Cosmic Ray Impact on Extrasolar Earth-Like Planets in Close-in Habitable Zones

Grieβmeier, J.-M.; Stadelmann, A.; Motschmann, U.; Belisheva, N. K.; Lämmer, H.; Biernat, H. K.

doi:10.1089/ast.2005.5.587

Cited by 129 publications

(180 citation statements)

References 53 publications

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“…If we consider that r M 2 r p can still offer a reasonable protection for the planetary atmosphere, as suggested by Lammer et al (2007), then such a planet would present an auroral oval aperture of α 0 45 o and the open field line region would cover ∼30% of the planetary surface: a significantly larger area of the planet would remain exposed to, e.g., incidence of particles from the star (generated in flares, CMEs, stellar wind) and from the cosmos (galactic cosmic rays), as well as escape of planetary atmosphere through polar flows (Grießmeier et al 2005(Grießmeier et al , 2009Moore & Horwitz 2007;Khodachenko et al 2007;Lammer et al 2007). …”

Section: Conditions For Young-earth-sized Magnetospheresmentioning

confidence: 93%

“…The extent of the magnetosphere of planets orbiting in the HZ of dM stars have been investigated by other authors (e.g. Grießmeier et al 2005Grießmeier et al , 2009Khodachenko et al 2007;Lammer et al 2007;Vidotto et al 2011b,c), but, to the best of our knowledge, a detailed analysis of the particular contribution of the stellar magnetic field remains to be made. Part of this limitation is justified by the fact that it was only recently that the large-scale magnetic field of dM stars was reconstructed for the first time .…”

Section: Introductionmentioning

confidence: 99%

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Effects of M dwarf magnetic fields on potentially habitable planets

Vidotto

Jardine

Morin

et al. 2013

A&A

142

161

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We investigate the effect of the magnetic fields of M dwarf (dM) stars on potentially habitable Earth-like planets. These fields can reduce the size of planetary magnetospheres to such an extent that a significant fraction of the planet's atmosphere may be exposed to erosion by the stellar wind. We used a sample of 15 active dM stars, for which surface magnetic-field maps were reconstructed, to determine the magnetic pressure at the planet orbit and hence the largest size of its magnetosphere, which would only be decreased by considering the stellar wind. Our method provides a fast means to assess which planets are most affected by the stellar magnetic field, which can be used as a first study to be followed by more sophisticated models. We show that hypothetical Earth-like planets with similar terrestrial magnetisation (∼1 G) orbiting at the inner (outer) edge of the habitable zone of these stars would present magnetospheres that extend at most up to 6 (11.7) planetary radii. To be able to sustain an Earth-sized magnetosphere, with the exception of only a few cases, the terrestrial planet would either (1) need to orbit significantly farther out than the traditional limits of the habitable zone; or else, (2) if it were orbiting within the habitable zone, it would require at least a magnetic field ranging from a few G to up to a few thousand G. By assuming a magnetospheric size that is more appropriate for the young-Earth (3.4 Gyr ago), the required planetary magnetic fields are one order of magnitude weaker. However, in this case, the polar-cap area of the planet, which is unprotected from transport of particles to/from interplanetary space, is twice as large. At present, we do not know how small the smallest area of the planetary surface is that could be exposed and would still not affect the potential for formation and development of life in a planet. As the star becomes older and, therefore, its rotation rate and magnetic field reduce, the interplanetary magnetic pressure decreases and the magnetosphere of planets probably expands. Using an empirically derived rotation-activity/magnetism relation, we provide an analytical expression for estimating the shortest stellar rotation period for which an Earth-analogue in the habitable zone could sustain an Earth-sized magnetosphere. We find that the required rotation rate of the early-and mid-dM stars (with periods 37-202 days) is slower than the solar one, and even slower for the late-dM stars ( 63-263 days). Planets orbiting in the habitable zone of dM stars that rotate faster than this have smaller magnetospheric sizes than that of the Earth magnetosphere. Because many late-dM stars are fast rotators, conditions for terrestrial planets to harbour Earth-sized magnetospheres are more easily achieved for planets orbiting slowly rotating early-and mid-dM stars.

