Birth of a comet magnetosphere: A spring of water ions

Nilsson, Hans; Wieser, Gabriella Stenberg; Béhar, Etienne; Wedlund, Cyril Simon; Gunell, H.; Yamauchi, M.; Lundin, R.; Barabash, S.; Wieser, Martin; Carr, C.; Cupido, E.; Burch, J. L.; Fedorov, A.; Sauvaud, J. A.; Koskinen, H.; Kallio, Esa; Lebreton, J. P.; Eriksson, Anders; Edberg, Niklas J. T.; Goldstein, R.; Henri, Pierre; Koenders, C.; Mokashi, P.; Németh, Zoltán; Richter, Ingo; Szegö, K.; Volwerk, M.; Vallat, C.; Rubin, Martin

doi:10.1126/science.aaa0571

Cited by 119 publications

(135 citation statements)

References 24 publications

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“…Plasma of cometary origin has been observed by the Ion Composition Analyzer (RPC-ICA) since 7 August 2014, at a distance of 100 km from the nucleus, in the form of water ions picked up by the solar wind electric field and accelerated toward the spacecraft perpendicular to the solar wind direction [Nilsson et al, 2015a]. Locally produced water ions, accelerated into the instrument by a negative spacecraft potential, were first detected by the Rosetta Ion and Electron Sensor (RPC-IES) on 19 August 2014 at a distance of ∼80 km from the nucleus [Goldstein et al, 2015].…”

Section: Introductionmentioning

confidence: 99%

Evolution of the plasma environment of comet 67P from spacecraft potential measurements by the Rosetta Langmuir probe instrument

Odelstad

Eriksson

Edberg

et al. 2015

Geophysical Research Letters

108

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We study the evolution of the plasma environment of comet 67P using measurements of the spacecraft potential from early September 2014 (heliocentric distance 3.5 AU) to late March 2015 (2.1 AU) obtained by the Langmuir probe instrument. The low collision rate keeps the electron temperature high (∼5 eV), resulting in a negative spacecraft potential whose magnitude depends on the electron density. This potential is more negative in the northern (summer) hemisphere, particularly over sunlit parts of the neck region on the nucleus, consistent with neutral gas measurements by the Cometary Pressure Sensor of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis. Assuming constant electron temperature, the spacecraft potential traces the electron density. This increases as the comet approaches the Sun, most clearly in the southern hemisphere by a factor possibly as high as 20–44 between September 2014 and January 2015. The northern hemisphere plasma density increase stays around or below a factor of 8–12, consistent with seasonal insolation change.

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Section: Introductionmentioning

confidence: 99%

Evolution of the plasma environment of comet 67P from spacecraft potential measurements by the Rosetta Langmuir probe instrument

Odelstad

Eriksson

Edberg

et al. 2015

Geophysical Research Letters

108

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“…Newly implanted ions (or fresh pickup ions) have been seen in several cometary environments, but most recently by the Rosetta spacecraft at comet 67P [3,7]. In Figure 3 we show data from the Rosetta Ion and Electron Spectrometer instrument plotted over the whole Rosetta mission since orbit insertion in August 2014 to September 2016.…”

Section: Stage 1 -Implanted Ionsmentioning

confidence: 99%

“…The implanted ions are seen well below the energy of the solar wind in the second panel (ions). Although there are intervals where acceleration from the initial pickup energy is seen (Stage 2), many intervals particularly at large heliocentric distance (beginning and end of the plot) are characterized by low energy (<10eV) ions [3,7].…”

Section: Stage 1 -Implanted Ionsmentioning

confidence: 99%

Pickup Particle Acceleration at Comets, Moons and Magnetospheres

Coates

2017

J. Phys.: Conf. Ser.

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Abstract. Ionisation of neutrals plays a key role in the plasma interactions of comets and moons, and in magnetospheres. Following ionisation, ions and electrons are 'picked up' in the plasma flow, initially accelerating along the electric field and then gyrating around the magnetic field. For an ion with mass m (amu) this leads to an acceleration of up to 4m times the energy of the flowing plasma. Further scattering in pitch angle and energy may increase the acceleration further. Here, we illustrate the process at work with relevant plasma measurements from comets including Rosetta's comet 67P, from Titan and near Enceladus and Rhea.

