Distribution d’intensité dans la tête d’une comète

Haser, L.

doi:10.3406/barb.1957.68714

Cited by 78 publications

(7 citation statements)

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“…To cover a range of solar wind velocities, cross sections for particle impact speeds between 200 km/s and 1,000 km/s are included. The ratio of the ion flux lost due to charge‐exchange

{F}_{{X}^{n+}}\left(\bar{r}\right)

to the initial solar wind flux

{F}_{X}^{SW}

is:

{R}_{X}^{SW}\left(\bar{r}\right)=\frac{{F}_{{X}^{n+}}\left(\bar{r}\right)}{{F}_{X}^{SW}}={e}^{-{\sigma }_{CX}\,{I}_{n}\left(\bar{r}\right)}

The column density of neutrals along the solar wind ion trajectory is defined as a line of sight integration:

{I}_{n}\left(\bar{r}\right)=\int \nolimits_{\bar{r}}^{\infty }{n}_{n}(r)\ dr

The neutral gas density n n is described by a simple spherically symmetric model (Haser, 1957):

{n}_{n}(r)=\frac{Q}{4\pi {r}^{2}{u}_{n}}

where u n = 1,000 m/s is the neutral gas speed, Q is the gas production rate, and r is the cometocentric distance.…”

Section: Discussionmentioning

confidence: 99%

“…In addition, we use neutral gas densities provided by ROSINA‐COPS (Balsiger et al., 2007) to estimate the gas production rate. We assume a simple spherical model as detailed in Haser (1957) with 1 km/s neutral gas radial velocity to derive the gas production rate from the in situ measurements. All positions and fields are given in a Cometocentric Solar EQuatorial (CSEQ) coordinate system (ESA SPICE Service, 2019), unless otherwise noted.…”

Section: Observationsmentioning

confidence: 99%

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Solar Wind Protons in the Diamagnetic Cavity at Comet 67P/Churyumov‐Gerasimenko

et al. 2023

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The plasma environment at a comet can be divided into different regions with distinct plasma characteristics. Two such regions are the solar wind ion cavity, which refers to the part of the outer coma that does not contain any solar wind ions anymore; and the diamagnetic cavity, which is the region of unmagnetized plasma in the innermost coma. From theory and previous observations, it was thought that under usual circumstances no solar wind ion should be observable near or inside of the diamagnetic cavity. For the first time, we report on five observations that show that protons near solar wind energies can also be found inside the diamagnetic cavity. We characterize these proton signatures, where and when they occur, and discuss possible mechanisms that could lead to protons penetrating the inner coma and traversing the diamagnetic cavity boundary. By understanding these observations, we hope to better understand the interaction region of the comet with the solar wind under nonstandard conditions. The protons detected inside the diamagnetic cavity have directions and energies consistent with protons of solar wind origin. The five events occur only at intermediate gas production rates and low cometocentric distances. Charge transfer reactions, high solar wind dynamic pressure and a neutral gas outburst can be ruled out as causes. We suggest that the anomalous appearance of protons in the diamagnetic cavity is due to a specific solar wind configuration where the solar wind velocity is parallel to the interplanetary magnetic field, thus inhibiting mass‐loading and deflection.

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“…To cover a range of solar wind velocities, cross sections for particle impact speeds between 200 km/s and 1,000 km/s are included. The ratio of the ion flux lost due to charge‐exchange

{F}_{{X}^{n+}}\left(\bar{r}\right)

to the initial solar wind flux

{F}_{X}^{SW}

is:

{R}_{X}^{SW}\left(\bar{r}\right)=\frac{{F}_{{X}^{n+}}\left(\bar{r}\right)}{{F}_{X}^{SW}}={e}^{-{\sigma }_{CX}\,{I}_{n}\left(\bar{r}\right)}

The column density of neutrals along the solar wind ion trajectory is defined as a line of sight integration:

{I}_{n}\left(\bar{r}\right)=\int \nolimits_{\bar{r}}^{\infty }{n}_{n}(r)\ dr

The neutral gas density n n is described by a simple spherically symmetric model (Haser, 1957):

{n}_{n}(r)=\frac{Q}{4\pi {r}^{2}{u}_{n}}

where u n = 1,000 m/s is the neutral gas speed, Q is the gas production rate, and r is the cometocentric distance.…”

