| 1. |
- Farrell, William M., et al.
(författare)
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The dust, atmosphere, and plasma at the moon
- 2024
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Ingår i: Reviews in Mineralogy and Geochemistry, Mineralogical Society of America. - : Walter de Gruyter. - 1529-6466 .- 1943-2666. ; 89, s. 563-609
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Fatemi, Shahab, et al.
(författare)
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Effects of protons deflected by lunar crustal magnetic fields on the global lunar plasma environment
- 2014
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Ingår i: Journal of Geophysical Research - Space Physics. - : John Wiley & Sons. - 2169-9380 .- 2169-9402. ; 119:8, s. 6095-6105
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Tidskriftsartikel (refereegranskat)abstract
- Solar wind plasma interaction with lunar crustal magnetic fields is different than that of magnetized bodies like the Earth. Lunar crustal fields are, for typical solar wind conditions, not strong enough to form a (bow)shock upstream but rather deflect and perturb plasma and fields. Here we study the global effects of protons reflected from lunar crustal magnetic fields on the lunar plasma environment when the Moon is in the unperturbed solar wind. We employ a three-dimensional hybrid model of plasma and an observed map of reflected protons from lunar magnetic anomalies over the lunar farside. We observe that magnetic fields and plasma upstream over the lunar crustal fields compress to nearly 120% and 160% of the solar wind, respectively. We find that these disturbances convect downstream in the vicinity of the lunar wake, while their relative magnitudes decrease. In addition, solar wind protons are disturbed and heated at compression regions and their velocity distribution changes from Maxwellian to a non-Maxwellian. Finally, we show that these features persists, independent of the details of the ion reflection by the magnetic fields.
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| 3. |
- Fatemi, Shahab, et al.
(författare)
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The effects of lunar surface plasma absorption and solar wind temperature anisotropies on the solar wind proton velocity space distributions in the low-altitude lunar plasma wake
- 2012
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 117:10
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Tidskriftsartikel (refereegranskat)abstract
- We study the solar wind proton velocity space distribution functions on the lunar nightside at low altitudes (∼100 km) above the lunar surface using a three-dimensional hybrid plasma solver, when the Moon is in the unperturbed solar wind. When the solar wind encounters a passive obstacle, such as the Moon, without any strong magnetic field and no atmosphere, solar wind protons that impact the obstacle's surface are absorbed and removed from the velocity space distribution functions. We show first that a hybrid model of plasma is applicable to study the low-altitude lunar plasma wake by comparing the simulation results with observations. Then we examine the effects of a solar wind bi-Maxwellian velocity space distribution function and the lunar surface plasma absorption on the solar wind protons' velocity space distribution functions and their entry in the direction parallel to the interplanetary magnetic field lines into the low-altitude lunar wake. We present a backward Liouville method for particle-in-cell solvers that improves velocity space resolution. The results show that the lunar surface plasma absorption and anisotropic solar wind velocity space distributions result in substantial changes in the solar wind proton distribution functions in the low-altitude lunar plasma wake, modifying proton number density, velocity, and temperature there. Additionally, a large temperature anisotropy is found at close distances to the Moon on the lunar nightside as a consequence of the lunar surface plasma absorption effect
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| 4. |
- Fatemi, Shahab, et al.
(författare)
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The lunar wake current systems
- 2013
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 40:1, s. 17-21
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Tidskriftsartikel (refereegranskat)abstract
- We present the lunar wake current systems when the Moon is assumed to be a non-conductive body, absorbing the solar wind plasma. We show that in the transition regions between the plasma void, the expanding rarefaction region, and the interplanetary plasma, there are three main currents flowing around these regions in the lunar wake. The generated currents induce magnetic fields within these regions and perturb the field lines there. We use a three-dimensional, self-consistent hybrid model of plasma (particle ions and fluid electrons) to show the flow of these three currents. First, we identify the different plasma regions, separated by the currents, and then we show how the currents depend on the interplanetary magnetic field direction. Finally, we discuss the current closures in the lunar wake.
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| 5. |
- Galli, André, et al.
