Using helium 10830 Å transits to constrain planetary magnetic fields
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arXiv
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| Autori principali: | , , , , |
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| Natura: | Preprint |
| Pubblicazione: |
2023
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| _version_ | 1866929201590829056 |
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| author | Schreyer, Ethan Owen, James E. Spake, Jessica J. Bahroloom, Zahra Di Giampasquale, Simone |
| author_facet | Schreyer, Ethan Owen, James E. Spake, Jessica J. Bahroloom, Zahra Di Giampasquale, Simone |
| contents | Planetary magnetic fields can affect the predicted mass loss rate for close-in planets that experience large amounts of UV irradiation. In this work, we present a method to detect the magnetic fields of close-in exoplanets undergoing atmospheric escape using transit spectroscopy at the 10830 Angstrom line of helium. Motivated by previous work on hydrodynamic and magneto-hydrodynamic photoevaporation, we suggest that planets with magnetic fields that are too weak to control the outflow's topology lead to blue-shifted transits due to day-to-night-side flows. In contrast, strong magnetic fields prevent this day-to-night flow, as the gas is forced to follow the magnetic field's roughly dipolar topology. We post-process existing 2D photoevaporation simulations to test this concept, computing synthetic transit profiles in helium. As expected, we find that hydrodynamically dominated outflows lead to blue-shifted transits on the order of the sound speed of the gas. Strong surface magnetic fields lead to unshifted or slightly red-shifted transit profiles. High-resolution observations can distinguish between these profiles; however, eccentricity uncertainties generally mean that we cannot conclusively say velocity shifts are due to the outflow for individual planets. The majority of helium observations are blue-shifted, which could be a tentative indication that close-in planets generally have surface dipole magnetic field strengths $\lesssim 0.1$ gauss. More 3D hydrodynamic and magneto-hydrodynamic are needed to confirm this conclusion robustly. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2302_10947 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | Using helium 10830 Å transits to constrain planetary magnetic fields Schreyer, Ethan Owen, James E. Spake, Jessica J. Bahroloom, Zahra Di Giampasquale, Simone Earth and Planetary Astrophysics Solar and Stellar Astrophysics Space Physics Planetary magnetic fields can affect the predicted mass loss rate for close-in planets that experience large amounts of UV irradiation. In this work, we present a method to detect the magnetic fields of close-in exoplanets undergoing atmospheric escape using transit spectroscopy at the 10830 Angstrom line of helium. Motivated by previous work on hydrodynamic and magneto-hydrodynamic photoevaporation, we suggest that planets with magnetic fields that are too weak to control the outflow's topology lead to blue-shifted transits due to day-to-night-side flows. In contrast, strong magnetic fields prevent this day-to-night flow, as the gas is forced to follow the magnetic field's roughly dipolar topology. We post-process existing 2D photoevaporation simulations to test this concept, computing synthetic transit profiles in helium. As expected, we find that hydrodynamically dominated outflows lead to blue-shifted transits on the order of the sound speed of the gas. Strong surface magnetic fields lead to unshifted or slightly red-shifted transit profiles. High-resolution observations can distinguish between these profiles; however, eccentricity uncertainties generally mean that we cannot conclusively say velocity shifts are due to the outflow for individual planets. The majority of helium observations are blue-shifted, which could be a tentative indication that close-in planets generally have surface dipole magnetic field strengths $\lesssim 0.1$ gauss. More 3D hydrodynamic and magneto-hydrodynamic are needed to confirm this conclusion robustly. |
| title | Using helium 10830 Å transits to constrain planetary magnetic fields |
| topic | Earth and Planetary Astrophysics Solar and Stellar Astrophysics Space Physics |
| url | https://arxiv.org/abs/2302.10947 |