Solar wind charge exchange in cometary atmospheres

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 (He2+, He+, He0) and (H+, H0, H−) on solar wind parameters at comet 67P. We show that double charge exchange for the He2+−H2O 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.

Download Full-text

Solar wind charge exchange in cometary atmospheres

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834881 ◽

2019 ◽

Vol 630 ◽

pp. A37 ◽

Cited By ~ 6

Author(s):

Cyril Simon Wedlund ◽

Etienne Behar ◽

Hans Nilsson ◽

Markku Alho ◽

Esa Kallio ◽

...

Keyword(s):

Solar Wind ◽

Charge Exchange ◽

Cross Sections ◽

Extreme Ultraviolet ◽

Solar Wind Plasma ◽

Analytical Models ◽

Sharp Drop ◽

Solar Wind Charge Exchange ◽

Comet 67P

Context. Solar wind charge-changing reactions are of paramount importance to the physico-chemistry of the atmosphere of a comet. The ESA/Rosetta mission to comet 67P/Churyumov-Gerasimenko (67P) provides a unique opportunity to study charge-changing processes in situ. Aims. To understand the role of these reactions in the evolution of the solar wind plasma and interpret the complex in situ measurements made by Rosetta, numerical or analytical models are necessary. Methods. We used an extended analytical formalism describing solar wind charge-changing processes at comets along solar wind streamlines. The model is driven by solar wind ion measurements from the Rosetta Plasma Consortium-Ion Composition Analyser (RPC-ICA) and neutral density observations from the Rosetta Spectrometer for Ion and Neutral Analysis-Comet Pressure Sensor (ROSINA-COPS), as well as by charge-changing cross sections of hydrogen and helium particles in a water gas. Results. A mission-wide overview of charge-changing efficiencies at comet 67P is presented. Electron capture cross sections dominate and favor the production of He and H energetic neutral atoms (ENAs), with fluxes expected to rival those of H+ and He2+ ions. Conclusions. Neutral outgassing rates are retrieved from local RPC-ICA flux measurements and match ROSINA estimates very well throughout the mission. From the model, we find that solar wind charge exchange is unable to fully explain the magnitude of the sharp drop in solar wind ion fluxes observed by Rosetta for heliocentric distances below 2.5 AU. This is likely because the model does not take the relative ion dynamics into account and to a lesser extent because it ignores the formation of bow-shock-like structures upstream of the nucleus. This work also shows that the ionization by solar extreme-ultraviolet radiation and energetic electrons dominates the source of cometary ions, although solar wind contributions may be significant during isolated events.

Download Full-text

Solar wind charge exchange: an astrophysical nuisance

The Astronomy and Astrophysics Review ◽

10.1007/s00159-018-0114-0 ◽

2018 ◽

Vol 27 (1) ◽

Cited By ~ 6

Author(s):

K. D. Kuntz

Keyword(s):

Solar Wind ◽

Charge Exchange ◽

Solar Wind Charge Exchange

Download Full-text

Deriving CME volume and density from remote sensing data

10.5194/egusphere-egu21-2535 ◽

2021 ◽

Author(s):

Manuela Temmer ◽

Lukas Holzknecht ◽

Mateja Dumbovic ◽

Bojan Vrsnak ◽

Nishtha Sachdeva ◽

...

Keyword(s):

