| 1. |
- 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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| 2. |
- Fuselier, S. A., et al.
(författare)
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Ion chemistry in the coma of comet 67P near perihelion
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 462, s. S67-S77
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Tidskriftsartikel (refereegranskat)abstract
- The coma and the comet-solar wind interaction of comet 67P/Churyumov-Gerasimenko changed dramatically from the initial Rosetta spacecraft encounter in 2014 August through perihelion in 2015 August. Just before equinox (at 1.6 au from the Sun), the solar wind signal disappeared and two regions of different cometary ion characteristics were observed. These 'outer' and 'inner' regions have cometary ion characteristics similar to outside and inside the ion pileup region observed during the Giotto approach to comet 1P/Halley. Rosetta/Double-Focusing Mass Spectrometer ion mass spectrometer observations are used here to investigate the H3O+/H2O+ ratio in the outer and inner regions at 67P/Churyumov-Gerasimenko. The H3O+/H2O+ ratio and the H3O+ signal are observed to increase in the transition from the outer to the inner region and the H3O+ signal appears to be weakly correlated with cometary ion energy. These ion composition changes are similar to the ones observed during the 1P/Halley flyby. Modelling is used to determine the importance of neutral composition and transport of neutrals and ions away from the nucleus. This modelling demonstrates that changes in the H3O+/H2O+ ratio appear to be driven largely by transport properties and only weakly by neutral composition in the coma.
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| 3. |
- Goetz, C., et al.
(författare)
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Cometary plasma science : Open science questions for future space missions
- 2021
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Ingår i: Experimental astronomy. - : Springer Nature. - 0922-6435 .- 1572-9508.
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Tidskriftsartikel (refereegranskat)abstract
- Comets hold the key to the understanding of our Solar System, its formation and its evolution, and to the fundamental plasma processes at work both in it and beyond it. A comet nucleus emits gas as it is heated by the sunlight. The gas forms the coma, where it is ionised, becomes a plasma, and eventually interacts with the solar wind. Besides these neutral and ionised gases, the coma also contains dust grains, released from the comet nucleus. As a cometary atmosphere develops when the comet travels through the Solar System, large-scale structures, such as the plasma boundaries, develop and disappear, while at planets such large-scale structures are only accessible in their fully grown, quasi-steady state. In situ measurements at comets enable us to learn both how such large-scale structures are formed or reformed and how small-scale processes in the plasma affect the formation and properties of these large scale structures. Furthermore, a comet goes through a wide range of parameter regimes during its life cycle, where either collisional processes, involving neutrals and charged particles, or collisionless processes are at play, and might even compete in complicated transitional regimes. Thus a comet presents a unique opportunity to study this parameter space, from an asteroid-like to a Mars- and Venus-like interaction. The Rosetta mission and previous fast flybys of comets have together made many new discoveries, but the most important breakthroughs in the understanding of cometary plasmas are yet to come. The Comet Interceptor mission will provide a sample of multi-point measurements at a comet, setting the stage for a multi-spacecraft mission to accompany a comet on its journey through the Solar System. This White Paper, submitted in response to the European Space Agency’s Voyage 2050 call, reviews the present-day knowledge of cometary plasmas, discusses the many questions that remain unanswered, and outlines a multi-spacecraft European Space Agency mission to accompany a comet that will answer these questions by combining both multi-spacecraft observations and a rendezvous mission, and at the same time advance our understanding of fundamental plasma physics and its role in planetary systems.
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| 4. |
- Gunell, H., et al.
