Planetary Magnetospheres

Bagenal, F.

doi:10.1007/978-94-007-5606-9_6

Cited by 35 publications

(25 citation statements)

References 178 publications

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“…R M is given here in planetary radii, B p is the surface planetary magnetic field at the equator, which we assume to be the dipolar field only. The factor of 1.4 accounts for currents that develop near the magnetopause boundary and produce their own magnetic fields (Cravens 1997;Bagenal 2013). Equation (23) shows a dependence on stellar wind strength, which could have important ramifications for the development of life, as the solar wind is expected to have varied in the past on long timescales, as we have shown in Section 3.…”

Section: Evolution Of the Local Properties Of The Windmentioning

confidence: 99%

“…In the solar system, the Earth has the largest magnetosphere of the terrestrial planets. This magnetosphere shields the Earth from the harmful solar wind and also dynamically changes with the evolving solar wind (Cravens 1997;Bagenal 2013) and planetary dynamo. If the wind of the Sun changes on evolutionary timescales, then it is expected that the Earth's magnetosphere will evolve on similar timescales.…”

Section: Planetary Environmentsmentioning

confidence: 99%

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The solar wind in time: a change in the behaviour of older winds?

Fionnagáin

Vidotto

2018

Monthly Notices of the Royal Astronomical Society

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In the present paper, we model the wind of solar analogues at different ages to investigate the evolution of the solar wind. Recently, it has been suggested that winds of solar type stars might undergo a change in properties at old ages, whereby stars older than the Sun would be less efficient in carrying away angular momentum than what was traditionally believed. Adding to this, recent observations suggest that old solar-type stars show a break in coronal properties, with a steeper decay in X-ray luminosities and temperatures at older ages. We use these X-ray observations to constrain the thermal acceleration of winds of solar analogues. Our sample is based on the stars from the 'Sun in time' project with ages between 120-7000 Myr. The break in X-ray properties leads to a break in wind mass-loss rates ( M) at roughly 2 Gyr, with M (t < 2 Gyr) ∝ t −0.74 and M (t > 2 Gyr) ∝ t −3.9 . This steep decay in M at older ages could be the reason why older stars are less efficient at carrying away angular momentum, which would explain the anomalously rapid rotation observed in older stars. We also show that none of the stars in our sample would have winds dense enough to produce thermal emission above 1-2 GHz, explaining why their radio emissions have not yet been detected. Combining our models with dynamo evolution models for the magnetic field of the Earth we find that, at early ages (≈100 Myr) our Earth had a magnetosphere that was 3 or more times smaller than its current size.1 Ro represents Rossby number, which is the ratio between stellar rotation and convective turnover time. Ro = P rot /τ conv

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Section: Evolution Of the Local Properties Of The Windmentioning

confidence: 99%

Section: Planetary Environmentsmentioning

confidence: 99%

The solar wind in time: a change in the behaviour of older winds?

Fionnagáin

Vidotto

2018

Monthly Notices of the Royal Astronomical Society

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“…Although every plasma process is conceivably a multi-scale process, we, by practical necessity, only address the physics processes we consider most relevant to the multi-scale evolution of the solar wind. The most prominent processes not covered in this review include detailed discussions of reconnection (Pontin, 2011;Gosling, 2012;Paschmann et al, 2013), shock waves Chashei and Shishov, 1997;Lepping, 2000;Rice and Zank, 2003), the physics of the outer heliosphere (pick-up ions, energetic neutral atoms, etc., Zank et al, 1995;Zank, 1999;Richardson et al, 2004;McComas et al, 2012;Zank et al, 2018), interplanetary dust (Krüger et al, 2007;Mann et al, 2010), interactions with planetary bodies (Grard et al, 1991;Kivelson and Bagenal, 2007;Gardini et al, 2011;Bagenal, 2013), eruptive events such as coronal mass ejections (Zurbuchen and Richardson, 2006;Howard and Tappin, 2009;Webb and Howard, 2012), solar energetic particles (Ryan et al, 2000;Mikić and Lee, 2006;Klein and Dalla, 2017), and (anomalous) cosmic rays (Heber et al, 2006;Potgieter, 2008;Giacalone et al, 2012;Potgieter, 2013). We also limit our discussion of minor-ion physics.…”

Section: Introductionmentioning

confidence: 99%

The multi-scale nature of the solar wind

Verscharen¹,

Klein²,

Maruca³

2019

Living Rev Sol Phys

336

285

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The solar wind is a magnetized plasma and as such exhibits collective plasma behavior associated with its characteristic spatial and temporal scales. The characteristic length scales include the size of the heliosphere, the collisional mean free paths of all species, their inertial lengths, their gyration radii, and their Debye lengths. The characteristic timescales include the expansion time, the collision times, and the periods associated with gyration, waves, and oscillations. We review the past and present research into the multi-scale nature of the solar wind based on in-situ spacecraft measurements and plasma theory. We emphasize that couplings of processes across scales are important for the global dynamics and thermodynamics of the solar wind. We describe methods to measure in-situ properties of particles and fields. We then discuss the role of expansion effects, non-equilibrium distribution functions, collisions,

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“…These magnetic fields are largely dipolar, and create cavities, preventing the solar wind from reaching the surface directly (e.g. Bagenal 2013). Recently, there have been discussions on whether smaller or larger magnetospheres can protect the atmospheres of planets (Strangeway et al 2010;Brain et al 2013;Vidotto 2013;Tarduno et al 2014;Blackman & Tarduno 2018).…”

Section: Introductionmentioning

confidence: 99%

The evolution of Earth’s magnetosphere during the solar main sequence

Carolan

Vidotto

Loesch³

et al. 2019

Monthly Notices of the Royal Astronomical Society

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As a star spins-down during the main sequence, its wind properties are affected. In this work, we investigate how the Earth's magnetosphere has responded to the change in the solar wind. Earth's magnetosphere is simulated using 3D magnetohydrodynamic models that incorporate the evolving local properties of the solar wind. The solar wind, on the other hand, is modelled in 1.5D for a range of rotation rates Ω from 50 to 0.8 times the present-day solar rotation (Ω ). Our solar wind model uses empirical values for magnetic field strengths, base temperature and density, which are derived from observations of solar-like stars. We find that for rotation rates 10Ω , Earth's magnetosphere was substantially smaller than it is today, exhibiting a strong bow shock. As the sun spins down, the magnetopause standoff distance varies with Ω −0.27 for higher rotation rates (early ages, ≥ 1.4Ω ), and with Ω −2.04 for lower rotation rates (older ages, < 1.4Ω ). This break is a result of the empirical properties adopted for the solar wind evolution. We also see a linear relationship between magnetopause distance and the thickness of the shock on the subsolar line for the majority of the evolution (≤ 10Ω ). It is possible that a young fast rotating Sun would have had rotation rates as high as 30 to 50Ω . In these speculative scenarios, at 30Ω , a weak shock would have been formed, but for 50Ω , we find that no bow shock could be present around Earth's magnetosphere. This implies that with the Sun continuing to spin down, a strong shock would have developed around our planet, and remained for most of the duration of the solar main sequence.

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Planetary Magnetospheres

Cited by 35 publications

References 178 publications

The solar wind in time: a change in the behaviour of older winds?

The solar wind in time: a change in the behaviour of older winds?

The multi-scale nature of the solar wind

The evolution of Earth’s magnetosphere during the solar main sequence

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