(författare)
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The tailward flow of energetic neutral atoms observed at Mars
- 2008
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Ingår i: Journal of Geophysical Research. - Washington : American Geophysical Union (AGU). - 0148-0227 .- 2156-2202. ; 113
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Tidskriftsartikel (refereegranskat)abstract
- The ASPERA-3 experiment on Mars Express provides the first measurements of energetic neutral atoms (ENAs) from Mars. These measurements are used to study the global structure of the interaction of the solar wind with the Martian atmosphere. In this study we describe the tailward ENA flow observed at the nightside of Mars. After characterizing energy spectra of hydrogen ENA signals, we present composite images of the ENA intensities and compare them to theoretical predictions (empirical and MHD models). We find that the tailward flow of hydrogen ENAs is mainly generated by shocked solar wind protons. Despite intensive search, no oxygen ENAs above the instrument threshold are detected. The results challenge existing plasma models and constrain the hydrogen exospheric densities and atmospheric hydrogen and oxygen loss rates at low solar activity.
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| 6. |
- Holmström, Mats, et al.
(författare)
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The interaction between the Moon and the solar wind
- 2012
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Ingår i: Earth Planets and Space. - : Springer Science and Business Media LLC. - 1343-8832 .- 1880-5981. ; 64:2, s. 237-245
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Tidskriftsartikel (refereegranskat)abstract
- We study the interaction between the Moon and the solar wind using a three-dimensional hybrid plasma solver. The proton fluxes and electromagnetical fields are presented for typical solar wind conditions with different magnetic field directions. We find two different wake structures for an interplanetary magnetic field that is perpendicular to the solar wind flow, and for one that is parallell to the flow. The wake for intermediate magnetic field directions will be a mix of these two extreme conditions. Several features are consistent with a fluid interaction, e.g., the presence of a rarefaction cone, and an increased magnetic field in the wake. There are however several kinetic features of the interaction. We find kinks in the magnetic field at the wake boundary. There are also density and magnetic field variations in the far wake, maybe from an ion beam instability related to the wake refill. The results are compared to observations by the WIND spacecraft during a wake crossing. The model magnetic field and ion velocities are in agreement with the measurements. The density and the electron temperature in the central wake are not as well captured by the model, probably from the lack of electron physics in the hybrid model.
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| 7. |
- Lue, Charles, et al.
(författare)
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Strong influence of lunar crustal fields on the solar wind flow
- 2011
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 38:3
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Tidskriftsartikel (refereegranskat)abstract
- We discuss the influence of lunar magnetic anomalies on the solar wind and on the lunar surface, based on maps of solar wind proton fluxes deflected by the magnetic anomalies. The maps are produced using data from the Solar WInd Monitor (SWIM) onboard the Chandrayaan-1 spacecraft. We find a high deflection efficiency (average ∼10%, locally ∼50%) over the large-scale (>1000 km) regions of magnetic anomalies. Deflections are also detected over weak (<3 nT at 30 km altitude) and small-scale (<100 km) magnetic anomalies, which might be explained by charge separation and the resulting electric potential. Strong deflection from a wide area implies that the magnetic anomalies act as a magnetosphere-like obstacle, affecting the upstream solar wind. It also reduces the implantation rate of the solar wind protons to the lunar surface, which may affect space weathering near the magnetic anomalies.
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| 8. |
- Nilsson, Hans, et al.