(författare)
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Ion acoustic waves at comet 67P/Churyumov-Gerasimenko : Observations and computations
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP SCIENCES S A. - 0004-6361 .- 1432-0746. ; 600
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Tidskriftsartikel (refereegranskat)abstract
- Context. On 20 January 2015 the Rosetta spacecraft was at a heliocentric distance of 2.5 AU, accompanying comet 67P/Churyumov-Gerasimenko on its journey toward the Sun. The Ion Composition Analyser (RPC-ICA), other instruments of the Rosetta Plasma Consortium, and the ROSINA instrument made observations relevant to the generation of plasma waves in the cometary environment.Aims. Observations of plasma waves by the Rosetta Plasma Consortium Langmuir probe (RPC-LAP) can be explained by dispersion relations calculated based on measurements of ions by the Rosetta Plasma Consortium Ion Composition Analyser (RPC-ICA), and this gives insight into the relationship between plasma phenomena and the neutral coma, which is observed by the Comet Pressure Sensor of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis instrument (ROSINA-COPS).Methods. We use the simple pole expansion technique to compute dispersion relations for waves on ion timescales based on the observed ion distribution functions. These dispersion relations are then compared to the waves that are observed. Data from the instruments RPC-LAP, RPC-ICA and the mutual impedance probe (RPC-MIP) are compared to find the best estimate of the plasma density.Results. We find that ion acoustic waves are present in the plasma at comet 67P/Churyumov-Gerasimenko, where the major ion species is H2O+. The bulk of the ion distribution is cold, k(B)T(i) = 0.01 eV when the ion acoustic waves are observed. At times when the neutral density is high, ions are heated through acceleration by the solar wind electric field and scattered in collisions with the neutrals. This process heats the ions to about 1 eV, which leads to significant damping of the ion acoustic waves.Conclusions. In conclusion, we show that ion acoustic waves appear in the H2O+ plasmas at comet 67P/Churyumov-Gerasimenko and how the interaction between the neutral and ion populations affects the wave properties.
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| 5. |
- Waara, Martin, 1980-, et al.
(författare)
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Oxygen ion energization observed at high altitudes
- 2010
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Ingår i: Annales Geophysicae. - : Copernicus Publications on behalf of the European Geosciences Union. - 0992-7689 .- 1432-0576. ; 28, s. 907-916
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Tidskriftsartikel (refereegranskat)
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| 6. |
- Waara, M., et al.
(författare)
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Oxygen ion energization observed at high altitudes
- 2010
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 28:4, s. 907-916
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Tidskriftsartikel (refereegranskat)abstract
- We present a case study of significant heating (up to 8 keV) perpendicular to the geomagnetic field of outflowing oxygen ions at high altitude (12 R-E) above the polar cap. The shape of the distribution functions indicates that most of the heating occurs locally (within 0.2-0.4 R-E in altitude). This is a clear example of local ion energization at much higher altitude than usually reported. In contrast to many events at lower altitudes, it is not likely that the locally observed wave fields can cause the observed ion energization. Also, it is not likely that the ions have drifted from some nearby energization region to the point of observation. This suggests that additional fundamentally different ion energization mechanisms are present at high altitudes. One possibility is that the magnetic moment of the ions is not conserved, resulting in slower outflow velocities and longer time for ion energization.
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| 7. |
- Carlsson, Ella, et al.
(författare)
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Analysis of the mass composition of the escaping plasma at Mars
- 2006
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Ingår i: 2006 European Geosciences Union General Assembly (EGU 2006), Austria Center Vienna, Vienna (Austria), 2-7 Apr 2006. - : European Geosciences Union (EGU).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Results from Mars Express, Mars Exploration Rovers and Mars Global Surveyor indicate that Mars harbored large amounts of liquid water on the surface in the past. In order for the water-associated geomorphologic features to form, the pressure in the atmosphere must have been at least a hundred times higher to produce the necessary greenhouse effect required to hold liquid water stable. The present atmospheric pressure is only 6-9 mbar and moreover, the spectral imaging of Mars suggests that the amount of carbonates stored in the surface is too low in order to explain the denser atmosphere in the past. This controversy led us to investigate the escaping plasma by analyzing the data from the IMA sensor (Ion Mass Analyzer) of the ASPERA-3 instrument suite onboard Mars Express. The IMA sensor measures the differential flow of ion components in the energy range of 0.01-30 keV/q.Since the instrument design was optimized for studies of plasma dynamics, the mass resolution is not adequate enough to directly resolve CO+2 from O+2 , which is the main molecular ion composing the Mars ionosphere according to theoretical models. Therefore, a special multi-species fitting technique, using calibration and in-flight data, was developed to resolve the CO+2 peak from the neighboring and much more intense O+2 peak. This technique was applied to the observations covering the period from April 4, 2004 to October 2, 2005. The events of heavy ion escape were identified inside the induced magnetosphere boundary and the Martian eclipse. We report the results of statistical studies of these ion-beam events which permitted to determine CO+2 / O+ and the O+2 / O+ ratio of the escaping plasma at Mars.