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“…Therefore, the ion flux measured by DFMS strongly depends on the magnetic field orientation, the direction to the comet, and the amount of deflection and energization that the ions experience in the pickup process before their arrival at the spacecraft. Nilsson et al (2015) described observational evidence at 67P of this energization in the initial phase of the pickup process. Broiles et al (2015) demonstrated that the deflection of the solar wind is a consequence of this initial pickup process.…”

Section: Conditions At the Comet From Octobermentioning

confidence: 99%

“…2. The direction of propagation is deflected somewhat from the Sun direction because of the cometary ion pickup process described in the introduction (see also Broiles et al 2015;Nilsson et al 2015). The He + distribution is produced by charge exchange of solar wind He 2+ with cometary neutrals (Shelley et al 1987;Burch et al 2015).…”

Section: Conditions At the Comet From Octobermentioning

confidence: 99%

ROSINA/DFMS and IES observations of 67P: Ion-neutral chemistry in the coma of a weakly outgassing comet

Fuselier

Altwegg

Balsiger

et al. 2015

A&A

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Context. The Rosetta encounter with comet 67P/Churyumov-Gerasimenko provides a unique opportunity for an in situ, up-close investigation of ion-neutral chemistry in the coma of a weakly outgassing comet far from the Sun. Aims. Observations of primary and secondary ions and modeling are used to investigate the role of ion-neutral chemistry within the thin coma. Methods. Observations from late October through mid-December 2014 show the continuous presence of the solar wind 30 km from the comet nucleus. These and other observations indicate that there is no contact surface and the solar wind has direct access to the nucleus. On several occasions during this time period, the Rosetta/ROSINA/Double Focusing Mass Spectrometer measured the low-energy ion composition in the coma. Organic volatiles and water group ions and their breakup products (masses 14 through 19), CO + , and CO + 2 (masses 28 and 44) and other mass peaks (at masses 26, 27, and possibly 30) were observed. Secondary ions include H 3 O + and HCO + (masses 19 and 29). These secondary ions indicate ion-neutral chemistry in the thin coma of the comet. A relatively simple model is constructed to account for the low H 3 O + /H 2 O + and HCO + /CO + ratios observed in a water dominated coma. Results from this simple model are compared with results from models that include a more detailed chemical reaction network. Results. At low outgassing rates, predictions from the simple model agree with observations and with results from more complex models that include much more chemistry. At higher outgassing rates, the ion-neutral chemistry is still limited and high HCO + /CO + ratios are predicted and observed. However, at higher outgassing rates, the model predicts high H 3 O + /H 2 O + ratios and the observed ratios are often low. These low ratios may be the result of the highly heterogeneous nature of the coma, where CO and CO 2 number densities can exceed that of water.

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Birth of a comet magnetosphere: A spring of water ions

Abstract: Abstract:The Rosetta mission has been designed to rendezvous with and escort comet 67P/Churyumov-Gerasimenko from a heliocentric distance of >3.6 AU, when the comet still has a low activity level, until perihelion passage at 1.25 AU where the comet reaches the maximum

Cited by 119 publications

References 24 publications

Evolution of the plasma environment of comet 67P from spacecraft potential measurements by the Rosetta Langmuir probe instrument

Evolution of the plasma environment of comet 67P from spacecraft potential measurements by the Rosetta Langmuir probe instrument

Pickup Particle Acceleration at Comets, Moons and Magnetospheres

ROSINA/DFMS and IES observations of 67P: Ion-neutral chemistry in the coma of a weakly outgassing comet

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