| 1. |
- Huybrighs, H. L. F., et al.
(författare)
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An Active Plume Eruption on Europa During Galileo Flyby E26 as Indicated by Energetic Proton Depletions
- 2020
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 47:10
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Tidskriftsartikel (refereegranskat)abstract
- Strong depletions of energetic protons (115-244 keV) were observed during Galileo flyby E26 of Europa. We simulate the flux of energetic protons using a Monte Carlo particle backtracing code and show that energetic proton depletions during E26 are reproduced by taking into account the perturbations of the electromagnetic fields calculated by magnetohydrodynamic (MHD) simulations and charge exchange with a global atmosphere and plume. A depletion feature occurring shortly after closest approach is driven by plume associated charge exchange, or a combination with plume associated field perturbations. We therefore conclude, with a new method and independent data set, that Galileo could have encountered a plume during E26.
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| 2. |
- Opgenoorth, Hermann J., et al.
(författare)
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Mars ionospheric response to solar wind variability
- 2013
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Ingår i: Journal of Geophysical Research: Space Physics. - : American Geophysical Union (AGU). - 2169-9380. ; 118:10, s. 6558-6587
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Tidskriftsartikel (refereegranskat)abstract
- At planets with induced magnetospheres, the coupling between the ionosphere, the weak draped magnetosphere, and the solar wind is very direct in comparison to Earth. The weak induced magnetosphere itself is created by the prevailing Solar wind conditions and therefore in its shape and strength dynamically depending on it. In early 2010, Mars was located behind Earth in the Solar wind; thus, we can use coordinated data from multiple near-Earth spacecraft (Stereo, Wind) to evaluate what kind of Solar wind disturbances have passed by Earth and might consecutively hit Mars, and when. We employ plasma data from the ESA Mars-Express mission, the ASPERA-3 particle instrument, and the MARSIS Active Ionospheric Sounder (AIS) to investigate, for a number of isolated events in March and April 2010, how the ionosphere and the induced magnetosphere at Mars develop and decay in response to Solar wind variability in the magnetic field, density, and velocity. In a dedicated campaign mode, we use frequent long-duration MARSIS AIS operations for several consecutive orbits, to monitor for the first time the long-term development of the Martian plasma environment during solar wind disturbances. We find that the magnetosphere and ionosphere of Mars can become considerably compressed by solar wind dynamic pressure variations, which usually are also associated with changes in the magnetic draping of the interplanetary magnetic field around the planet. These are typically associated with corotating interaction regions and coronal mass ejections, and can last for several days. During such episodes of compression, we see signatures of increased plasma transport over the terminator and enhanced ion outflow from the upper atmosphere.
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| 3. |
- Stephan, K., et al.
(författare)
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Regions of interest on Ganymede's and Callisto's surfaces as potential targets for ESA's JUICE mission
- 2021
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Ingår i: Planetary and Space Science. - : Elsevier. - 0032-0633 .- 1873-5088. ; 208
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Tidskriftsartikel (refereegranskat)abstract
- The JUpiter Icy moons Explorer (JUICE) will investigate Ganymede's and Callisto's surfaces and subsurfaces from orbit to explore the geologic processes that have shaped and altered their surfaces by impact, tectonics, possible cryovolcanism, space weathering due to micrometeorites, radiation and charged particles as well as explore the structure and properties of the icy crust and liquid shell (Grasset et al., 2013). The best possible synergy of the JUICE instruments is required to answer the major science objective of this mission and to fully exploit the po-tential of the JUICE mission. Therefore, the JUICE team is aiming to define high priority targets on both Gany-mede's and Callisto's surfaces to support the coordination of the planning activities by the individual instrument teams. Based on the science objectives of the JUICE mission and the most recent knowledge of Ganymede's and Callisto's geologic evolution we propose a collection of Regions of Interest (RoIs), which characterize surface features and terrain types representing important traces of geologic processes, from past and/or present cryovolcanic and tectonic activity to space weathering processes, which are crucial to understand the geologic evolution of Ganymede and Callisto. The proposed evaluation of RoIs is based on their scientific importance as well as on the opportunities and conditions to observe them during the currently discussed mission profile.