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| 8. |
- Gunell, H, et al.
(författare)
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Acceleration of ions and nano dust at a comet in the solar wind
- 2015
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Ingår i: Planetary and Space Science. - : Elsevier. - 0032-0633 .- 1873-5088. ; 119, s. 13-23
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Tidskriftsartikel (refereegranskat)abstract
- A quasi-neutral hybrid simulation of the interaction of the solar wind with the atmosphere of a comet is used together with a test particle simulation of cometary ions and dust to compute trajectories and velocity distribution functions of charged particles, starting outside the diamagnetic cavity at 150 km cometocentric distance. The simulations are run with parameters suited to make predictions for comet 67P/Churyumov-Gerasimenko when it is at a heliocentric distance of 1.45 AU. It is found that the shape of the ion trajectories depends on the location of the source, and that a velocity distribution that is observed at a given point in space is influenced by the spatial structure of the source. Charged dust grains with radii in the 1-10 nm range are accelerated from the nucleus to a distance of 2.9 x 104 km in between 15 min and 2 h approximately. Dust particles smaller than 10 nm in radius are accelerated to speeds over 10 km/s.
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| 9. |
- Gunell, H., et al.
(författare)
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Indications of plasma instabilities near Mars
- 2006
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- It has been suggested in the literature that the Kelvin-Helmholtz instability can be responsible for significant ion loss at Mars through the detachment of ionospheric plasma clouds. Clouds of detached ionospheric plasma were observed at Venus by the Pioneer Venus orbiter. The conditions at Mars differ somewhat from those at Venus. The ratio between the ion gyro radius and the radius of the planet is larger at Mars than at Venus, since Mars is a smaller planet and the solar wind magnetic field is weaker at Mars than at Venus. It is therefore interesting to study instabilities at Mars and to compare the results from Mars with those from Venus. We search the ASPERA-3 data for signatures of instabilities at Mars, in particular looking at the magnetosheath and the induced magnetosphere boundary.
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| 10. |
- Gunell, H., et al.
(författare)
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Numerical experiments on plasmoids entering a transverse magnetic field
- 2009
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Ingår i: Physics of Plasmas. - : AIP Publishing. - 1070-664X .- 1089-7674. ; 16:11
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Tidskriftsartikel (refereegranskat)abstract
- Plasma from the Earth's magnetosheath has previously been observed inside the magnetosphere. Inhomogeneities in the magnetosheath plasma, here called plasmoids, can impact the magnetopause and doing so set up a polarizing field that allows it to penetrate the magnetopause and enter the magnetosphere. A set of simulations of plasmoids with different dimensions is presented in this paper. For plasmoids that are longer than those previously published, waves propagating upstream from the barrier are found. It is also found that the penetration process causes the part of the plasmoid that is upstream of the barrier to rotate. The role of plasmoid width and cross sectional shape in penetration is studied, and for plasmoids that are less than half an ion gyroradius wide, the plasmoid is compressed to obtain a vertically oriented elliptical cross section, regardless of the initial shape. When the initial plasmoid width exceeds the ion gyroradius, the plasmoid still penetrates through a mechanism involving a potential that propagates upstream from the magnetic barrier.
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