Spacecraft charging near Enceladus

Hsu, Hsiang-Wen; Horányi, M.; Kempf, S.; Grün, E.

doi:10.1029/2012gl050999

Cited by 11 publications

(13 citation statements)

References 35 publications

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“…The knowledge of the electron and ion densities helps to constrain the dust size distributions measured by different instruments during the Enceladus flybys and E ring crossings [ Yaroshenko et al ., ; Shafiq et al ., ; Morooka et al ., ; Hill et al ., ]. An accurate electron density also helps to understand the dusty plasma dynamics in the vicinity of Enceladus, which serves as a natural laboratory for studying the dust‐plasma interaction [ Morooka et al ., ; Hsu et al ., , ].…”

Section: Discussionmentioning

confidence: 99%

Electron density inside Enceladus plume inferred from plasma oscillations excited by dust impacts

Gurnett

Kurth

et al. 2014

JGR Space Physics

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Enceladus' southern plume is one of the major discoveries of the Cassini mission. The water neutrals and water ice particles (dust) ejected by the cryovolcanic activity populate Saturn's E ring and the neutral torus, and they interact with the plasma environment of Saturn's magnetosphere. The plasma neutrality inside Enceladus' plume has been shown by the Langmuir probe measurement to be modified by the presence of the dust particles. We present an independent method of determining the electron density inside the plume. Sometimes, after dust impacts, plasma oscillations (ringing) were detected by the Cassini Radio and Plasma Wave Science instrument. The frequencies of these oscillations have been shown to be consistent with the local plasma frequency, thus providing a measurement of the local electron density.

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Section: Discussionmentioning

confidence: 99%

Electron density inside Enceladus plume inferred from plasma oscillations excited by dust impacts

Gurnett

Kurth

et al. 2014

JGR Space Physics

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“…At higher latitudes and farther away from Saturn, mostly positive pulses were observed. This is consistent with the theory and observation that Cassini spacecraft is negatively charged in the cold dense plasma torus and positively charged in the hot tenuous plasma of the outer magnetosphere [ Wahlund et al ., , ; Morooka et al ., , ; Gustafsson and Wahlund , ; Hsu et al ., , ]. Figure (right) can be compared with Figure c of Wahlund et al .…”

Section: Onboard Dust Detectionmentioning

confidence: 98%

Properties of dust particles near Saturn inferred from voltage pulses induced by dust impacts on Cassini spacecraft

Gurnett

Kŭrth

et al. 2014

JGR Space Physics

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The Cassini Radio and Plasma Wave Science (RPWS) instrument can detect dust particles when voltage pulses induced by the dust impacts are observed in the wideband receiver. The size of the voltage pulse is proportional to the mass of the impacting dust particle. For the first time, the dust impacts signals measured by dipole and monopole electric antennas are compared, from which the effective impact area of the spacecraft is estimated to be 4 m 2 . In the monopole mode, the polarity of the dust impact signal is determined by the spacecraft potential and the location of the impact (on the spacecraft body or the antenna), which can be used to statistically infer the charge state of the spacecraft. It is shown that the differential number density of the dust particles near Saturn can be characterized as a power law dn/dr ∝ r μ , where μ~À 4 and r is the particle size. No peak is observed in the size distribution, contrary to the narrow size distribution found by previous studies. The RPWS cumulative dust density is compared with the Cosmic Dust Analyzer High Rate Detector measurement. The differences between the two instruments are within the range of uncertainty estimated for RPWS measurement. The RPWS onboard dust recorder and counter data are used to map the dust density and spacecraft charging state within Saturn's magnetosphere.

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“…The Langmuir probe (RPC‐LAP) on Rosetta indicated that the spacecraft (s/c) had an electrical potential relative to the ambient plasma of about V s/c ≈ −5 V to −20 V [ Edberg et al ., ; Odelstad et al ., ]. It is well‐known that spacecraft, dust grains, etc., can acquire electrical charge (and thus potential) in space due to several types of charging currents [ Hsu et al ., ], including ambient plasma electron and ion currents and photocurrents from absorption of solar photons. The cometary nucleus itself at 3 AU should have an electrical potential.…”

Section: The Rosetta Ion and Electron Spectrometer (Ies) And Datamentioning

confidence: 99%

Suprathermal electrons near the nucleus of comet 67P/Churyumov‐Gerasimenko at 3 AU: Model comparisons with Rosetta data

et al. 2016

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Observations of the coma near the nucleus of comet 67P/Churyumov‐Gerasimenko (67P) made by the IES (Ion and Electron Sensor) instrument onboard the Rosetta Orbiter during late 2014 showed that electron fluxes greatly exceeded solar wind electron fluxes. The IES is part of the Rosetta Plasma Consortium. This paper reports on electron energy spectra measured by IES near the nucleus as well as approximate densities and average energies for the suprathermal electrons when the comet was at a heliocentric distance of about 3 AU. Comparisons are made with electron densities measured by other instruments. The high electron densities observed (e.g., ne ≈ 10–100 cm−3) must be associated with the cometary ion density enhancement created mainly by the photoionization of cometary gas by solar radiation; there are other processes that also contribute. Quasineutrality requires that the electron and ion densities be the same, and under certain conditions an ambipolar electric field is required to achieve quasi‐neutrality. We present the results of a test particle model of cometary ion pickup by the solar wind and a two‐stream electron transport code and use these results to interpret the IES data. We also estimate the effects on the electron spectrum of a compression of the electron fluid parcel. The electrons detected by IES can have energies as high as about 100–200 eV near the comet on some occasions, in which case the hot electrons can significantly enhance ionization rates of neutrals via impact ionization.

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Spacecraft charging near Enceladus

Cited by 11 publications

References 35 publications

Electron density inside Enceladus plume inferred from plasma oscillations excited by dust impacts

Electron density inside Enceladus plume inferred from plasma oscillations excited by dust impacts

Properties of dust particles near Saturn inferred from voltage pulses induced by dust impacts on Cassini spacecraft

Suprathermal electrons near the nucleus of comet 67P/Churyumov‐Gerasimenko at 3 AU: Model comparisons with Rosetta data

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