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| 4. |
- Andrews, David J., et al.
(författare)
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Determination of local plasma densities with the MARSIS radar : Asymmetries in the high-altitude Martian ionosphere
- 2013
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Ingår i: Journal of Geophysical Research: Space Physics. - : American Geophysical Union (AGU). - 2169-9380. ; 118:10, s. 6228-6242
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Tidskriftsartikel (refereegranskat)abstract
- We present a novel method for the automatic retrieval of local plasma density measurements from the Mars advanced radar for subsurface and ionospheric sounding (MARSIS) active ionospheric sounder (AIS) instrument. The resulting large data set is then used to study the configuration of the Martian ionosphere at altitudes above approximate to 300km. An empirical calibration routine is used, which relates the local plasma density to the measured intensity of multiple harmonics of the local plasma frequency oscillation, excited in the plasma surrounding the antenna in response to the transmission of ionospheric sounding pulses. Enhanced accuracy is achieved in higherdensity (n(e)>150cm(-3)) plasmas, when MARSIS AIS is able to directly measure the fundamental frequency of the local plasma oscillation. To demonstrate the usefulness of this data set, the derived plasma densities are binned by altitude and solar zenith angle in regions over weak (|B-c|<20nT) and strong (|B-c|>20nT) crustal magnetic fields, and we find clear and consistent evidence for a significant asymmetry between these two regions. We show that within the approximate to 300-1200km altitude range sampled, the median plasma density is substantially higher on the dayside in regions of relatively stronger crustal fields than under equivalent illuminations in regions of relatively weaker crustal fields. Conversely, on the nightside, median plasma densities are found to be higher in regions of relatively weaker crustal fields. We suggest that the observed asymmetry arises as a result of the modulation of the efficiency of plasma transport processes by the irregular crustal fields and the generally horizontal draped interplanetary magnetic field.
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| 5. |
- Andrews, David J., et al.
(författare)
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Oblique reflections in the Mars Express MARSIS data set : Stable density structures in the Martian ionosphere
- 2014
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Ingår i: Journal of Geophysical Research-Space Physics. - 2169-9380. ; 119:5, s. 3944-3960
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Tidskriftsartikel (refereegranskat)abstract
- The Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) onboard the European Space Agency's Mars Express (MEX) spacecraft routinely detects evidence of localized plasma density structures in the Martian dayside ionosphere. Such structures, likely taking the form of spatially extended elevations in the plasma density at a given altitude, give rise to oblique reflections in the Active Ionospheric Sounder data. These structures are likely related to the highly varied Martian crustal magnetic field. In this study we use the polar orbit of MEX to investigate the repeatability of the ionospheric structures producing these anomalous reflections, examining data taken in sequences of multiple orbits which pass over the same regions of the Martian surface under similar solar illuminations, within intervals lasting tens of days. Presenting three such examples, or case studies, we show for the first time that these oblique reflections are often incredibly stable, indicating that the underlying ionospheric structures are reliably reformed in the same locations and with qualitatively similar parameters. The visibility, or lack thereof, of a given oblique reflection on a single orbit can generally be attributed to variations in the crustal field within the ionosphere along the spacecraft trajectory. We show that, within these examples, oblique reflections are generally detected whenever the spacecraft passes over regions of intense near-radial crustal magnetic fields (i.e., with a cusp-like configuration). The apparent stability of these structures is an important feature that must be accounted for in models of their origin.
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| 6. |
- Andrews, David J., et al.
