First in situ plasma and neutral gas measurements at comet Halley

Gringauz, K. I.; Gombosi, T. I.; Remizov, A. P.; Apáthy, I.; Szemerey, I.; Веригин, М. И.; Denchikova, L. I.; Dyachkov, A.; Keppler, E.; Klimenko, I. N.; Richter, A. K.; Somogyi, A.; Szegö, K.; Szendro, S.; Tátrallyay, M.; Varga, A.; Vladimirova, G. A.

doi:10.1038/321282a0

Cited by 207 publications

(82 citation statements)

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“…T i \ (3/32)m i v s 2/k B A (assuming equipartition between ions and magnetic Ðeld) gives K. On these grounds, we might expect lower T e > 3 ] 106 hybrid wave acceleration to have ceases in Cas A since the electrons have been heated by collisional processes to T e D 4 ] 107K. On the other hand, this criterion appears not to be met for the plasma conditions near the nucleus of comet Halley, where lower hybrid waves and their associated electron distribution function were in fact observed in situ in 1986 (Gringauz et al 1986 ;Klimov et al 1986), suggesting possibly that it is somewhat naive. From the condition that the electron Landau damping rate be we derive which is equivalent to the Ðrst inequality if but > ) LH , k B T e > m e ) LH 2 /k A 2 , k A /k \ cos h \ u pi /u pe extends to higher electron temperatures for cos h ] 0, which would be more consistent with observations.…”

Section: A2 Kinetic Growth Rate and Accelerated Electron Distributionmentioning

confidence: 97%

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Accelerated Electrons in Cassiopeia A: An Explanation for the Hard X‐Ray Tail

Laming

2001

ApJ

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We propose a model for the hard X-ray ([10 keV) emission observed from the supernova remnant Cas A. Lower hybrid waves are generated in strong (mG) magnetic Ðelds, generally believed to reside in this remnant, by shocks reÑected from density inhomogeneities. These then accelerate electrons to energies of several tens of keV. Around 4% of the X-rayÈemitting plasma electrons need to be in this accelerated distribution, which extends up to electron velocities of order the electron speed and is Alfven directed along magnetic Ðeld lines. Bremsstrahlung from these electrons produces the observed hard X-ray emission. Such waves and accelerated electrons have been observed in situ at comet Halley, and we discuss the viability of the extrapolation from this case to the parameters relevant to Cas A.

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Section: A2 Kinetic Growth Rate and Accelerated Electron Distributionmentioning

confidence: 97%

“…around the nucleus of comet Halley, where lower hybrid waves and accelerated electrons were directly detected in situ (Gringauz et al 1986 ;Klimov et al 1986). They observed rad s~1 and cm~3 giving ) LH D 100 n e^3 00 while K and…”

Section: T He T Hermal Electron T Emperaturementioning

confidence: 99%

Accelerated Electrons in Cassiopeia A: An Explanation for the Hard X‐Ray Tail

Laming

2001

ApJ

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“…At the moment of the VEGA 1 flyby, the total neutral gas production rate was evaluated as 1.3 x 1030 sec i by the PLASMAG-1 experiment (Gringauz et al 1986) and 103° sec ~ by the NGE experiment (Curtis et al 1986). Compared with our H20 production rate determination, this confirms that water is the dominant volatile product of the cometary nucleus.…”

Section: 5)mentioning

confidence: 99%

The 2.5–12 μm spectrum of comet halley from the IKS-VEGA experiment

Combes

Мороз

Crovisier

et al. 1988

Icarus

183

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The infrared instrument IKS flown on board the VEGA space probes was designed for the detection of emission bands of parent molecules, and for a measurement of the size and temperature of the thermal emitting nuclear region. The instrument had three channels with cooled detectors: an "imaging channel" designed to modulate the signal of the nucleus and two spectroscopic channels operating at 2.5-5 and 6-12 #m, respectively, equipped with circular variable filters of resolving power ~50. This paper presents and discusses the results from the spectral channels. On VEGA 1, usable spectra were obtained at distances D from the comet nucleus ranging from 250,000 to 40,000 km corresponding to fields of view 4000 and 700 km in diameter, respectively. The important internal background signal caused by the instrument itself, which could not be cooled, had to be eliminated. Since no sky chopping was performed, we obtain difference spectra between the current spectrum and a reference spectrum with little or no cometary signal taken at the beginning of the observing sequence (D ~ 200,000 km). Final discrimination between cometary signal and instrumental background is achieved using their different time evolution, since the instrumental background is proportional to the slow temperature drift of the instrument, and the cometary signal due to parent molecules or dust grains is expected to vary in first order as D -I.The 2.5-5 ~m IKS spectra definitely show strong narrow signals at 2.7 and 4.25 ~m, attributed to the ~; vibrational bands of H20 and CO2, respectively, and a broader signal in the region 3.2-3.5/tm, which may be attributed to CH-bearing molecules. All these signals present the expected D -1 intensity variation. Weaker emission features at 3.6 and 4.7 #m could correspond to the vl and l,s bands of H2CO and the (1 -0) band of CO, respectively. Molecular production rates are derived from the observed emissions, assuming that they are due to resonance fluorescence excited by the Sun's infrared radiation. For the strong bands of H20 and CO2, the rovibrational lines are optically thick, and radiative transfer is taken into account. We derive production rates, at the moment of the VEGA 1 flyby, of ~10 a° sec -1 for H20, ~2.7 x 1028 sec -1 for CO2, ~5 × 1028 sec -l for CO, and 4 xl02s sec -~ for H2CO, if attributions to CO and H2CO are correct. The production rate of carbon atoms in CH-bearing molecules is -9 x 10 29 sec -1 assuming fluorescence of molecules in the gas phase, but could be much less if the 3.2-3.5 pm emission is attributed to C-H stretch in polycyclic aromatic hydrocarbons or small organic grains. In addition, marginal features are present at 4.85 and 4.45 #m, tentatively attributed to OCS and molecules with the CN group, respectively. Broad absorption at 2.8-3.0 #m, as well as a narrow emission at 3.15/tm, which follow well the D -1 intensity variation, might be due to water ice. Emission at 2.8 /~m is also possibly present, and 404 0019-1035/88 $3.00 Copyright ,L~ 1988 by Academic Press, Inc. All rights o...

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“…Gas in the coma moves radially away from the nucleus, and a substantial fraction is eventually ionized through photoionization from solar ultraviolet radiation, charge exchange with the solar wind, or electron impact ionization (Cravens 1987;Cravens et al 1987;Gan & Cravens 1990). In situ observations of cometary ionospheres have been made at comets 1P/Halley (Gringauz et al 1986;Johnstone 1990;Larson et al 1992), Giacobini-Zinner Thomsen et al 1986;Zwickl et al 1986), Grigg-Skjellerup (Reme et al 1993), 19P/Borrelly (Nordholt et al 2003;Young et al 2004), and recently at 67P/Churyumov-Gerasimenko (67P) Burch et al 2015;Clark et al 2015;Edberg et al 2015;Goldstein et al 2015;Nilsson et al 2015a;Behar et al 2016).…”

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confidence: 99%