The Radiometric Bode’s Law and Extrasolar Planets

Lazio, T. Joseph W.; Farrell, W. M.; Dietrick, Jill; Greenlees, Elizabeth; Hogan, Emily; Jones, Christopher; Hennig, L.

doi:10.1086/422449

Cited by 126 publications

(188 citation statements)

References 38 publications

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“…Properties for these three systems are shown in Table 1 with details for the full sample available in Fares et al (2013). We choose these three systems for further discussion because they are often cited as promising targets for detectable exoplanetary radio emission (Lazio et al 2004;Grießmeier et al 2007b; and have been extensively studied in the literature. In addition, these stars allow a comparison of two critical factors that affect exoplanetary radio emission.…”

Section: Stellar System Propertiesmentioning

confidence: 99%

Time-scales of close-in exoplanet radio emission variability

See

Jardine

Farès

et al. 2015

Monthly Notices of the Royal Astronomical Society

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We investigate the variability of exoplanetary radio emission using stellar magnetic maps and 3D field extrapolation techniques. We use a sample of hot Jupiter hosting stars, focusing on the HD 179949, HD 189733 and τ Boo systems. Our results indicate two time-scales over which radio emission variability may occur at magnetised hot Jupiters. The first is the synodic period of the star-planet system. The origin of variability on this time-scale is the relative motion between the planet and the interplanetary plasma that is co-rotating with the host star. The second time-scale is the length of the magnetic cycle. Variability on this time-scale is caused by evolution of the stellar field. At these systems, the magnitude of planetary radio emission is anticorrelated with the angular separation between the subplanetary point and the nearest magnetic pole. For the special case of τ Boo b, whose orbital period is tidally locked to the rotation period of its host star, variability only occurs on the time-scale of the magnetic cycle. The lack of radio variability on the synodic period at τ Boo b is not predicted by previous radio emission models, which do not account for the co-rotation of the interplanetary plasma at small distances from the star.

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Section: Stellar System Propertiesmentioning

confidence: 99%

Time-scales of close-in exoplanet radio emission variability

See

Jardine

Farès

et al. 2015

Monthly Notices of the Royal Astronomical Society

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show abstract

“…The magnetic field is a quantity that has not yet been directly observed on extrasolar planets, in spite of many attempts to detect planetary radio emission (e.g., Bastian et al 2000;Lazio et al 2004;Hallinan et al 2013;Lecavelier des Etangs et al 2013). If confirmed, the technique proposed by Vidotto et al (2010a), based on near-UV transit observations, should provide a useful tool in determining planetary magnetic field intensities for hot-Jupiter transiting systems, but may be more limited in the case of terrestrial planets orbiting dM stars (Vidotto et al 2011c).…”

Section: Introductionmentioning

confidence: 99%

Effects of M dwarf magnetic fields on potentially habitable planets

Vidotto

Jardine

Morin

et al. 2013

A&A

152

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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“…Johansson et al 2009;Vidal-Madjar et al 2003, 2004Lammer et al 2004;Chamberlain & Hunten 1987); 3) the possibility of detectable stellar-wind-powered low-frequency emissions from cEGPs similar to that from the magnetized planets in the solar system but enhanced by the stronger stellar wind (see e.g. Griessmeier et al 2007a,b;Lazio et al 2004;Farrell et al 1999;Zarka et al 2001); and 4) a range of orbital distances with quasiparallel interaction, i.e. stellar wind interaction where the interplanetary magnetic field (IMF) is approximately parallel to the stellar wind velocity in the frame of the planet.…”

Section: Introductionmentioning

confidence: 99%

Interplanetary magnetic field orientation and the magnetospheres of close-in exoplanets

Johansson

Joachim

Motschmann

2010

A&A

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The abundance of exoplanets with orbits smaller than that of Mercury most likely implies that there are exoplanets exposed to a quasiparallel stellar-wind magnetic field. Many of the generic features of stellar-wind interaction depend on the existence of a nonzero perpendicular interplanetary magnetic field component. However, for closer orbits the perpendicular component becomes smaller and smaller. The resulting quasiparallel interplanetary magnetic field may imply new types of magnetospheres and interactions not seen in the solar system. We simulate the Venus-like interaction between a supersonic stellar wind and an Earth-sized, unmagnetized terrestrial planet with ionosphere, orbiting a Sun-like star at 0.2 AU. The importance of a quasiparallel stellar-wind interaction is then studied by comparing three simulation runs with different angles between stellar wind direction and interplanetary magnetic field. The plasma simulation code is a hybrid code, representing ions as particles and electrons as a massless, charge-neutralizing adiabatic fluid. Apart from being able to observe generic features of supersonic stellar-wind interaction we observe the following changes and trends when reducing the angle between stellar wind and interplanetary magnetic field 1) that a large part of the bow shock is replaced by an unstable quasiparallel bow shock; 2) weakening magnetic draping and pile-up; 3) the creation of a second, flanking current sheet due to the need for the interplanetary magnetic field lines to connect to almost antiparallel draped field lines; 4) stellar wind reaching deeper into the dayside ionosphere; and 5) a decreasing ionospheric mass loss. The speed of the last two trends seems to accelerate at low angles.

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The Radiometric Bode’s Law and Extrasolar Planets

Cited by 126 publications

References 38 publications

Time-scales of close-in exoplanet radio emission variability

Time-scales of close-in exoplanet radio emission variability

Effects of M dwarf magnetic fields on potentially habitable planets

Interplanetary magnetic field orientation and the magnetospheres of close-in exoplanets

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