Planetary magnetic field control of ion escape from weakly magnetized planets

Egan, Hilary; Järvinen, R.; Ma, Yingjuan; Brain, David

doi:10.1093/mnras/stz1819

Cited by 67 publications

(58 citation statements)

References 94 publications

(95 reference statements)

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“…In a recent hybrid study, Egan et al. (2019) investigated how the solar wind interacts with a Mars‐sized planet, its ionosphere and the resulting ion escape. This planet has been assigned a weak dipole field.…”

Section: Simulation Resultsmentioning

confidence: 99%

Influence of Mercury's Exosphere on the Structure of the Magnetosphere

et al. 2020

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Mercury is embedded in a tenuous and highly anisotropic sodium exosphere, generated mainly by plasma‐surface interactions. The absolute values of the sodium ion density are still under debate. Observations by MESSENGER's Fast Imaging Plasma Spectrometer (FIPS) instrument suggest the density of exospheric ions to be several orders of magnitude lower than the upstream solar wind density, indicating that the sodium exosphere has no substantial influence on the magnetospheric current systems. However, MESSENGER magnetic field observations of field line resonances revealed sodium ion densities comparable to the upstream solar wind density. To investigate how a dense exosphere would affect the current systems within Mercury's magnetosphere, we apply an established hybrid (kinetic ions, fluid electrons) model and conduct multiple model runs with gradually increasing exospheric density, ranging from no sodium ions at all to comet‐like configurations. We demonstrate how a sufficiently dense exosphere leads to self‐shielding of the sodium ion population from the ambient electric field and a significant inflation and symmetrization of Mercury's magnetosphere, which is decreasingly affected by the dipole offset. Once the sodium ion density is sufficiently high, Region 2 field‐aligned currents emerge close to the planet. The modeled Region 2 currents are located below the orbit of MESSENGER, thereby providing a possible explanation for the absence of these currents in observations. The sodium exosphere also closes a significant fraction of the Region 1 currents through Pedersen and Hall currents before the “guiding” magnetic field lines even reach the planetary surface. The modeled sodium ion and solar wind densities agree well with observations.

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Section: Simulation Resultsmentioning

confidence: 99%

Influence of Mercury's Exosphere on the Structure of the Magnetosphere

et al. 2020

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“…MHD simulations of present Mars with a weak dipole field also indicated that the existence of a weak intrinsic global dipole magnetic field increases ion loss . Some hybrid simulation studies reported the same effects of a weak intrinsic magnetic field on ion loss, while they also showed that the existence of a strong intrinsic magnetic field reduces ion loss (Egan et al, 2019;Kallio & Barabash, 2012). Investigating more precise contributions of an intrinsic magnetic field to ion loss is important for understanding the evolution of the atmosphere and the climate of Mars.…”

Section: Introductionmentioning

confidence: 96%

Effects of an Intrinsic Magnetic Field on Ion Loss From Ancient Mars Based on Multispecies MHD Simulations

et al. 2020

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Ion loss to space has played an important role in atmospheric escape and climate change on Mars because of intense solar activity during a younger, more active phase of the Sun. Although the existence of an intrinsic magnetic field on ancient Mars is also a key factor in ion loss, its effect remains unclear. Based on multispecies magnetohydrodynamics (MHD) simulations, we investigated processes and rates of ion loss from Mars under extreme solar conditions and the existence of a dipole field with different strengths. The effects of a dipole field on ion loss depend on whether the dipolar magnetic pressure is strong enough to sustain the solar wind dynamic pressure. When the dipole field is existent but weak, it facilitates the cusp outflow and increases the loss rates of molecular ions (O2+ and CO2+) by a factor of 6 through the high‐latitude magnetotail. When the dipole field is strong enough, the loss rates of molecular ions are decreased by 2 orders of magnitude, and peaks of the escape flux are located near the equatorial plane due to the magnetic reconnection in the northern‐dusk or southern‐dawn lobe regions. The pickup process on the extended oxygen corona created by the strong EUV flux contributes to the total O+ loss. Therefore, the effects of the dipole field are less pronounced for O+. Under more moderate solar EUV conditions, the effects on O+ loss can be stronger and thus contribute to climate change.

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“…This is, for example, what is believed to have happened to Mars, which does not have an intrinsic magnetic field, therefore lacking a protective 'umbrella' against the solar wind. Recently, there has been a debate in the literature whether this is indeed the case, with some authors arguing that magnetic fields do not affect atmospheric escape, with Mars and Earth being counter examples of unmagnetised and magnetised planets, respectively, with similar outflow rates (Strangeway et al 2010, see also Blackman & Tarduno 2018;Egan et al 2019). Although escape in solar system planets can help us understand exoplanet evaporation (or atmospheric survival), the different, and often very extreme, architectures of exoplanetary systems compared to the solar system does not necessary guarantee that the same evaporation mechanisms taking place in the solar system would operate (or be as strong) in the exoplanets knows to date.…”

Section: Atmospheric Creation or Evaporationmentioning

confidence: 99%

Different types of star-planet interactions

Vidotto

2019

Proc. IAU

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Stars and their exoplanets evolve together. Depending on the physical characteristics of these systems, such as age, orbital distance and activity of the host stars, certain types of star-exoplanet interactions can dominate during given phases of the evolution. Identifying observable signatures of such interactions can provide additional avenues for characterising exoplanetary systems. Here, I review some recent works on star-planet interactions and discuss their observability at different wavelengths across the electromagnetic spectrum.

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Planetary magnetic field control of ion escape from weakly magnetized planets

Cited by 67 publications

References 94 publications

Influence of Mercury's Exosphere on the Structure of the Magnetosphere

Influence of Mercury's Exosphere on the Structure of the Magnetosphere

Effects of an Intrinsic Magnetic Field on Ion Loss From Ancient Mars Based on Multispecies MHD Simulations

Different types of star-planet interactions

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