Hybrid modelling of cometary plasma environments

Wedlund, Cyril Simon; Alho, Markku; Gronoff, Guillaume; Kallio, Esa; Gunell, H.; Nilsson, Hans; Lindkvist, Jesper; Béhar, Etienne; Wieser, Gabriella Stenberg; Miloch, W. J.

doi:10.1051/0004-6361/201730514

Cited by 44 publications

(43 citation statements)

References 112 publications

(160 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Lengths are in units of 10 5 km solar wind Mach number diminishes and/or gas production rate increases. Recent models show that the dimensions of the bowshock increase with greater photoionization, chargeexchange, and electron impact ionization (Simon Wedlund et al 2017). Consequently, the dimensions of the magnetosheath region of shocked solar wind plasma behind the dayside bow shock should also increase as comets move sunward and sublimation increases (Flammer 1991).…”

Section: Cometsmentioning

confidence: 99%

Imaging Plasma Density Structures in the Soft X-Rays Generated by Solar Wind Charge Exchange with Neutrals

et al. 2018

View full text Add to dashboard Cite

Both heliophysics and planetary physics seek to understand the complex nature of the solar wind's interaction with solar system obstacles like Earth's magnetosphere, the ionospheres of Venus and Mars, and comets. Studies with this objective are frequently conducted with the help of single or multipoint in situ electromagnetic field and particle observations, guided by the predictions of both local and global numerical simulations, and placed in con- text by observations from far and extreme ultraviolet (FUV, EUV), hard X-ray, and energetic neutral atom imagers (ENA). Each proposed interaction mechanism (e.g., steady or transient magnetic reconnection, local or global magnetic reconnection, ion pick-up, or the KelvinHelmholtz instability) generates diagnostic plasma density structures. The significance of each mechanism to the overall interaction (as measured in terms of atmospheric/ionospheric loss at comets, Venus, and Mars or global magnetospheric/ionospheric convection at Earth) remains to be determined but can be evaluated on the basis of how often the density signatures that it generates are observed as a function of solar wind conditions. This paper reviews efforts to image the diagnostic plasma density structures in the soft (low energy, 0.1-2.0 keV) X-rays produced when high charge state solar wind ions exchange electrons with the exospheric neutrals surrounding solar system obstacles. The introduction notes that theory, local, and global simulations predict the characteristics of plasma boundaries such the bow shock and magnetopause (including location, density gradient, and motion) and regions such as the magnetosheath (including density and width) as a function of location, solar wind conditions, and the particular mechanism operating. In situ measurements confirm the existence of time-and spatial-dependent plasma density structures like the bow shock, magnetosheath, and magnetopause/ionopause at Venus, Mars, comets, and the Earth. However, in situ measurements rarely suffice to determine the global extent of these density structures or their global variation as a function of solar wind conditions, except in the form of empirical studies based on observations from many different times and solar wind conditions. Remote sensing observations provide global information about auroral ovals (FUV and hard X-ray), the terrestrial plasmasphere (EUV), and the terrestrial ring current (ENA). ENA instruments with low energy thresholds (∼ 1 keV) have recently been used to obtain important information concerning the magnetosheaths of Venus, Mars, and the Earth. Recent technological developments make these magnetosheaths valuable potential targets for high-cadence wide-field-of-view soft X-ray imagers.Section 2 describes proposed dayside interaction mechanisms, including reconnection, the Kelvin-Helmholtz instability, and other processes in greater detail with an emphasis on the plasma density structures that they generate. It focuses upon the questions that remain as yet unanswered, such as the significanc...

show abstract

Section: Cometsmentioning

confidence: 99%

Imaging Plasma Density Structures in the Soft X-Rays Generated by Solar Wind Charge Exchange with Neutrals

et al. 2018

View full text Add to dashboard Cite

show abstract

“…During this period, attempts to detect the bow shock were mostly unsuccessful because the spacecraft most of the time orbited in the inner coma (see e.g. Simon Wedlund et al 2017). Recently, Gunell et al (2018) reported measurements from the Rosetta Plasma Consortium (RPC) instrument suite onboard Rosetta, which for the first time showed evidence that the cometary bow shock was in a formation process at a heliocentric distance of about 2.3 AU.…”

Section: Introductionmentioning

confidence: 99%

Hybrid modeling of cometary plasma environments

Alho

Wedlund

Nilsson

et al. 2019

A&A

Self Cite

View full text Add to dashboard Cite

Context. The ESA Rosetta probe has not seen direct evidence of a fully formed bow shock at comet 67P/Churyumov-Gerasimenko (67P). Ion spectrometer measurements of cometary pickup ions measured in the vicinity of the nucleus of 67P are available and may contain signatures of the large-scale plasma environment. Aims. The aim is to investigate the possibility of using pickup ion signatures to infer the existence or nonexistence of a bow shock-like structure and possibly other large-scale plasma environment features. Methods. A numerical plasma model in the hybrid plasma description was used to model the plasma environment of a comet. Simulated pickup ion spectra were generated for different interplanetary magnetic field conditions. The results were interpreted through test particle tracing in the hybrid simulation solutions. Results. Features of the observed pickup ion energy spectrum were reproduced, and the model was used to interpret the observation to be consistent with a shock-like structure. We identify (1) a spectral break related to the bow shock, (2) a mechanism for generating the spectral break, and (3) a dependency of the energy of the spectral break on the interplanetary magnetic field magnitude and bow shock standoff distance.

show abstract

“…This implies that in the simplistic assumption of a rectilinear motion along the Suncomet line of the incoming solar wind ions, the retrieved solar wind upstream flux will be underestimated by this method. Selfconsistent modeling taking into account all charge-changing reactions, using hybrid (Simon Wedlund et al 2017) or multi-fluid MHD models (Huang et al 2016), can overcome this caveat.…”

Section: Upstream Solar Wind Fluxmentioning

confidence: 99%

“…Comparison with in situ derived outgassing rates by the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis Comet Pressure Sensor (ROSINA-COPS) (Balsiger et al 2007) showed that with these simple assumptions, month-to-month differences between the RPC-ICA-inferred and ROSINA-measured water outgassing rates remained within a factor 2 − 3 (Hansen et al 2016). In parallel, using a new quasi-neutral hybrid model of the cometary plasma environment, Simon Wedlund et al (2017) studied the interplay between ionization processes in the formation of boundaries at comet 67P. They showed that CX plays a major role at large cometocentric distances (> 1000 km at a heliocentric distance of 1.3 AU), whereas photoionization and electron ionization (sometimes referred to as "electron impact ionization") is the main source of new cometary ions in the inner coma (Bodewits et al 2016).…”

Section: Introductionmentioning

confidence: 99%

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

Hybrid modelling of cometary plasma environments

Cited by 44 publications

References 112 publications

Imaging Plasma Density Structures in the Soft X-Rays Generated by Solar Wind Charge Exchange with Neutrals

Imaging Plasma Density Structures in the Soft X-Rays Generated by Solar Wind Charge Exchange with Neutrals

Hybrid modeling of cometary plasma environments

Solar wind charge exchange in cometary atmospheres

Contact Info

Product

Resources

About