Thermally Driven Atmospheric Escape: Transition from Diffusion-limited to Drag-off Escape
We examine the transition from diffusion-limited to drag-off escape using a direct simulation Monte Carlo (DSMC) model developed to simulate planetary atmospheres, referred to as Harrah. A 1D spherically symmetric DSMC model is used to simulate two-component atmospheres to focus on the impact of rar...
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IOP Publishing
2025-01-01
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| Series: | The Planetary Science Journal |
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| Online Access: | https://doi.org/10.3847/PSJ/ada369 |
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| author | Jack C. Evans Shane Robert Carberry Mogan Robert E. Johnson Orenthal J. Tucker |
| author_facet | Jack C. Evans Shane Robert Carberry Mogan Robert E. Johnson Orenthal J. Tucker |
| author_sort | Jack C. Evans |
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| description | We examine the transition from diffusion-limited to drag-off escape using a direct simulation Monte Carlo (DSMC) model developed to simulate planetary atmospheres, referred to as Harrah. A 1D spherically symmetric DSMC model is used to simulate two-component atmospheres to focus on the impact of rarefaction on thermal diffusion. The results for the escape rates and thermal structure are characterized using a mass-averaged Jeans parameter, λ _avg,0 , and Knudsen number, Kn _a,0 , defined at a reference radial distance r _0 . As a test of the model, we simulated the escape of N _2 and H _2 self-consistently for conditions of Pluto’s upper atmosphere observed during the New Horizons mission. As expected, the DSMC result for H _2 escape is consistent with the diffusion-limited approximation, and H _2 escape has little effect on the background N _2 atmosphere. Then we examined the transition from diffusion-limited to drag-off escape for two-component atmospheres characterized by mass-averaged Knudsen numbers and Jeans parameters of Kn _a,0 ≈ 0.01–0.1 and λ _avg,0 ≈ 0.5–13, respectively. We found that escape transitioned from hydrodynamic escape to an enhanced Jeans-like escape at λ _avg,0 ≈ 3.0–3.6. For values of λ _avg,0 < 3.0–3.6, escape was hydrodynamic and in the blow-off regime. For values of λ _avg,0 >≈ 3.6, the DSMC results indicated that using the diffusion-limited and drag-off approximations can lead to inaccurate estimates of the escape rate. |
| format | Article |
| id | doaj-art-e5e0fcf3ca444116bc6dcd054e5e188e |
| institution | Kabale University |
| issn | 2632-3338 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Planetary Science Journal |
| spelling | doaj-art-e5e0fcf3ca444116bc6dcd054e5e188e2025-02-06T07:03:42ZengIOP PublishingThe Planetary Science Journal2632-33382025-01-01623910.3847/PSJ/ada369Thermally Driven Atmospheric Escape: Transition from Diffusion-limited to Drag-off EscapeJack C. Evans0Shane Robert Carberry Mogan1https://orcid.org/0000-0002-0261-8117Robert E. Johnson2https://orcid.org/0000-0001-7798-5918Orenthal J. Tucker3https://orcid.org/0000-0002-8235-5440Stanford University , Stanford, CA, USASpace Sciences Laboratory , University of California, Berkeley, CA, USAUniversity of Virginia , Charlottesville, VA, USANASA Goddard Space Flight Center , Greenbelt, MD, USAWe examine the transition from diffusion-limited to drag-off escape using a direct simulation Monte Carlo (DSMC) model developed to simulate planetary atmospheres, referred to as Harrah. A 1D spherically symmetric DSMC model is used to simulate two-component atmospheres to focus on the impact of rarefaction on thermal diffusion. The results for the escape rates and thermal structure are characterized using a mass-averaged Jeans parameter, λ _avg,0 , and Knudsen number, Kn _a,0 , defined at a reference radial distance r _0 . As a test of the model, we simulated the escape of N _2 and H _2 self-consistently for conditions of Pluto’s upper atmosphere observed during the New Horizons mission. As expected, the DSMC result for H _2 escape is consistent with the diffusion-limited approximation, and H _2 escape has little effect on the background N _2 atmosphere. Then we examined the transition from diffusion-limited to drag-off escape for two-component atmospheres characterized by mass-averaged Knudsen numbers and Jeans parameters of Kn _a,0 ≈ 0.01–0.1 and λ _avg,0 ≈ 0.5–13, respectively. We found that escape transitioned from hydrodynamic escape to an enhanced Jeans-like escape at λ _avg,0 ≈ 3.0–3.6. For values of λ _avg,0 < 3.0–3.6, escape was hydrodynamic and in the blow-off regime. For values of λ _avg,0 >≈ 3.6, the DSMC results indicated that using the diffusion-limited and drag-off approximations can lead to inaccurate estimates of the escape rate.https://doi.org/10.3847/PSJ/ada369Atmospheric evolutionExospherePluto |
| spellingShingle | Jack C. Evans Shane Robert Carberry Mogan Robert E. Johnson Orenthal J. Tucker Thermally Driven Atmospheric Escape: Transition from Diffusion-limited to Drag-off Escape The Planetary Science Journal Atmospheric evolution Exosphere Pluto |
| title | Thermally Driven Atmospheric Escape: Transition from Diffusion-limited to Drag-off Escape |
| title_full | Thermally Driven Atmospheric Escape: Transition from Diffusion-limited to Drag-off Escape |
| title_fullStr | Thermally Driven Atmospheric Escape: Transition from Diffusion-limited to Drag-off Escape |
| title_full_unstemmed | Thermally Driven Atmospheric Escape: Transition from Diffusion-limited to Drag-off Escape |
| title_short | Thermally Driven Atmospheric Escape: Transition from Diffusion-limited to Drag-off Escape |
| title_sort | thermally driven atmospheric escape transition from diffusion limited to drag off escape |
| topic | Atmospheric evolution Exosphere Pluto |
| url | https://doi.org/10.3847/PSJ/ada369 |
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