| 1. |
- Fray, Nicolas, et al.
(author)
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High-molecular-weight organic matter in the particles of comet 67P/Churyumov–Gerasimenko
- 2016
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In: Nature. - : Nature Publishing Group. - 0028-0836 .- 1476-4687. ; 538:7623, s. 72-74
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Journal article (peer-reviewed)abstract
- The presence of solid carbonaceous matter in cometary dust was established by the detection of elements such as carbon, hydrogen, oxygen and nitrogen in particles from comet 1P/Halley1, 2. Such matter is generally thought to have originated in the interstellar medium3, but it might have formed in the solar nebula—the cloud of gas and dust that was left over after the Sun formed4. This solid carbonaceous material cannot be observed from Earth, so it has eluded unambiguous characterization5. Many gaseous organic molecules, however, have been observed6, 7, 8, 9; they come mostly from the sublimation of ices at the surface or in the subsurface of cometary nuclei8. These ices could have been formed from material inherited from the interstellar medium that suffered little processing in the solar nebula10. Here we report the in situ detection of solid organic matter in the dust particles emitted by comet 67P/Churyumov–Gerasimenko; the carbon in this organic material is bound in very large macromolecular compounds, analogous to the insoluble organic matter found in the carbonaceous chondrite meteorites11, 12. The organic matter in meteorites might have formed in the interstellar medium and/or the solar nebula, but was almost certainly modified in the meteorites’ parent bodies11. We conclude that the observed cometary carbonaceous solid matter could have the same origin as the meteoritic insoluble organic matter, but suffered less modification before and/or after being incorporated into the comet.
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| 2. |
- Hilchenbach, Martin, et al.
(author)
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Mechanical and electrostatic experiments with dust particles collected in the inner coma of comet 67P by COSIMA onboard Rosetta
- 2017
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In: Philosophical Transactions. Series A. - : The Royal Society. - 1364-503X .- 1471-2962. ; 375:2097
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Journal article (peer-reviewed)abstract
- The in situ cometary dust particle instrument COSIMA (COmetary Secondary Ion Mass Analyser) onboard ESA's Rosetta mission has collected about 31 000 dust particles in the inner coma of comet 67P/Churyumov-Gerasimenko since August 2014. The particles are identified by optical microscope imaging and analysed by time-of-flight secondary ion mass spectrometry. After dust particle collection by low speed impact on metal targets, the collected particle morphology points towards four families of cometary dust particles. COSIMA is an in situ laboratory that operates remotely controlled next to the comet nucleus. The particles can be further manipulated within the instrument by mechanical and electrostatic means after their collection by impact. The particles are stored above 0°C in the instrument and the experiments are carried out on the refractory, ice-free matter of the captured cometary dust particles. An interesting particle morphology class, the compact particles, is not fragmented on impact. One of these particles was mechanically pressed and thereby crushed into large fragments. The particles are good electrical insulators and transform into rubble pile agglomerates by the application of an energetic indium ion beam during the secondary ion mass spectrometry analysis. This article is part of the themed issue 'Cometary science after Rosetta'. © 2017 The Authors.
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| 3. |
- Andriopoulou, Maria, et al.
(author)
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Plasma Density Estimates From Spacecraft Potential Using MMS Observations in the Dayside Magnetosphere
- 2018
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In: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 123:4, s. 2620-2629
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Journal article (peer-reviewed)abstract
- Using spacecraft potential observations with and without active spacecraft potential control (on/off) from the Magnetospheric Multiscale (MMS) mission, we estimate the average photoelectron emission as well as derive the plasma density information from spacecraft potential variations and active spacecraft potential control ion current. Such estimates are of particular importance especially during periods when the plasma instruments are not in operation and also when electron density observations with higher time resolution than the ones available from particle detectors are necessary. We compare the average photoelectron emission of different spacecraft and discuss their differences. We examine several time intervals when we performed our density estimations in order to understand the strengths and weaknesses of our data set. We finally compare our derived density estimates with the plasma density observations provided by plasma detectors onboard MMS, whenever available, and discuss the overall results. The estimated electron densities should only be used as a proxy of the electron density, complimentary to the plasma moments derived by plasma detectors, especially when the latter are turned off or when higher time resolution observations are required. While the derived data set can often provide valuable information about the plasma environment, the actual values may often be very far from the actual plasma density values and should therefore be used with caution.
