Spontaneous hot flow anomalies at Mars and Venus

Collinson, G.; Sibeck, D. G.; Omidi, N.; Grebowsky, J. M.; Halekas, J. S.; Mitchell, David; Espley, J. R.; Zhang, Tielong; Persson, Moa; Futaana, Yoshifumi; Jakosky, B. M.

doi:10.1002/2017ja024196

Cited by 19 publications

(25 citation statements)

References 63 publications

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“…In this study, we show convection of upstream generated magnetosonic waves into the magnetosheath similar to observations by Luhmann et al () and Shan et al (). The results presented here are consistent with recent observations of SHFAs at Venus by Collinson et al () in a companion paper. As such we expect that the Cytherean magnetosheath undergoes a continuous dynamic change in its properties during small IMF cone angles as trains of SHFAs form and dissipate at the bow shock.…”

Section: Discussionsupporting

confidence: 93%

“…In this regard, given the similarities in the size and absence of an intrinsic magnetic field at Venus and Mars, we expect the results presented here to be applicable to the latter as well. This expectation is supported in our companion paper by Collinson et al (), who show the presence of SHFAs at Venus and Mars.…”

Section: Discussionsupporting

confidence: 74%

“…The formation of HFAs at Venus was suggested by Slavin et al () and confirmed by Collinson et al (, ). Finally, in a companion paper to this one, Collinson et al () report observations of SHFAs at Venus and Mars using data from the ESA Venus Express and NASA MAVEN spacecraft. The objective of this study is to use 3‐D hybrid simulations of the Cytherean foreshock to further demonstrate that despite its smaller size, the structure and properties of this foreshock are similar to those of the terrestrial foreshock including the formation of foreshock cavitons, the FCB, and spontaneous hot flow anomalies.…”

Section: Introductionmentioning

confidence: 99%

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Structure and Properties of the Foreshock at Venus

2017

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The interaction of the solar wind with Venus is dominated by the planet's ionosphere that acts as an obstacle to the flow resulting in an induced magnetosphere and bow shock much smaller than their terrestrial counterparts. This study presents a 3‐D electromagnetic hybrid (kinetic ions and fluid electrons) simulation of the solar wind interaction with an unmagnetized obstacle to examine the structure and properties of the Cytherean foreshock during periods of near radial IMF, that is, when it lies upstream of the ionosphere. The interaction between the backstreaming ions and the solar wind results in the generation of two classes of ULF waves: (1) parallel propagating sinusoidal waves with periods ~20–30 s and (2) highly oblique fast magnetosonic waves. The joint nonlinear evolution of these waves results in the formation of structures called foreshock cavitons with dimensions comparable to the size of the planet. Foreshock cavitons are also present in the terrestrial foreshock. The excavation of plasma and magnetic field from their cores leads to lower average densities and magnetic field strengths in the foreshock. As in the case of Earth, this excavation results in the formation of a fast magnetosonic pulse/shock at the edge of the foreshock named the foreshock compressional boundary. Also similar to Earth is the formation of spontaneous hot flow anomalies (SHFAs) as foreshock cavitons approach the bow shock. The size and properties of SHFAs at Venus are comparable to those at Earth, and their existence has recently been established at Mars and Venus in a companion paper.

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Section: Discussionsupporting

confidence: 93%

Section: Discussionsupporting

confidence: 74%

Section: Introductionmentioning

confidence: 99%

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Structure and Properties of the Foreshock at Venus

2017

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“…While in this instance, the foreshock driver in question was periodic magnetosonic waves; it now seems even more plausible that pressure perturbations associated with other transient foreshock phenomena (such as hot flow anomalies, Collinson et al, , ; and spontaneous hot flow anomalies, Collinson et al, ) will also impact the ionosphere.…”

Section: Discussionmentioning

confidence: 87%

“…Recent simulations by Omidi et al () show that, despite their diminutive size with respect to the ion gyroradius, the foreshocks of unmagnetized planets are nevertheless essentially identical to that at Earth, albeit in miniature. The foreshocks of Venus and Mars exhibit the same plethora of transient phenomena as at Earth, such as whistler waves (Brain et al, ; Orlowski & Russell, ), hot flow anomalies (Collinson, Sibeck, et al, , Collinson et al, , ; Slavin et al, ), short large amplitude magnetic structures (Collinson, Wilson III, et al, ), and spontaneous hot flow anomalies (Collinson et al, ).…”

Section: Introductionmentioning

confidence: 99%

Solar Wind Induced Waves in the Skies of Mars: Ionospheric Compression, Energization, and Escape Resulting From the Impact of Ultralow Frequency Magnetosonic Waves Generated Upstream of the Martian Bow Shock

et al. 2018

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Using data from the National Aeronautics and Space Administration Mars Atmosphere and Voltatile EvolutioN and the European Space Agency Mars Express spacecraft, we show that transient phenomena in the foreshock and solar wind can directly inject energy into the ionosphere of Mars. We demonstrate that the impact of compressive ultralow frequency waves in the solar wind on the induced magnetospheres drive compressional, linearly polarized, magnetosonic ultralow frequency waves in the ionosphere, and a localized electromagnetic "ringing" at the local proton gyrofrequency. The pulsations heat and energize ionospheric plasmas. A preliminary survey of events shows that no special upstream conditions are required in the interplanetary magnetic field or solar wind. Elevated ion densities and temperatures in the solar wind near to Mars are consistent with the presence of an additional population of Martian ions, leading to ion‐ion instablities, associated wave‐particle interactions, and heating of the solar wind. The phenomenon was found to be seasonal, occurring when Mars is near perihelion. Finally, we present simultaneous multipoint observations of the phenomenon, with the Mars Express observing the waves upstream, and Mars Atmosphere and Voltatile EvolutioN observing the response in the ionosphere. When these new observations are combined with decades of previous studies, they collectively provide strong evidence for a previously undemonstrated atmospheric loss process at unmagnetized planets: ionospheric escape driven by the direct impact of transient phenomena from the foreshock and solar wind.

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A Single Deformed Bow Shock for Titan‐Saturn System

et al. 2017

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During periods of high solar wind pressure, Saturn's bow shock is pushed inside Titan's orbit exposing the moon and its ionosphere to the solar wind. The Cassini spacecraft's T96 encounter with Titan occurred during such a period and showed evidence for shocks associated with Saturn and Titan. It also revealed the presence of two foreshocks: one prior to the closest approach (foreshock 1) and one after (foreshock 2). Using electromagnetic hybrid (kinetic ions and fluid electrons) simulations and Cassini observations, we show that the origin of foreshock 1 is tied to the formation of a single deformed bow shock for the Titan‐Saturn system. We also report the observations of a structure in foreshock 1 with properties consistent with those of spontaneous hot flow anomalies formed in the simulations and previously observed at Earth, Venus, and Mars. The results of hybrid simulations also show the generation of oblique fast magnetosonic waves upstream of the outbound Titan bow shock in agreement with the observations of large‐amplitude magnetosonic pulsations in foreshock 2. We also discuss the implications of a single deformed bow shock for new particle acceleration mechanisms and also Saturn's magnetopause and magnetosphere.

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Spontaneous hot flow anomalies at Mars and Venus

Cited by 19 publications

References 63 publications

Structure and Properties of the Foreshock at Venus

Structure and Properties of the Foreshock at Venus

Solar Wind Induced Waves in the Skies of Mars: Ionospheric Compression, Energization, and Escape Resulting From the Impact of Ultralow Frequency Magnetosonic Waves Generated Upstream of the Martian Bow Shock

A Single Deformed Bow Shock for Titan‐Saturn System

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