On the Formation of Planets in the Milky Way’s Thick Disk
Exoplanet demographic surveys have revealed that close-in (≲1 au) small planets orbiting stars in the Milky Way’s thick disk are ∼50% less abundant than those orbiting stars in the Galactic thin disk. One key difference between the two stellar populations is the time at which they emerged: thick-dis...
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IOP Publishing
2025-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/ad9aa1 |
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| author | Tim Hallatt Eve J. Lee |
| author_facet | Tim Hallatt Eve J. Lee |
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| collection | DOAJ |
| description | Exoplanet demographic surveys have revealed that close-in (≲1 au) small planets orbiting stars in the Milky Way’s thick disk are ∼50% less abundant than those orbiting stars in the Galactic thin disk. One key difference between the two stellar populations is the time at which they emerged: thick-disk stars are the likely product of cosmic noon (redshift z ∼ 2), an era characterized by high star formation rate, massive and dense molecular clouds, and strong supersonic turbulence. Solving for the background radiation field in these early star-forming regions, we demonstrate that protoplanetary disks at cosmic noon experienced radiation fields up to ∼7 orders of magnitude more intense than in solar neighborhood conditions. Coupling the radiation field to a one-dimensional protoplanetary disk evolution model, we find that external UV photoevaporation destroys protoplanetary disks in just ∼0.2–0.5 Myr, limiting the timescale over which planets can assemble. Disk temperatures exceed the sublimation temperatures of common volatile species for ≳Myr timescales, predicting more spatial homogeneity in gas chemical composition. Our calculations imply that the deficit in planet occurrence around thick-disk stars should be even more pronounced for giant planets, particularly those at wide orbital separations, predicting a higher rocky-to-giant planet ratio in the Galactic thick disk versus thin disk. |
| format | Article |
| id | doaj-art-cd21cfdaa7674ab1b9837aebe79c39e4 |
| institution | Kabale University |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal |
| spelling | doaj-art-cd21cfdaa7674ab1b9837aebe79c39e42025-01-22T15:00:16ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-01979212010.3847/1538-4357/ad9aa1On the Formation of Planets in the Milky Way’s Thick DiskTim Hallatt0https://orcid.org/0000-0003-4992-8427Eve J. Lee1https://orcid.org/0000-0002-1228-9820Department of Physics and Trottier Space Institute, McGill University , Montréal, QC H3A 2T8, Canada ; thallatt@mit.edu; Institute for Research on Exoplanets (iREx) , Montréal, Québec, CanadaDepartment of Physics and Trottier Space Institute, McGill University , Montréal, QC H3A 2T8, Canada ; thallatt@mit.edu; Institute for Research on Exoplanets (iREx) , Montréal, Québec, CanadaExoplanet demographic surveys have revealed that close-in (≲1 au) small planets orbiting stars in the Milky Way’s thick disk are ∼50% less abundant than those orbiting stars in the Galactic thin disk. One key difference between the two stellar populations is the time at which they emerged: thick-disk stars are the likely product of cosmic noon (redshift z ∼ 2), an era characterized by high star formation rate, massive and dense molecular clouds, and strong supersonic turbulence. Solving for the background radiation field in these early star-forming regions, we demonstrate that protoplanetary disks at cosmic noon experienced radiation fields up to ∼7 orders of magnitude more intense than in solar neighborhood conditions. Coupling the radiation field to a one-dimensional protoplanetary disk evolution model, we find that external UV photoevaporation destroys protoplanetary disks in just ∼0.2–0.5 Myr, limiting the timescale over which planets can assemble. Disk temperatures exceed the sublimation temperatures of common volatile species for ≳Myr timescales, predicting more spatial homogeneity in gas chemical composition. Our calculations imply that the deficit in planet occurrence around thick-disk stars should be even more pronounced for giant planets, particularly those at wide orbital separations, predicting a higher rocky-to-giant planet ratio in the Galactic thick disk versus thin disk.https://doi.org/10.3847/1538-4357/ad9aa1ExoplanetsProtoplanetary disksthe Milky Way |
| spellingShingle | Tim Hallatt Eve J. Lee On the Formation of Planets in the Milky Way’s Thick Disk The Astrophysical Journal Exoplanets Protoplanetary disks the Milky Way |
| title | On the Formation of Planets in the Milky Way’s Thick Disk |
| title_full | On the Formation of Planets in the Milky Way’s Thick Disk |
| title_fullStr | On the Formation of Planets in the Milky Way’s Thick Disk |
| title_full_unstemmed | On the Formation of Planets in the Milky Way’s Thick Disk |
| title_short | On the Formation of Planets in the Milky Way’s Thick Disk |
| title_sort | on the formation of planets in the milky way s thick disk |
| topic | Exoplanets Protoplanetary disks the Milky Way |
| url | https://doi.org/10.3847/1538-4357/ad9aa1 |
| work_keys_str_mv | AT timhallatt ontheformationofplanetsinthemilkywaysthickdisk AT evejlee ontheformationofplanetsinthemilkywaysthickdisk |