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| 4. |
- Engwall, Erik, 1977-, et al.
(author)
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Low-energy (order 10 eV) ion flow in the magnetotail lobes inferred from spacecraft wake observations
- 2006
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In: Geophysical Research Letters. - : American Geophysical Union. - 0094-8276 .- 1944-8007. ; 33, s. L06110-1-L06110-4
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Journal article (peer-reviewed)abstract
- Cold ionospheric ions with eV energies are common inthe magnetosphere and can travel far out in the magnetotail.However, they are difficult to measure with conventional ionspectrometers mounted on spacecraft, since the potential of asunlit spacecraft often reaches several tens of volts. In thispaper we present two alternative methods of measuring thecold-ion flow with the Cluster spacecraft and apply them onone case in the magnetotail at 18 RE: 1. Ion spectrometer incombination with artificial spacecraft potential control;2. Deriving ion flow velocity (both perpendicular andparallel) from electric field instruments. The secondmethod takes advantage of the effect on the doubleprobeinstrument of the wake formed behind a spacecraftin a plasma flow. The results from the two methods showgood agreement and are also consistent with polar windmodels and previous measurements at lower altitudes,confirming the continuation of low-energy ion outflows.
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| 5. |
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| 6. |
- Roberts, Owen Wyn, et al.
(author)
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Sub-ion Scale Compressive Turbulence in the Solar Wind : MMS Spacecraft Potential Observations
- 2020
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In: Astrophysical Journal Supplement Series. - : American Astronomical Society. - 0067-0049 .- 1538-4365. ; 250:2
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Journal article (peer-reviewed)abstract
- Compressive plasma turbulence is investigated at sub-ion scales in the solar wind using both the Fast Plasma Investigation (FPI) instrument on the Magnetospheric MultiScale mission (MMS), as well as using calibrated spacecraft potential data from the Spin Plane Double Probe (SDP) instrument. The data from FPI allow the sub-ion scale region (f(sc) greater than or similar to 1 Hz) to be investigated before the instrumental noise becomes significant at a spacecraft frame frequency off(sc) 3 Hz. Whereas the calibrated spacecraft potential allows a measurement up tof(sc) 40 Hz. In this work, we give a detailed description of density estimation in the solar wind using the spacecraft potential measurement from the SDP instrument on MMS. Several intervals of solar wind plasma have been processed using the methodology described and are made available. One of the intervals is investigated in more detail and the power spectral density of the compressive fluctuations is measured from the inertial range to the sub-ion range. The morphology of the density spectra can be explained by either a cascade of Alfven waves and slow waves at large scales and kinetic Alfven waves at sub-ion scales or more generally by the Hall effect. Using electric field measurements, the two hypotheses are discussed.
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| 7. |
- Torkar, Klaus, et al.
(author)
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Long-Term Study of Active Spacecraft Potential Control
- 2008
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In: IEEE Transactions on Plasma Science. - 0093-3813 .- 1939-9375. ; 36:5, s. 2294-2300
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Journal article (peer-reviewed)abstract
- Emitters based on the liquid metal ion source principle have been operating on the Cluster spacecraft between 2000 and 2004, in order to control the spacecraft potential. The resulting reduction of positive spacecraft potential reduces perturbations to the plasma measurements on board. Ion currents up to 40 [LA have been applied, which reduced the energy band in which photoelectrons disturb the plasma electron measurements to values close to the lower detection limit of the instrument. The experience with this method, meanwhile, covers both the maximum and minimum of the present solar cycle and allows one to study the variations of photoemission and other long-term trends and their effects on the measurements. A long-term trend of the controlled spacecraft potential is indeed observed. In addition, it appears that reconstruction of the uncontrolled spacecraft potential from the controlled one is possible if certain conditions are fulfilled. Spacecraft potential control can thereby improve the plasma measurements while still allowing one to estimate the total plasma density from the residual potential.
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