(författare)
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Plasma observations during the Mars atmospheric "plume" event of March-April 2012
- 2016
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 121:4, s. 3139-3154
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Tidskriftsartikel (refereegranskat)abstract
- We present initial analyses and conclusions from plasma observations made during the reported "Mars plume event" of March-April 2012. During this period, multiple independent amateur observers detected a localized, high-altitude "plume" over the Martian dawn terminator, the cause of which remains to be explained. The estimated brightness of the plume exceeds that expected for auroral emissions, and its projected altitude greatly exceeds that at which clouds are expected to form. We report on in situ measurements of ionospheric plasma density and solar wind parameters throughout this interval made by Mars Express, obtained over the same surface region but at the opposing terminator. Measurements in the ionosphere at the corresponding location frequently show a disturbed structure, though this is not atypical for such regions with intense crustal magnetic fields. We tentatively conclude that the formation and/or transport of this plume to the altitudes where it was observed could be due in part to the result of a large interplanetary coronal mass ejection (ICME) encountering the Martian system. Interestingly, we note that the only similar plume detection in May 1997 may also have been associated with a large ICME impact at Mars.
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| 7. |
- Duev, Dmitry, et al.
(författare)
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Planetary Radio Interferometry and Doppler Experiment (PRIDE) technique: A test case of the Mars Express Phobos fly-by
- 2016
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 593:A34
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Tidskriftsartikel (refereegranskat)abstract
- The closest ever fly-by of the Martian moon Phobos, performed by the European Space Agency's Mars Express spacecraft, gives a unique opportunity to sharpen and test the Planetary Radio Interferometry and Doppler Experiments (PRIDE) technique in the interest of studying planet-satellite systems. Aims. The aim of this work is to demonstrate a technique of providing high precision positional and Doppler measurements of planetary spacecraft using the Mars Express spacecraft. The technique will be used in the framework of Planetary Radio Interferometry and Doppler Experiments in various planetary missions, in particular in fly-by mode. Methods. We advanced a novel approach to spacecraft data processing using the techniques of Doppler and phase-referenced very long baseline interferometry spacecraft tracking. Results. We achieved, on average, mHz precision (30 mu m/s at a 10 s integration time) for radial three-way Doppler estimates and sub-nanoradian precision for lateral position measurements, which in a linear measure (at a distance of 1.4 AU) corresponds to similar to 50 m.
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| 8. |
- Hall, B. E. S., et al.
(författare)
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Annual variations in the Martian bow shock location as observed by the Mars Express mission
- 2016
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 121:11, s. 11474-11494
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Tidskriftsartikel (refereegranskat)abstract
- The Martian bow shock distance has previously been shown to be anticorrelated with solar wind dynamic pressure but correlated with solar extreme ultraviolet (EUV) irradiance. Since both of these solar parameters reduce with the square of the distance from the Sun, and Mars' orbit about the Sun increases by similar to 0.3 AU from perihelion to aphelion, it is not clear how the bow shock location will respond to variations in these solar parameters, if at all, throughout its orbit. In order to characterize such a response, we use more than 5 Martian years of Mars Express Analyser of Space Plasma and EneRgetic Atoms (ASPERA-3) Electron Spectrometer measurements to automatically identify 11,861 bow shock crossings. We have discovered that the bow shock distance as a function of solar longitude has a minimum of 2.39 R-M around aphelion and proceeds to a maximum of 2.65 R-M around perihelion, presenting an overall variation of similar to 11% throughout the Martian orbit. We have verified previous findings that the bow shock in southern hemisphere is on average located farther away from Mars than in the northern hemisphere. However, this hemispherical asymmetry is small (total distance variation of similar to 2.4%), and the same annual variations occur irrespective of the hemisphere. We have identified that the bow shock location is more sensitive to variations in the solar EUV irradiance than to solar wind dynamic pressure variations. We have proposed possible interaction mechanisms between the solar EUV flux and Martian plasma environment that could explain this annual variation in bow shock location.
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| 9. |
- Huybrighs, H. L.F., et al.
