latitude, we show that the Ly{\alpha} observations are sensitive to the temperature profile in the upper stratosphere and lower thermosphere, thus providing useful information in a region of the atmosphere that is difficult to probe by other means. In the Saturn Ly{\alpha} bulge region, at latitudes between ~5 to ~35{\deg}, the observed brightening and line broadening support seasonal effects, variation of the temperature vertical profile, and potential superthermal atoms that require confirmation.</description><identifier>EISSN: 2331-8422</identifier><identifier>DOI: 10.48550/arxiv.2311.14191</identifier><language>eng</language><publisher>Ithaca: Cornell University Library, arXiv.org</publisher><subject>Airglow ; Alpha rays ; Brightening ; Brightness ; Calibration ; Emission analysis ; Equatorial regions ; Line broadening ; Photochemistry ; Physics - Atmospheric and Oceanic Physics ; Physics - Earth and Planetary Astrophysics ; Physics - Instrumentation and Detectors ; Physics - Instrumentation and Methods for Astrophysics ; Remote sensing ; Saturn ; Saturn atmosphere ; Sensitivity enhancement ; Space telescopes ; Temperature profiles ; Thermosphere ; Upper atmosphere</subject><ispartof>arXiv.org, 2023-11</ispartof><rights>2023. This work is published under http://creativecommons.org/licenses/by/4.0/ (the “License”). 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Here, we report joint Hubble Space Telescope (HST) and Cassini cross-calibration observations of the Saturn Ly{\alpha} emission made two weeks before the Cassini grand finale. To investigate the long-term Saturn Ly{\alpha} airglow observed by different ultraviolet instruments, we cross-correlate their calibration, finding that while the official Cassini/UVIS sensitivity should be lowered by ~75%, the Voyager 1/UVS sensitivities should be enhanced by ~20% at the Ly{\alpha} channels. This comparison also allowed us to discover a permanent feature of the Saturn disk Ly{\alpha} brightness that appears at all longitudes as a brightness excess (Ly{\alpha} bulge) of ~30% (~12{\sigma}) extending over the latitude range ~5-35N compared to the regions at equator and ~60N. This feature is confirmed by three distinct instruments between 1980 & 2017 in the Saturn north hemisphere. To analyze the Ly{\alpha} observations, we use a radiation transfer (RT) model of resonant scattering of solar and interplanetary Ly{\alpha} photons, and a latitude-dependent photochemistry model of the upper atmosphere constrained by occultation and remote-sensing observations. For each latitude, we show that the Ly{\alpha} observations are sensitive to the temperature profile in the upper stratosphere and lower thermosphere, thus providing useful information in a region of the atmosphere that is difficult to probe by other means. In the Saturn Ly{\alpha} bulge region, at latitudes between ~5 to ~35{\deg}, the observed brightening and line broadening support seasonal effects, variation of the temperature vertical profile, and potential superthermal atoms that require confirmation.</description><subject>Airglow</subject><subject>Alpha rays</subject><subject>Brightening</subject><subject>Brightness</subject><subject>Calibration</subject><subject>Emission analysis</subject><subject>Equatorial regions</subject><subject>Line broadening</subject><subject>Photochemistry</subject><subject>Physics - Atmospheric and Oceanic Physics</subject><subject>Physics - Earth and Planetary Astrophysics</subject><subject>Physics - Instrumentation and Detectors</subject><subject>Physics - Instrumentation and Methods for Astrophysics</subject><subject>Remote sensing</subject><subject>Saturn</subject><subject>Saturn atmosphere</subject><subject>Sensitivity enhancement</subject><subject>Space telescopes</subject><subject>Temperature profiles</subject><subject>Thermosphere</subject><subject>Upper atmosphere</subject><issn>2331-8422</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>2023</creationdate><recordtype>article</recordtype><sourceid>ABUWG</sourceid><sourceid>AFKRA</sourceid><sourceid>AZQEC</sourceid><sourceid>BENPR</sourceid><sourceid>CCPQU</sourceid><sourceid>DWQXO</sourceid><sourceid>GOX</sourceid><recordid>eNotj0tLw0AUhQdBsNT-AFcOuHCVOvfOI-lSirZCwYXZh5vkTptiHk4Ssf_e2Lo6cPg4nE-IO1BLk1irnij8VN9L1ABLMLCCKzFDrSFKDOKNWPT9USmFLkZr9Uxs0gNLbqp9TUNVSMrHpqSmYNl6SUNbT93hVIZ2z42sGvlBwxiax16OXcdhIuq27w4c-FZce_rsefGfc5G-vqTrbbR737ytn3cRWYwjdIm3OZNyyKxzV3hXQOkNo4I4MRpKnTii3BdWsTYUg3GIrFRJjqwHPRf3l9mzZdaFqqZwyv5ss7PtRDxciC60XyP3Q3Zsp8vTpwyTlQGLgLH-BcgGV3k</recordid><startdate>20231123</startdate><enddate>20231123</enddate><creator>Ben-Jaffel, Lotfi</creator><creator>Moses, Julie</creator><creator>West, Robert A</creator><creator>M-K, aye</creator><creator>Bradley, Eric T</creator><creator>Clarke, John T</creator><creator>Holber, Jay B</creator><creator>Ballester, Gilda E</creator><general>Cornell University Library, arXiv.org</general><scope>8FE</scope><scope>8FG</scope><scope>ABJCF</scope><scope>ABUWG</scope><scope>AFKRA</scope><scope>AZQEC</scope><scope>BENPR</scope><scope>BGLVJ</scope><scope>CCPQU</scope><scope>DWQXO</scope><scope>HCIFZ</scope><scope>L6V</scope><scope>M7S</scope><scope>PIMPY</scope><scope>PQEST</scope><scope>PQQKQ</scope><scope>PQUKI</scope><scope>PRINS</scope><scope>PTHSS</scope><scope>GOX</scope></search><sort><creationdate>20231123</creationdate><title>The enigmatic abundance of atomic hydrogen in Saturn's upper atmosphere</title><author>Ben-Jaffel, Lotfi ; Moses, Julie ; West, Robert