Solar Wind ◽

Solar Wind Speed ◽

Remote Sensing Data ◽

Propagation Speed ◽

Solar Wind Density ◽

Sheath Region ◽

Pile Up ◽

Mass Ejection ◽

Interplanetary Propagation

<p>Using combined STEREO-SOHO white-light data, we present a method to determine the&#160;volume and density of a coronal mass ejection (CME) by applying the graduated cylindrical&#160;shell model (GCS) and deprojected mass derivation. Under the assumption that the CME &#160;mass is roughly equally distributed within a specific volume, we expand the CME self-similarly and calculate the CME density for distances close to the Sun (15&#8211;30 Rs) and at 1 AU.&#160;The procedure is applied on a sample of 29 well-observed CMEs and compared to their&#160;interplanetary counterparts (ICMEs). Specific trends are derived comparing calculated and&#160;in-situ measured proton densities at 1 AU, though large uncertainties are revealed due to&#160;the unknown mass and geometry evolution: i) a moderate correlation for the magnetic&#160;structure having a mass that stays rather constant and ii) a weak&#160;correlation for the sheath density by assuming the sheath region is an extra mass&#160;- as expected for a mass pile-up process - that is in its amount comparable to the initial CME&#160;deprojected mass. High correlations are derived between in-situ measured sheath density&#160;and the solar wind density and solar wind speed as measured 24&#160;hours ahead of the arrival of the disturbance. This gives additional confirmation that the&#160;sheath-plasma indeed stems from piled-up solar wind material. While the CME&#160;interplanetary propagation speed is not related to the sheath density, the size of the CME&#160;may play some role in how much material is piled up.</p>

Download Full-text

Ion energy and momentum flux near the cometopause of Comet 67P/Churyumov-Gerasimenko

10.5194/egusphere-egu21-14280 ◽

2021 ◽

Author(s):

Hayley Williamson ◽

Hans Nilsson ◽

Anja Moslinger ◽

Sofia Bergman ◽

Gabriella Stenberg-Wieser

Keyword(s):

Solar Wind ◽

Complex Dynamics ◽

Distribution Functions ◽

Transitional Period ◽

Ion Energy ◽

Rosetta Mission ◽

Before And After ◽

Composition Analyzer ◽

Energy And Momentum ◽

Comet 67P

<p>Defined as the region where the plasma interaction region of a comet goes from being solar wind-dominated to cometary ion-dominated, the cometopause is a region of comingling plasmas and complex dynamics. The Rosetta mission orbited comet 67P/Churyumov-Gerasimenko for roughly two years. During this time, the cometopause was observed by the Ion Composition Analyzer (ICA), part of the Rosetta Plasma Consortium (RPC), before and after the spacecraft was in the solar wind ion cavity, defined as the region where no solar wind ions were measured. Data from ICA shows that solar wind and cometary ions have similar momentum and energy flux moments during this transitional period, indicating mass loading and deflection of the solar wind. We examine higher order moments and distribution functions for the solar wind and cometary species between December 2015 and March 2016. The behavior of the solar wind protons indicates that in many cases these protons are deflected in a sunward direction, while the cometary ions continue to move predominately antisunward. By studying the distribution functions of the protons during these time periods, it is possible to see a non-Maxwellian energy distribution. This can inform on the nature of the cometopause boundary and the energy transfer mechanisms at play in this region.</p>

Download Full-text

On acceleration of <1 MeV/n He ions in the corotating compression regions near 1 AU: STEREO observations

Annales Geophysicae ◽

10.5194/angeo-27-3677-2009 ◽

2009 ◽

Vol 27 (9) ◽

pp. 3677-3690 ◽

Cited By ~ 13

Author(s):

R. Bučík ◽

U. Mall ◽

A. Korth ◽

G. M. Mason

Keyword(s):

Solar Wind ◽

Total Pressure ◽

Solar Wind Speed ◽

Shock Acceleration ◽

Model Parameters ◽

Corotating Interaction Region ◽

Reverse Shock ◽

Compression Region ◽

Model Predictions

Abstract. Observations of multi-MeV corotating interaction region (CIR) ions are in general consistent with models of CIR shock acceleration and transport. The presence of suprathermal particles near 1 AU in unshocked compression regions is not adequately explained. Nonetheless, more recent works demonstrate that unshocked compression regions associated with CIRs near 1 AU could energize particles. In the energy range from ~0.1 to ~1 MeV/n we investigate CIR events observed in 2007–2008 by the STEREO A and B spacecraft. We treat the predictions of compression acceleration by comparing the observed ion intensities with the model parameters. These observations show that the ion intensity in CIR events with in-situ reverse shock is well organized by the parameters which characterize the compression region itself, like compression width, solar wind speed gradients and the total pressure. In turn, for CIR events with the absence of the shocks the model predictions are not fulfilled.

Download Full-text