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Section: Conditions For Young-earth-sized Magnetospheresmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Effects of M dwarf magnetic fields on potentially habitable planets

Vidotto

Jardine

Morin

et al. 2013

A&A

142

161

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“…As a consequence, the dynamo-generated magnetic moment will be comparatively small, and the ram pressure of the solar/stellar wind will compresses the magnetosphere sufficiently to expose the upper atmosphere to the solar/stellar wind; this effect is particularly strong if the upper atmosphere is heated and expanded by strong EUV/X-ray flux from a magnetically active central star. Magnetic protection of the atmosphere is thus strongly reduced (Grießmeier et al 2005;Lammer et al 2007). At the same time, the cosmic ray flux above the planetary atmosphere will be enhanced given the weaker and smaller magnetosphere (Grießmeier et al 2005).…”

Section: High-energy Radiation and The Stellar Environmentmentioning

confidence: 99%

“…Magnetic protection of the atmosphere is thus strongly reduced (Grießmeier et al 2005;Lammer et al 2007). At the same time, the cosmic ray flux above the planetary atmosphere will be enhanced given the weaker and smaller magnetosphere (Grießmeier et al 2005).…”

Section: High-energy Radiation and The Stellar Environmentmentioning

confidence: 99%

Magnetic activity, high-energy radiation and variability: from young solar analogs to low-mass objects

Güdel

2009

Proc. IAU

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Abstract. Magnetic activity on cool stars expresses itself in a bewildering variety of radiative and particle output originating from magnetic regions between the photosphere and the corona. Given its origin in evolving magnetic fields, most of this output is variable in time. Radiation in the ultraviolet, the extreme ultraviolet, and the X-ray ranges are important for heating and ionizing upper planetary atmospheres and thus driving atmospheric evaporation. Additionally, stellar winds interact with the upper atmospheres and may lead to further erosion. The stellar high-energy output is therefore a prime factor in determining habitability of planets. We summarize our knowledge of magnetic activity in young solar analogs and lower-mass stars and show how the stellar output changes on evolutionary timescales.

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“…For planets with a strong magnetic field, most galactic cosmic-ray particles are deflected, whereas for weakly magnetized planets, the majority of the particles can reach the planetary atmosphere. In previous work (Grießmeier et al 2005(Grießmeier et al , 2009, the flux of galactic cosmic rays to the atmosphere of extrasolar planets has been evaluated on the basis of a simple estimate for the planetary magnetic moment. However, such quantitative estimates of magnetic fields can be over-simplistic.…”

Section: Introductionmentioning

confidence: 99%

Galactic cosmic rays on extrasolar Earth-like planets

Grießmeier

Vakili

Stadelmann

et al. 2016

A&A

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Context. Theoretical arguments indicate that close-in terrestial exoplanets may have weak magnetic fields. As described in the companion article (Paper I), a weak magnetic field results in a high flux of galactic cosmic rays to the top of the planetary atmosphere. Aims. We investigate effects that may result from a high flux of galactic cosmic rays both throughout the atmosphere and at the planetary surface. Methods. Using an air shower approach, we calculate how the atmospheric chemistry and temperature change under the influence of galactic cosmic rays for Earth-like (N 2 -O 2 dominated) atmospheres. We evaluate the production and destruction rate of atmospheric biosignature molecules. We derive planetary emission and transmission spectra to study the influence of galactic cosmic rays on biosignature detectability. We then calculate the resulting surface UV flux, the surface particle flux, and the associated equivalent biological dose rates. Results. We find that up to 20% of stratospheric ozone is destroyed by cosmic-ray protons. The effect on the planetary spectra, however, is negligible. The reduction of the planetary ozone layer leads to an increase in the weighted surface UV flux by two orders of magnitude under stellar UV flare conditions. The resulting biological effective dose rate is, however, too low to strongly affect surface life. We also examine the surface particle flux: For a planet with a terrestrial atmosphere (with a surface pressure of 1033 hPa), a reduction of the magnetic shielding efficiency can increase the biological radiation dose rate by a factor of two, which is non-critical for biological systems. For a planet with a weaker atmosphere (with a surface pressure of 97.8 hPa), the planetary magnetic field has a much stronger influence on the biological radiation dose, changing it by up to two orders of magnitude. Conclusions. For a planet with an Earth-like atmospheric pressure, weak or absent magnetospheric shielding against galactic cosmic rays has little effect on the planet. It has a modest effect on atmospheric ozone, a weak effect on the atmospheric spectra, and a noncritical effect on biological dose rates. For planets with a thin atmosphere, however, magnetospheric shielding controls the surface radiation dose and can prevent it from increasing to several hundred times the background level.

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Cosmic Ray Impact on Extrasolar Earth-Like Planets in Close-in Habitable Zones

Cited by 129 publications

References 53 publications

Effects of M dwarf magnetic fields on potentially habitable planets

Effects of M dwarf magnetic fields on potentially habitable planets

Magnetic activity, high-energy radiation and variability: from young solar analogs to low-mass objects

Galactic cosmic rays on extrasolar Earth-like planets

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