The infant bow shock: a new frontier at a weak activity comet

Gunell, H.; Goetz, Charlotte; Wedlund, Cyril Simon; Lindkvist, Jesper; Hamrin, Maria; Nilsson, Hans; LLera, Kristie; Eriksson, Anders; Holmström, Mats

doi:10.1051/0004-6361/201834225

Cited by 45 publications

(94 citation statements)

References 24 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Water group pick-up ions were observed as they were being accelerated by the solar wind electric field, and the solar wind protons were seen to be deflected by about 20 • , but they were otherwise generally unaffected by the presence of the comet. Closer to the Sun, Rosetta observed the infant bow shock, that is to say a bow shock during its formation (Gunell et al 2018). Then, when comet 67P was less than 1.8 AU from the Sun, no solar wind ions could be detected at all at the spacecraft position (Nilsson et al 2017).…”

Section: Introductionmentioning

confidence: 99%

Polarisation of a small-scale cometary plasma environment

Gunell

Lindkvist

Goetz

et al. 2019

A&A

Self Cite

View full text Add to dashboard Cite

Context. The plasma near the nucleus of a comet is subjected to an electric field to which a few different sources contribute: the convective electric field of the solar wind, the ambipolar electric field due to higher electron than ion speeds, and a polarisation field arising from the vastly different ion and electron trajectories. Aims. Our aim is to show how the ambipolar and polarisation electric fields arise and develop under the influence of space charge effects, and in doing so we paint a qualitative picture of the electric fields in the inner coma of a comet. Methods. We use an electrostatic particle-in-cell model to simulate a scaled-down comet, representing comet 67P/Churyumov-Gerasimenko with parameters corresponding to a 3.0 AU heliocentric distance. Results. We find that an ambipolar electric field develops early in the simulation and that this is soon followed by the emergence of a polarisation electric field, manifesting itself as an anti-sunward component prevalent in the region surrounding the centre of the comet. As plasma is removed from the inner coma in the direction of the convectional electric field of the solar wind, a density maximum develops on the opposite side of the centre of the comet. Conclusions. The ambipolar and polarisation electric fields both have a significant influence on the motion of cometary ions. This demonstrates the importance of space charge effects in comet plasma physics.

show abstract

Section: Introductionmentioning

confidence: 99%

Polarisation of a small-scale cometary plasma environment

Gunell

Lindkvist

Goetz

et al. 2019

A&A

Self Cite

View full text Add to dashboard Cite

show abstract

“…The bow shock, a permanent boundary where mass loading of the solar wind flow causes it to transition from supersonic to subsonic, was observed by several spacecraft flybys (e.g., Galeev et al 1986). Rosetta observed the bow shock of 67P/Churyumov-Gerasimenko (67P) shortly after it first formed (Gunell et al 2018), which is a stage of development not previously observed by any mission. However, only the Rosetta mission (Goetz et al 2016(Goetz et al , 2017Nemeth et al 2016) and the Giotto flyby of Halley (Neubauer et al 1986) approached close enough to the nucleus to detect the boundary of the diamagnetic cavity, a magnetic-field free region surrounding the comet nucleus.…”

Section: Introductionmentioning

confidence: 86%

Influence of collisions on ion dynamics in the inner comae of four comets

Mandt

Eriksson

Beth

et al. 2019

A&A

View full text Add to dashboard Cite

Context. Collisions between cometary neutrals in the inner coma of a comet and cometary ions that have been picked up into the solar wind flow and return to the coma lead to the formation of a broad inner boundary known as a collisionopause. This boundary is produced by a combination of charge transfer and chemical reactions, both of which are important at the location of the collisionopause boundary. Four spacecraft measured ion densities and velocities in the inner region of comets, exploring the part of the coma where an ion-neutral collisionopause boundary is expected to form. Aims. The aims are to determine the dominant physics behind the formation of the ion-neutral collisionopause and to evaluate where this boundary has been observed by spacecraft. Methods. We evaluated observations from three spacecraft at four different comets to determine if a collisionopause boundary was observed based on the reported ion velocities. We compared the measured location of the ion-neutral collisionopause with measurements of the collision cross sections to evaluate whether chemistry or charge exchange are more important at the location where the collisionopause is observed. Results. Based on measurements of the cross sections for charge transfer and for chemical reactions, the boundary observed by Rosetta appears to be the location where chemistry becomes the more probable result of a collision between H2O and H2O+ than charge exchange. Comparisons with ion observations made by Deep Space 1 at 19P/Borrelly and Giotto at 1P/Halley and 26P/Grigg-Skjellerup show that similar boundaries were observed at 19P/Borrelly and 1P/Halley. The ion composition measurements made by Giotto at Halley confirm that chemistry becomes more important inside of this boundary and that electron-ion dissociative recombination is a driver for the reported ion pileup boundary.

show abstract

“…Article number, page 9 of 17 A&A proofs: manuscript no. ICA_solar_wind_charge_exchange_PaperII At this level of cometary activity for 67P, no full-fledged bow shock structure is expected to have formed yet, although indications of a bow shock in the process of formation have been reported in Gunell et al (2018) already at around 2.5 AU and within 100 km from the nucleus. These authors found that He 2+ ions move further downstream before being affected by the heating due to the presence of the shock-like structure.…”

Section: Variation With Solar Wind Speedmentioning

confidence: 92%

Solar wind charge exchange in cometary atmospheres

Wedlund

Béhar

Kallio

et al. 2019

A&A

Self Cite

View full text Add to dashboard Cite

Context. Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet because they mass-load the solar wind through an effective conversion of fast, light solar wind ions into slow, heavy cometary ions. The ESA/Rosetta mission to comet 67P/Churyumov-Gerasimenko (67P) provided a unique opportunity to study charge-changing processes in situ. Aims. To understand the role of charge-changing reactions in the evolution of the solar wind plasma and to interpret the complex in situ measurements made by Rosetta, numerical or analytical models are necessary.Methods. An extended analytical formalism describing solar wind charge-changing processes at comets along solar wind streamlines is presented. It is based on a thorough book-keeping of available charge-changing cross sections of hydrogen and helium particles in a water gas. Results. After presenting a general 1D solution of charge exchange at comets, we study the theoretical dependence of charge-state distributions of (He 2+ , He + , He 0 ) and (H + , H 0 , H − ) on solar wind parameters at comet 67P. We show that double charge exchange for the He 2+ −H 2 O system plays an important role below a solar wind bulk speed of 200 km s −1 , resulting in the production of He energetic neutral atoms, whereas stripping reactions can in general be neglected. Retrievals of outgassing rates and solar wind upstream fluxes from local Rosetta measurements deep in the coma are discussed. Solar wind ion temperature effects at 400 km s −1 solar wind speed are well contained during the Rosetta mission. Conclusions. As the comet approaches perihelion, the model predicts a sharp decrease of solar wind ion fluxes by almost one order of magnitude at the location of Rosetta, forming in effect a solar wind ion cavity. This study is the second part of a series of three on solar wind charge-exchange and ionization processes at comets, with a specific application to comet 67P and the Rosetta mission.

show abstract

The infant bow shock: a new frontier at a weak activity comet

Cited by 45 publications

References 24 publications

Polarisation of a small-scale cometary plasma environment

Polarisation of a small-scale cometary plasma environment

Influence of collisions on ion dynamics in the inner comae of four comets

Solar wind charge exchange in cometary atmospheres

Contact Info

Product

Resources

About