Section: Discussionmentioning

confidence: 99%

Section: Observationsmentioning

confidence: 99%

Solar Wind Protons in the Diamagnetic Cavity at Comet 67P/Churyumov‐Gerasimenko

et al. 2023

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“…However, it also depends on the heliocentric distance of the comet: comets at their perihelion have outgassing rates that are orders of magnitude higher than when they are several AU away from the sun. The neutral gas profile of a comet is frequently modelled based on the assumption of spherically symmetric outgassing where it follows a 1/r 2 profile (r: cometocentric distance) (Haser, 1957). This neutral gas gets ionised by photoionisation, charge exchange, and electronimpact-ionisation, and creates newborn cometary ions (e. g. Galand et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Explaining the Evolution of Ion Velocity Distributions at a low activity Comet

Moeslinger,

Gunell,

Nilsson

et al. 2024

Preprint

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At a low activity comet the plasma is distributed in an asymmetric way. The hybrid simulation code Amitis is used to look at the spatial evolution of ion velocity distribution functions (VDFs), from the upstream solar wind to within the comet magnetosphere where the solar wind is heavily mass-loaded by the cometary plasma. We find that the spatial structures of the ions and fields form a highly asymmetric, half-open induced magnetosphere. The VDFs of solar wind and cometary ions vary drastically for different locations in the comet magnetosphere. The shape of the VDFs differ for different species. The solar wind protons show high anisotropies that occasionally resemble partial rings, in particular at small cometocentric distances. A second, decoupled, proton population is also found. Solar wind alpha particles show similar anisotropies, although less pronounced and at different spatial scales. The VDFs of cometary ions are mostly determined by the structure of the electric field. We perform supplementary dynamic particle backtracing to understand the flow patterns of solar wind ions that lead to these anisotropic distributions. This tracing is needed to understand the origin of cometary ions in a given part of the comet magnetosphere. The particle tracing also aids in interpreting observed VDFs and relating them to spatial features in the electric and magnetic fields of the comet environment.

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“…This approach was introduced in Kramer et al 23 and Läuter et al, 9,24 it is briefly reviewed in Section 2, and it does away with the assumption of a spherical symmetric gas expansion of Haser-type models. 25 Kramer et al 23 retrieved surface maps showing the emission rates of neutral gas for three different time intervals and found a strong correlation between enhanced gas activity months before perihelion and locations of dust outbursts imaged around perihelion. 26 Läuter et al 24 extended this analysis to the major species H 2 O, CO 2 , CO and O 2 and to the entire duration of the Rosetta mission of two years.…”

Section: Introductionmentioning

confidence: 99%

Determination of the ice composition near the surface of comet 67P/Churyumov-Gerasimenko

Läuter¹,

Krämer

Rubin

et al. 2022

Preprint

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<p>During the apparition of comet 67P/Churyumov-Gerasimenko (67P/C-G) solar irradiation causes varying rates for sublimation of volatile species from the cometary nucleus. Because sublimation processes take place close to the cometary surface, the relative abundance of volatiles in the coma and the ice composition are related to each other. To quantify this relation we assume a model for the expansion of a collisionless gas from the surface into the surrounding space. We use an inverse model approach to relate the in situ measurements of gas densities from the two Rosetta instruments COPS (COmet Pressure Sensor) and DFMS (Double Focusing Mass Spectrometer) at the positions of the spacecraft to the locations of surface gas emissions during the Rosetta mission 2014-2016. We assume the temporally integrated gas emissions to be representative for the ice composition close to the surface. Our analysis shows characteristic differences in the ice compositions between both hemispheres of 67P/C-G. In particular CO2 ice has a reduced abundance on the northern hemisphere. In contrast to the hemispherical differences, the two lobes do not show significant differences in terms of their ice composition.</p>

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Distribution d’intensité dans la tête d’une comète

Abstract: The radial distribution of molecules in the head of a comet is investigated theoretically. Formulae for comparison with the observations are given.

Cited by 78 publications

References 0 publications

Solar Wind Protons in the Diamagnetic Cavity at Comet 67P/Churyumov‐Gerasimenko

Solar Wind Protons in the Diamagnetic Cavity at Comet 67P/Churyumov‐Gerasimenko

Explaining the Evolution of Ion Velocity Distributions at a low activity Comet

Determination of the ice composition near the surface of comet 67P/Churyumov-Gerasimenko

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