Galactic cosmic rays on extrasolar Earth-like planets I. Cosmic ray flux
| Autor: | Grießmeier, J. -M., Tabataba-Vakili, F., Stadelmann, A., Grenfell, J. L., Atri, D. |
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| Rok vydání: | 2015 |
| Předmět: | |
| Zdroj: | A&A 581, A44 (2015) |
| Druh dokumentu: | Working Paper |
| DOI: | 10.1051/0004-6361/201425451 |
| Popis: | (abridged abstract) Theoretical arguments indicate that close-in terrestial exoplanets may have weak magnetic fields, especially in the case of planets more massive than Earth (super-Earths). Planetary magnetic fields, however, constitute one of the shielding layers that protect the planet against cosmic-ray particles. In particular, a weak magnetic field results in a high flux of Galactic cosmic rays that extends to the top of the planetary atmosphere. We wish to quantify the flux of Galactic cosmic rays to an exoplanetary atmosphere as a function of the particle energy and of the planetary magnetic moment. We numerically analyzed the propagation of Galactic cosmic-ray particles through planetary magnetospheres. We evaluated the efficiency of magnetospheric shielding as a function of the particle energy (in the range 16 MeV $\le$ E $\le$ 524 GeV) and as a function of the planetary magnetic field strength (in the range 0 ${M}_\oplus$ $\le$ {M} $\le$ 10 ${M}_\oplus$). Combined with the flux outside the planetary magnetosphere, this gives the cosmic-ray energy spectrum at the top of the planetary atmosphere as a function of the planetary magnetic moment. We find that the particle flux to the planetary atmosphere can be increased by more than three orders of magnitude in the absence of a protecting magnetic field. For a weakly magnetized planet (${M}=0.05\,{M}_{\oplus}$), only particles with energies below 512 MeV are at least partially shielded. For a planet with a magnetic moment similar to Earth, this limit increases to 32 GeV, whereas for a strongly magnetized planet ($M=10.0\,{M}_{\oplus}$), partial shielding extends up to 200 GeV. We find that magnetic shielding strongly controls the number of cosmic-ray particles reaching the planetary atmosphere. The implications of this increased particle flux are discussed in a companion article. Comment: 10 pages, 9 figures; accepted in A&A |
| Databáze: | arXiv |
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