Impact of a cometary outburst on its ionosphere

Hajra, Rajkumar; Henri, Pierre; Vallières, Xavier; Galand, M.; Héritier, K. L.; Eriksson, Anders; Odelstad, Elias; Edberg, Niklas J. T.; Burch, J. L.; Broiles, T. W.; Goldstein, R.; Glaßmeier, K.‐H.; Richter, Ingo; Goetz, Charlotte; Tsurutani, B. T.; Nilsson, Hans; Altwegg, Kathrin; Rubin, Martin

doi:10.1051/0004-6361/201730591

Cited by 26 publications

(29 citation statements)

References 53 publications

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“…[10-30] mHz frequency range, it is clearly lower by a factor of 5-10 at higher frequencies. This is in good agreement with the weakening of the ∼10−100 mHz magnetic field fluctuations previously noted in Hajra et al (2017).…”

Section: Magnetic-field Oscillation Properties From Rpc-mag Measurementssupporting

confidence: 92%

“…In response to the outburst, the neutral density increased by a factor of ∼2 and the local plasma density increased by a factor of ∼3. The local magnetic field exhibited a slight increase in amplitude (∼5 nT) and an abrupt rotation (36.4 • ) in response to the outburst (see Hajra et al 2017). A weakening of ∼10-100 mHz magnetic field fluctuations was also noted during the outburst, suggesting an alteration of the origin of the wave activity.…”

Section: Introductionmentioning

confidence: 93%

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Properties of the singing comet waves in the 67P/Churyumov-Gerasimenko plasma environment as observed by the Rosetta mission

Breuillard

Henri

Volwerk

et al. 2019

A&A

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Using in situ measurements from different instruments on board the Rosetta spacecraft, we investigate the properties of the newly discovered low-frequency oscillations, known as singing comet waves, that sometimes dominate the close plasma environment of comet 67P/Churyumov-Gerasimenko. These waves are thought to be generated by a modified ion-Weibel instability that grows due to a beam of water ions created by water molecules that outgass from the comet. We take advantage of a cometary outburst event that occurred on 2016 February 19 to probe this generation mechanism. We analyze the 3D magnetic field waveforms to infer the properties of the magnetic oscillations of the cometary ion waves. They are observed in the typical frequency range (~50 mHz) before the cometary outburst, but at ~20 mHz during the outburst. They are also observed to be elliptically right-hand polarized and to propagate rather closely (~0−50°) to the background magnetic field. We also construct a density dataset with a high enough time resolution that allows us to study the plasma contribution to the ion cometary waves. The correlation between plasma and magnetic field variations associated with the waves indicates that they are mostly in phase before and during the outburst, which means that they are compressional waves. We therefore show that the measurements from multiple instruments are consistent with the modified ion-Weibel instability as the source of the singing comet wave activity. We also argue that the observed frequency of the singing comet waves could be a way to indirectly probe the strength of neutral plasma coupling in the 67P environment.

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Section: Magnetic-field Oscillation Properties From Rpc-mag Measurementssupporting

confidence: 92%

Section: Introductionmentioning

confidence: 93%

Properties of the singing comet waves in the 67P/Churyumov-Gerasimenko plasma environment as observed by the Rosetta mission

Breuillard

Henri

Volwerk

et al. 2019

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“…The model uses time-varying electron-impact ionization frequency based on RPC-IES measurements, photoionization frequency obtained from Thermosphere Ionosphere Mesophere Energetics and Dynamics-Solar EUV Experiment (TIMED-SEE, Woods et al 2005) and interpolated to comet 67P along with cometary neutral density and neutral composition measured by the ROSINA-COPS (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis-COmet Pressure Sensor) and ROSINA-DFMS (Double Focusing Mass Spectrometer) instruments (Balsiger et al 2007), respectively. The respective contributions of photoionization and electron-impact ionization are reported to be highly variable (see Galand et al 2016;Heritier et al 2017;Hajra et al 2017b).…”

Section: What Is the Source Of The Large Cometary Plasma Enhancement mentioning

confidence: 99%

Cometary plasma response to interplanetary corotating interaction regions during 2016 June–September: a quantitative study by the Rosetta Plasma Consortium