(författare)
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Heavy ion escape from Mars, influence from solar wind conditions and crustal magnetic fields
- 2011
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Ingår i: Icarus. - : Elsevier BV. - 0019-1035 .- 1090-2643. ; 215:2, s. 475-484
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Tidskriftsartikel (refereegranskat)abstract
- We have used more than 4 years of Mars Express ion data to estimate the escape of heavy ions (O(1)(+) O(2)(+) and CO(2)(+)) from Mars. To take the limited field of view of the instrument into account, the data has been binned into spatial bins and angular bins to create average distribution functions for different positions in the near Mars space. The net escape flux for the studied low solar activity period, between May 2007 and May 2011, is 2.0 +/- 0.2 x 10(24) s(-1). The escape has been calculated independently for four different quadrants in the Y(MSO) - Zmso plane, south, dusk, north and dawn. Escape is highest from the northern and dusk quadrants, 0.6 +/- 0.1 x 10(24) s(-1), and smallest from the south and dawn quadrants, 0.4 +/- 0.1 x 10(24) s(-1). The flux ratio of molecular (O(2)(+) and CO(2)())(+) to 0 ions is 0.9 +/- 0.1, averaged over all quadrants. The flux difference between the north and south quadrants is statistically significant, and is presumed to be due to the presence of significant crustal magnetic fields in the southern hemisphere, reducing the outflow. The difference between the dawn and dusk quadrants is likely due to the magnetic tension associated with the nominal Parker angle spiral, which should lead to higher average magnetic tension on the dusk side. The escape increases during periods of high solar wind flux and during times when co-rotating interaction regions (CIR) affect Mars. In the latter case the increase is a factor 2.4-2.9 as compared to average conditions.
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| 9. |
- Nilsson, Hans, et al.
(författare)
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Solar cycle variation of ion escape from Mars
- 2023
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Ingår i: Icarus. - : Academic Press. - 0019-1035 .- 1090-2643. ; 393
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Tidskriftsartikel (refereegranskat)abstract
- Using Mars Express data from 2007 until 2020 we show how ion outflow from Mars varied over more than a solar cycle, from one solar minimum to another. The data was divided into intervals with a length of one Martian year, starting from 30 April 2007 and ending 13 July 2020. The net escape rate was about 5×1024s−1 in the first covered minimum, and 2−3×1024s−1 in the most recent minimum. Ion escape peaked at 1×1025s−1 during the intervening solar maximum. The outflow is a clear function of the solar cycle, in agreement with previous studies which found a clear relationship between solar EUV flux and ion escape at Mars. The outflow during solar maximum is 2.5 to 3 times higher than in the surrounding solar minima. The average solar wind dynamic pressure over a Martian year was investigated, but does not vary much with the solar cycle. The escape rate at solar maximum is in good agreement with some recent MAVEN studies, and dominated by low energy ions at most sampled locations. A simple linear fit to the data gives a prediction of the escape rate for the much stronger solar maximum during the Phobos mission in 1989 that is consistent with observations. The fit also implies a non-linear response of ion escape for low solar EUV, with a lower initial escape response for lower solar EUV levels than those of the studied data set.
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| 10. |
- Nilsson, Hans, et al.
(författare)
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Upstream solar wind speed at comet 67P : reconstruction method, model comparison, and results
- 2022
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 659
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Tidskriftsartikel (refereegranskat)abstract
- Context: Rosetta followed comet 67P at heliocentric distances from 1.25 to 3.6 au. The solar wind was observed for much of this time, but was significantly deflected and to some extent slowed down by the interaction with the coma.Aims: We use the different changes in the speed of H+ and He2+ when they interact with the coma to estimate the upstream speed of the solar wind. The different changes in the speed are due to the different mass per charge of the particles, while the electric force per charge due to the interaction is the same. A major assumption is that the speeds of H+ and He2+ were the same in the upstream region. This is investigated.Methods: We derived a method for reconstructing the upstream solar wind from H+ and He2+ observations. The method is based on the assumption that the interaction of the comet with the solar wind can be described by an electric potential that is the same for both H+ and He2+. This is compared to estimates from the Tao model and to OMNI and Mars Express data that we propagated to the observation point.Results: The reconstruction agrees well with the Tao model for most of the observations, in particular for the statistical distribution of the solar wind speed. The electrostatic potential relative to the upstream solar wind is derived and shows values from a few dozen volts at large heliocentric distances to about 1 kV during solar events and close to perihelion. The reconstructed values of the solar wind for periods of high electrostatic potential also agree well with propagated observations and model results.Conclusions: The reconstructed upstream solar wind speed during the Rosetta mission agrees well with the Tao model. The Tao model captures some slowing down of high-speed streams as compared to observations at Earth or Mars. At low solar wind speeds, below 400 km s-1, the agreement is better between our reconstruction and Mars observations than with the Tao model. The magnitude of the reconstructed electrostatic potential is a good measure of the slowing-down of the solar wind at the observation point.
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