| 1. |
- Barabash, S., et al.
(författare)
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Observations of Sounder Accelerated Electrons by Mars Express
- 2020
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 125:1
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Tidskriftsartikel (refereegranskat)abstract
- The electron sensor of the Analyzer of Space Plasmas and Energetic Atoms experiment detects accelerated electrons during pulses of radio emissions from the powerful topside sounder: the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) on board the Mars Express spacecraft. Accelerated electrons are observed at energies up to 400 eV at the times when MARSIS transmits at a frequency between the local plasma frequency and its harmonics (up to 4 times the plasma frequency). When the electron density and magnetic field strength are low (similar to 10(3) cm(-3), similar to 10 nT), the accelerated electrons are almost monoenergetic electron beams. An increase in density and magnetic field (similar to 3 . 10(3) cm(-3), similar to 50 nT) leads to substantial broadening of the energy spectrum of the accelerated electrons. It is concluded that in the latter case, electrons are accelerated by the variable spacecraft potential resulting from the imbalance of the electron and ion currents to the MARSIS antenna during transmission.
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| 2. |
- Broiles, Thomas W., et al.
(författare)
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Statistical analysis of suprathermal electron drivers at 67P/Churyumov-Gerasimenko
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 462, s. S312-S322
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Tidskriftsartikel (refereegranskat)abstract
- We use observations from the Ion and Electron Sensor (IES) on board the Rosetta spacecraft to study the relationship between the cometary suprathermal electrons and the drivers that affect their density and temperature. We fit the IES electron observations with the summation of two kappa distributions, which we characterize as a dense and warm population (similar to 10 cm(-3) and similar to 16 eV) and a rarefied and hot population (similar to 0.01 cm(-3) and similar to 43 eV). The parameters of our fitting technique determine the populations' density, temperature, and invariant kappa index. We focus our analysis on the warm population to determine its origin by comparing the density and temperature with the neutral density and magnetic field strength. We find that the warm electron population is actually two separate sub-populations: electron distributions with temperatures above 8.6 eV and electron distributions with temperatures below 8.6 eV. The two sub-populations have different relationships between their density and temperature. Moreover, the two sub-populations are affected by different drivers. The hotter sub-population temperature is strongly correlated with neutral density, while the cooler sub-population is unaffected by neutral density and is only weakly correlated with magnetic field strength. We suggest that the population with temperatures above 8.6 eV is being heated by lower hybrid waves driven by counterstreaming solar wind protons and newly formed, cometary ions created in localized, dense neutral streams. To the best of our knowledge, this represents the first observations of cometary electrons heated through wave-particle interactions.
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| 3. |
- Carlsson, Ella, et al.
(författare)
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Mass composition of the escaping plasma at Mars
- 2006
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 182:2, s. 320-328
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Tidskriftsartikel (refereegranskat)abstract
- Data from the Ion Mass Analyzer (IMA) sensor of the ASPERA-3 instrument suite on Mars Express have been analyzed to determine the mass composition of the escaping ion species at Mars. We have examined 77 different ion-beam events and we present the results in terms of flux ratios between the following ion species: CO2+/O+ and O-2(+)/O+. The following ratios averaged over all events and energies were identified: CO2+/O+ = 0.2 and O-2(+)/O+ = 0.9. The values measured are significantly higher, by a factor of 10 for O-2(+)/O+, than a contemporary modeled ratio for the maximum fluxes which the martian ionosphere can supply. The most abundant ion species was found to be O+, followed by O-2(+) and CO2+. We estimate the loss of CO2+ to be 4.0 x 10(24) s(-1) (0.29 kg s(-1)) by using the previous measurements of Phobos-2 in our calculations. The dependence of the ion ratios in relation to their energy ranges we studied, 0.3-3.0 keV, indicated that no clear correlation was found.
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| 4. |
- Dieval, Catherine, et al.
(författare)
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A case study of proton precipitation at Mars : Mars Express observations and hybrid simulations
- 2012
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117
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Tidskriftsartikel (refereegranskat)abstract
- Using the data from the Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) experiment on board Mars Express and hybrid simulations, we have investigated the entry of protons into the Martian induced magnetosphere. We discuss one orbit on the dayside with observations of significant proton fluxes at altitudes down to 260 km on 27 February 2004. The protons observed below the induced magnetosphere boundary at an altitude of less than 700 km have energies of a few keV, travel downward, and precipitate onto the atmosphere. The measured energy flux and particle flux are 108–109 eV cm−2 s−1 and 105–106 H+ cm−2 s−1, respectively. The proton precipitation occurs because the Martian magnetosheath is small with respect to the heated proton gyroradius in the subsolar region. The data suggest that the precipitation is not permanent but may occur when there are transient increases in the magnetosheath proton temperature. The higher-energy protons penetrate deeper because of their larger gyroradii. The proton entry into the induced magnetosphere is simulated using a hybrid code. A simulation using a fast solar wind as input can reproduce the high energies of the observed precipitating protons. The model shows that the precipitating protons originate from both the solar wind and the planetary exosphere. The precipitation extends over a few thousand kilometers along the orbit of the spacecraft. The proton precipitation does not necessarily correlate with the crustal magnetic anomalies.
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| 5. |
- Voshchepynets, A., et al.
(författare)
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Ions Accelerated by Sounder-Plasma Interaction as Observed by Mars Express
- 2018
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Ingår i: Journal of Geophysical Research - Space Physics. - : AMER GEOPHYSICAL UNION. - 2169-9380 .- 2169-9402. ; 123:11, s. 9802-9814
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Tidskriftsartikel (refereegranskat)abstract
- The ion sensor of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) experiment detects accelerated ions during pulses of radio emissions from the powerful topside sounder: the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) onboard Mars Express. Accelerated ions (O-2(+), O+, and lighter ions) are observed in an energy range up to 800 eV when MARSIS transmits at a frequency close to the plasma frequency. Individual observations consist of almost monoenergetic ion beams aligned with the MARSIS antenna or lying in the plane perpendicular to the antenna. The observed ion beams are often accompanied by a small decrease in the electron flux observed by the electron sensor of Analyzer of Space Plasmas and Energetic Atoms 3. Observations indicate that the voltage applied to the antenna causes charging of the spacecraft to several hundreds of volts by the electrons of the ambient plasma. Positively charged ions are accelerated when the spacecraft discharges.
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