Hajra

Henri

Myllys

et al. 2018

Monthly Notices of the Royal Astronomical Society

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Four interplanetary corotating interaction regions (CIRs) were identified during 2016 June-September by the Rosetta Plasma Consortium (RPC) monitoring in situ the plasma environment of the comet 67P/Churyumov-Gerasimenko (67P) at heliocentric distances of ∼3-3.8 au. The CIRs, formed in the interface region between low-and high-speed solar wind streams with speeds of ∼320-400 km s −1 and ∼580-640 km s −1 , respectively, are characterized by relative increases in solar wind proton density by factors of ∼13-29, in proton temperature by ∼7-29, and in magnetic field by ∼1-4 with respect to the pre-CIR values. The CIR boundaries are well defined with interplanetary discontinuities. Out of 10 discontinuities, four are determined to be forward waves and five are reverse waves, propagating at ∼5-92 per cent of the magnetosonic speed at angles of ∼20 •-87 • relative to ambient magnetic field. Only one is identified to be a quasi-parallel forward shock with magnetosonic Mach number of ∼1.48 and shock normal angle of ∼41 •. The cometary ionosphere response was monitored by Rosetta from cometocentric distances of ∼4-30 km. A quiet time plasma density map was developed by considering dependences on cometary latitude, longitude, and cometocentric distance of Rosetta observations before and after each of the CIR intervals. The CIRs lead to plasma density enhancements of ∼500-1000 per cent with respect to the quiet time reference level. Ionospheric modelling shows that increased ionization rate due to enhanced ionizing (>12-200 eV) electron impact is the prime cause of the large cometary plasma density enhancements during the CIRs. Plausible origin mechanisms of the cometary ionizing electron enhancements are discussed.

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“…This study is complementary to previous studies of other types of transient solar forcing, for instance, solar wind pressures pulses such as coronal mass ejections (CMEs) or corotating interaction regions (CIR), which have been shown to have large effects on the plasma environment of comet 67P (Edberg et al 2016b,a;Hajra et al 2018;Noonan et al 2018;Goetz et al 2018). The results will also complement the understanding of the variability of a cometary plasma environment, which is affected by a number of short-time scale processes (minutes to hours) that include, for example, cometary outbursts (Grün et al 2016;Hajra et al 2017), the changing amount of cold plasma (Eriksson et al 2017;Engelhardt et al 2018), plasma waves (Volwerk et al 2016;André et al 2017), and transient structures in the magnetic field, such as current sheets and the diamagnetic cavity (Volwerk et al 2017;.…”

Section: Introductionmentioning

confidence: 86%

Solar flares observed by Rosetta at comet 67P/Churyumov-Gerasimenko

Edberg

Johansson

Eriksson

et al. 2019

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Context. The Rosetta spacecraft made continuous measurements of the coma of comet 67P/Churyumov-Gerasimenko (67P) for more than two years. The plasma in the coma appeared very dynamic, and many factors control its variability. Aims. We wish to identify the effects of solar flares on the comet plasma and also their effect on the measurements by the Langmuir Probe Instrument (LAP). Methods. To identify the effects of flares, we proceeded from an existing flare catalog of Earth-directed solar flares, from which a new list was created that only included Rosetta-directed flares. We also used measurements of flares at Mars when at similar longitudes as Rosetta. The flare irradiance spectral model (FISM v.1) and its Mars equivalent (FISM-M) produce an extreme-ultraviolet (EUV) irradiance (10-120 nm) of the flares at 1 min resolution. LAP data and density measurements obtained with the Mutual Impedence Probe (MIP) from the time of arrival of the flares at Rosetta were examined to determine the flare effects. Results. From the vantage point of Earth, 1504 flares directed toward Rosetta occurred during the mission. In only 24 of these, that is, 1.6%, was the increase in EUV irradiance large enough to cause an observable effect in LAP data. Twenty-four Mars-directed flares were also observed in Rosetta data. The effect of the flares was to increase the photoelectron current by typically 1-5 nA. We find little evidence that the solar flares increase the plasma density, at least not above the background variability. Conclusions. Solar flares have a small effect on the photoelectron current of the LAP instrument, and they are not significant in comparison to other factors that control the plasma density in the coma. The photoelectron current can only be used for flare detection during periods of calm plasma conditions.

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Impact of a cometary outburst on its ionosphere

Cited by 26 publications

References 53 publications

Properties of the singing comet waves in the 67P/Churyumov-Gerasimenko plasma environment as observed by the Rosetta mission

Properties of the singing comet waves in the 67P/Churyumov-Gerasimenko plasma environment as observed by the Rosetta mission

Cometary plasma response to interplanetary corotating interaction regions during 2016 June–September: a quantitative study by the Rosetta Plasma Consortium

Solar flares observed by Rosetta at comet 67P/Churyumov-Gerasimenko

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