(författare)
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Europa's Perturbed Fields and Induced Dipole Affect Energetic Proton Depletions During Distant Alfvén Wing Flybys
- 2023
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 128:9
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the causes of energetic proton (80–540 keV) depletions measured during the two most distant flybys of Europa by Galileo, E17 and E25A, which encountered the Alfvén wings. First, by simulating the proton flux with a Monte Carlo particle tracing code we investigate the effect of: electromagnetic field perturbations, the induced dipole, atmospheric charge exchange and plumes. Inhomogeneous fields associated with the Alfvén wings and the ionosphere strongly affect the depletions. For homogeneous fields the depletion along the trajectory is focused on a narrow pitch angle range and has no structure, whereas the depletion for perturbed (inhomogeneous) fields represents a wider and complex structure. Furthermore, also the induced dipole alters the depletion structure. The effect of plumes (density 2.5 × 1015 m−3) and charge exchange on the proton depletion is minor. Second, we compare the simulations to the proton measurements. The simulations with inhomogeneous fields describe the data qualitatively better than the homogeneous case, suggesting that indeed field perturbations are responsible for the measured losses. We attribute discrepancies between the simulations and the proton measurements to discrepancies between the simulated and real fields. We argue that simulating the fields along the trajectory is a good first step, but that ideally the energetic ion flux is reconstructed well to gain confidence in the interpretation of the simulated magnetic field. In conclusion, energetic ion observations along distant flybys through the Alfvén wings are suitable for isolating the characteristics of the global configuration of the magnetospheric interaction region of Europa (or other moons).
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| 10. |
- Huybrighs, H. L. F., et al.
(författare)
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Reply to Comment on "An Active Plume Eruption on Europa During Galileo Flyby E26 as Indicated by Energetic Proton Depletions"
- 2021
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Ingår i: Geophysical Research Letters. - : American Geophysical Union (AGU). - 0094-8276 .- 1944-8007. ; 48:18
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Tidskriftsartikel (refereegranskat)abstract
- In Huybrighs et al. (2020, https://doi.org/10.1029/2020gl087806) we investigated energetic proton depletions along Galileo's Europa flyby E26. Based on a particle tracing analysis, we proposed that depletions are caused by perturbed electromagnetic fields combined with atmospheric charge exchange and possible plumes. One depletion feature identified as a plume signature was shown to be an artifact (Jia et al., 2021, https://doi.org/10.1029/2020gl091550). Despite that, here we emphasize that Huybrighs et al. (2020, https://doi.org/10.1029/2020gl087806) demonstrates that plumes can cause proton depletions and that these features should be sought after. Furthermore, the conclusions on the importance of perturbed electromagnetic fields and atmospheric charge exchange on the depletions are unaffected. We suggest that the artifact's cause is a mistagging of protons as heavier ions by EPD. The artifact prevents us from confirming or excluding that there is a plume-associated depletion. We also address comments on the MHD simulations and demonstrate that 540-1,040 keV losses are not necessarily inconsistent with 115-244 keV losses by plume-associated charge exchange. Plain Language Summary In Huybrighs et al. (2020, https://doi.org/10.1029/2020gl087806) we identified why fast protons were disappearing during Europa flyby E26 by Galileo. Beyond impacting on the surface, we identified several contributing factors: First, perturbed electromagnetic fields resulting from the interaction of Europa's atmosphere with the magnetospheric plasma, which deflect the protons. Second, atmospheric charge exchange. We also showed that a water plume eruption could cause a region in which disappearances occur due to a combination of charge exchange and magnetic deflections. We identified a 20s decrease of protons as evidence of such a plume. However, an artifact in the data reported by Jia et al. (2021, https://doi.org/10.1029/2020gl091550) coincides with this 20s moment and prevents us from reaching a conclusion on the occurrence of a plume-associated depletion. We emphasize that our conclusions on the importance of perturbed fields and charge exchange are unaffected, as the artifact only affects a short segment of the data we analyzed. Furthermore, our results demonstrate that plumes can cause proton depletions and that these features should be sought after in the data.
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