A ; M-K, aye ; Bradley, Eric T ; Clarke, John T ; Holber, Jay B ; Ballester, Gilda E</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-a527-268f5bea062ee3b6cf6c1df4e20178431d386aabfc50e34a714622e00da6a5f13</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>2023</creationdate><topic>Airglow</topic><topic>Alpha rays</topic><topic>Brightening</topic><topic>Brightness</topic><topic>Calibration</topic><topic>Emission analysis</topic><topic>Equatorial regions</topic><topic>Line broadening</topic><topic>Photochemistry</topic><topic>Physics - Atmospheric and Oceanic Physics</topic><topic>Physics - Earth and Planetary Astrophysics</topic><topic>Physics - Instrumentation and Detectors</topic><topic>Physics - Instrumentation and Methods for Astrophysics</topic><topic>Remote sensing</topic><topic>Saturn</topic><topic>Saturn atmosphere</topic><topic>Sensitivity enhancement</topic><topic>Space telescopes</topic><topic>Temperature profiles</topic><topic>Thermosphere</topic><topic>Upper atmosphere</topic><toplevel>online_resources</toplevel><creatorcontrib>Ben-Jaffel, Lotfi</creatorcontrib><creatorcontrib>Moses, Julie</creatorcontrib><creatorcontrib>West, Robert A</creatorcontrib><creatorcontrib>M-K, aye</creatorcontrib><creatorcontrib>Bradley, Eric T</creatorcontrib><creatorcontrib>Clarke, John T</creatorcontrib><creatorcontrib>Holber, Jay B</creatorcontrib><creatorcontrib>Ballester, Gilda E</creatorcontrib><collection>ProQuest SciTech Collection</collection><collection>ProQuest Technology Collection</collection><collection>Materials Science & Engineering Collection</collection><collection>ProQuest Central (Alumni Edition)</collection><collection>ProQuest Central UK/Ireland</collection><collection>ProQuest Central Essentials</collection><collection>ProQuest Central</collection><collection>Technology Collection</collection><collection>ProQuest One Community College</collection><collection>ProQuest Central Korea</collection><collection>SciTech Premium Collection</collection><collection>ProQuest Engineering Collection</collection><collection>Engineering Database</collection><collection>Publicly Available Content Database</collection><collection>ProQuest One Academic Eastern Edition (DO NOT USE)</collection><collection>ProQuest One Academic</collection><collection>ProQuest One Academic UKI Edition</collection><collection>ProQuest Central China</collection><collection>Engineering Collection</collection><collection>arXiv.org</collection><jtitle>arXiv.org</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>Ben-Jaffel, Lotfi</au><au>Moses, Julie</au><au>West, Robert A</au><au>M-K, aye</au><au>Bradley, Eric T</au><au>Clarke, John T</au><au>Holber, Jay B</au><au>Ballester, Gilda E</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>The enigmatic abundance of atomic hydrogen in Saturn's upper atmosphere</atitle><jtitle>arXiv.org</jtitle><date>2023-11-23</date><risdate>2023</risdate><eissn>2331-8422</eissn><abstract>A planet's Lyman-{\alpha} (Ly{\alpha}) emission is sensitive to its thermospheric structure. Here, we report joint Hubble Space Telescope (HST) and Cassini cross-calibration observations of the Saturn Ly{\alpha} emission made two weeks before the Cassini grand finale. To investigate the long-term Saturn Ly{\alpha} airglow observed by different ultraviolet instruments, we cross-correlate their calibration, finding that while the official Cassini/UVIS sensitivity should be lowered by ~75%, the Voyager 1/UVS sensitivities should be enhanced by ~20% at the Ly{\alpha} channels. This comparison also allowed us to discover a permanent feature of the Saturn disk Ly{\alpha} brightness that appears at all longitudes as a brightness excess (Ly{\alpha} bulge) of ~30% (~12{\sigma}) extending over the latitude range ~5-35N compared to the regions at equator and ~60N. This feature is confirmed by three distinct instruments between 1980 & 2017 in the Saturn north hemisphere. To analyze the Ly{\alpha} observations, we use a radiation transfer (RT) model of resonant scattering of solar and interplanetary Ly{\alpha} photons, and a latitude-dependent photochemistry model of the upper atmosphere constrained by occultation and remote-sensing observations. For each latitude, we show that the Ly{\alpha} observations are sensitive to the temperature profile in the upper stratosphere and lower thermosphere, thus providing useful information in a region of the atmosphere that is difficult to probe by other means. In the Saturn Ly{\alpha} bulge region, at latitudes between ~5 to ~35{\deg}, the observed brightening and line broadening support seasonal effects, variation of the temperature vertical profile, and potential superthermal atoms that require confirmation.</abstract><cop>Ithaca</cop><pub>Cornell University Library, arXiv.org</pub><doi>10.48550/arxiv.2311.14191</doi><oa>free_for_read</oa></addata></record> |
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subjects | Airglow Alpha rays Brightening Brightness Calibration Emission analysis Equatorial regions Line broadening Photochemistry Physics - Atmospheric and Oceanic Physics Physics - Earth and Planetary Astrophysics Physics - Instrumentation and Detectors Physics - Instrumentation and Methods for Astrophysics Remote sensing Saturn Saturn atmosphere Sensitivity enhancement Space telescopes Temperature profiles Thermosphere Upper atmosphere |
title | The enigmatic abundance of atomic hydrogen in Saturn's upper atmosphere |
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