Influences on the radius of the auroral oval

Milan, S. E.; Hutchinson, James A.; Boakes, Peter; Hubert, Benoît

doi:10.5194/angeo-27-2913-2009

Cited by 91 publications

(208 citation statements)

References 43 publications

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“…The category 2 SYM-H fluctuates at lower magnitudes than that for category 1 and the control line, gradually increasing in magnitude over the entire period of study. The negative enhancement of the SYM-H index for substorm events with larger values of F pc (category 1) is consistent with results of previous superposed studies [Milan et al, , 2009a[Milan et al, , 2009bHuang et al, 2009].…”

Section: Geomagnetic Activitysupporting

confidence: 81%

A superposed epoch investigation of the relation between magnetospheric solar wind driving and substorm dynamics with geosynchronous particle injection signatures

et al. 2011

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Section: Geomagnetic Activitysupporting

confidence: 81%

A superposed epoch investigation of the relation between magnetospheric solar wind driving and substorm dynamics with geosynchronous particle injection signatures

et al. 2011

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“…We note that a stronger external pressure not only makes r M smaller, but also exposes a larger area of the polar cap of the planet. For the Earth, the aperture of the auroral oval is α 0 17−20 • (Milan et al 2009), which implies that the open-field-line region covers only ∼5−6% of the surface. Figure 2b shows the aperture of the auroral oval that the hypothetical planets would present if they were orbiting the inner (circles) and outer (squares) edges of the HZ.…”

Section: Active M-dwarf Planet Hostsmentioning

confidence: 99%

“…Although there is a number of known old, slowly rotating latedM stars with rotation periods of up to 100 days (Irwin et al 2011;Goulding et al 2012;McQuillan et al 2013), the fraction of inactive dM stars is considerably lower for late-dM stars (West et al 2008). Furthermore, because their rotational braking time scales are probably longer (∼6−10 Gyr, West et al 2008;Irwin et al 2011) than the lifetime of the dipole-dominated planetary fields ( 3 Gyr, Zuluaga & Cuartas 2012), it may be more difficult for an old ( 6 Gyr) Earth-like planet to generate a significant dipolar magnetic field.…”

Section: Weakly-active M-dwarf Planet Hostsmentioning

confidence: 99%

Effects of M dwarf magnetic fields on potentially habitable planets

Vidotto

Jardine

Morin

et al. 2013

A&A

145

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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“…To estimate the total outflow, we assume a total polar cap area of 3-6×10 17 cm 2 (low to high geomagnetic activity), (Li et al 2012, Milan et al 2009, 2012. The mapped outward ion flux is about 2 to about 4×10 8 cm −2 s −1 (low to high solar EUV, figure 4).…”

Section: Low-energy Ions and A Better Map Of Near-earth Spacementioning

confidence: 99%

Previously hidden low-energy ions: a better map of near-Earth space and the terrestrial mass balance

André

2015

Phys. Scr.

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This is a review of the mass balance of planet Earth, intended also for scientists not usually working with space physics or geophysics. The discussion includes both outflow of ions and neutrals from the ionosphere and upper atmosphere, and the inflow of meteoroids and larger objects. The focus is on ions with energies less than tens of eV originating from the ionosphere. Positive low-energy ions are complicated to detect onboard sunlit spacecraft at higher altitudes, which often become positively charged to several tens of volts. We have invented a technique to observe low-energy ions based on the detection of the wake behind a charged spacecraft in a supersonic ion flow. We find that low-energy ions usually dominate the ion density and the outward flux in large volumes in the magnetosphere. The global outflow is of the order of 10 26 ions s -1 . This is a significant fraction of the total number outflow of particles from Earth, and changes plasma processes in near-Earth space. We compare order of magnitude estimates of the mass outflow and inflow for planet Earth and find that they are similar, at around 1 kg s −1 (30 000 ton yr −1 ). We briefly discuss atmospheric and ionospheric outflow from other planets and the connection to evolution of extraterrestrial life.

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Influences on the radius of the auroral oval

Cited by 91 publications

References 43 publications

A superposed epoch investigation of the relation between magnetospheric solar wind driving and substorm dynamics with geosynchronous particle injection signatures

A superposed epoch investigation of the relation between magnetospheric solar wind driving and substorm dynamics with geosynchronous particle injection signatures

Effects of M dwarf magnetic fields on potentially habitable planets

Previously hidden low-energy ions: a better map of near-Earth space and the terrestrial mass balance

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