| 1. |
- Coustenis, A., et al.
(författare)
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TandEM : Titan and Enceladus mission
- 2009
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Ingår i: Experimental astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 23:3, s. 893-946
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Tidskriftsartikel (refereegranskat)abstract
- TandEM was proposed as an L-class (large) mission in response to ESA's Cosmic Vision 2015-2025 Call, and accepted for further studies, with the goal of exploring Titan and Enceladus. The mission concept is to perform in situ investigations of two worlds tied together by location and properties, whose remarkable natures have been partly revealed by the ongoing Cassini-Huygens mission. These bodies still hold mysteries requiring a complete exploration using a variety of vehicles and instruments. TandEM is an ambitious mission because its targets are two of the most exciting and challenging bodies in the Solar System. It is designed to build on but exceed the scientific and technological accomplishments of the Cassini-Huygens mission, exploring Titan and Enceladus in ways that are not currently possible (full close-up and in situ coverage over long periods of time). In the current mission architecture, TandEM proposes to deliver two medium-sized spacecraft to the Saturnian system. One spacecraft would be an orbiter with a large host of instruments which would perform several Enceladus flybys and deliver penetrators to its surface before going into a dedicated orbit around Titan alone, while the other spacecraft would carry the Titan in situ investigation components, i.e. a hot-air balloon (MontgolfiSre) and possibly several landing probes to be delivered through the atmosphere.
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| 2. |
- Yamauchi, M., et al.
(författare)
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Plasma-neutral gas interactions in various space environments : Assessment beyond simplified approximations as a Voyage 2050 theme
- 2022
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Ingår i: Experimental astronomy. - : Springer Nature. - 0922-6435 .- 1572-9508.
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Tidskriftsartikel (refereegranskat)abstract
- In the White Paper, submitted in response to the European Space Agency (ESA) Voyage 2050 Call, we present the importance of advancing our knowledge of plasma-neutral gas interactions, and of deepening our understanding of the partially ionized environments that are ubiquitous in the upper atmospheres of planets and moons, and elsewhere in space. In future space missions, the above task requires addressing the following fundamental questions: (A) How and by how much do plasma-neutral gas interactions influence the re-distribution of externally provided energy to the composing species? (B) How and by how much do plasma-neutral gas interactions contribute toward the growth of heavy complex molecules and biomolecules? Answering these questions is an absolute prerequisite for addressing the long-standing questions of atmospheric escape, the origin of biomolecules, and their role in the evolution of planets, moons, or comets, under the influence of energy sources in the form of electromagnetic and corpuscular radiation, because low-energy ion-neutral cross-sections in space cannot be reproduced quantitatively in laboratories for conditions of satisfying, particularly, (1) low-temperatures, (2) tenuous or strong gradients or layered media, and (3) in low-gravity plasma. Measurements with a minimum core instrument package (< 15 kg) can be used to perform such investigations in many different conditions and should be included in all deep-space missions. These investigations, if specific ranges of background parameters are considered, can also be pursued for Earth, Mars, and Venus.
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| 3. |
- Orsini, S., et al.
(författare)
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Inner southern magnetosphere observation of Mercury via SERENA ion sensors in BepiColombo mission
- 2022
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Ingår i: Nature Communications. - : Nature Publishing Group. - 2041-1723. ; 13:1
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Tidskriftsartikel (refereegranskat)abstract
- Mercury’s southern inner magnetosphere is an unexplored region as it was not observed by earlier space missions. In October 2021, BepiColombo mission has passed through this region during its first Mercury flyby. Here, we describe the observations of SERENA ion sensors nearby and inside Mercury’s magnetosphere. An intermittent high-energy signal, possibly due to an interplanetary magnetic flux rope, has been observed downstream Mercury, together with low energy solar wind. Low energy ions, possibly due to satellite outgassing, were detected outside the magnetosphere. The dayside magnetopause and bow-shock crossing were much closer to the planet than expected, signature of a highly eroded magnetosphere. Different ion populations have been observed inside the magnetosphere, like low latitude boundary layer at magnetopause inbound and partial ring current at dawn close to the planet. These observations are important for understanding the weak magnetosphere behavior so close to the Sun, revealing details never reached before.
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| 4. |
- Plainaki, C., et al.
(författare)
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Towards a Global Unified Model of Europa’s Tenuous Atmosphere
- 2018
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Ingår i: Space Science Reviews. - : Springer Netherlands. - 0038-6308 .- 1572-9672. ; 214:1
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Forskningsöversikt (refereegranskat)abstract
- Despite the numerous modeling efforts of the past, our knowledge on the radiation-induced physical and chemical processes in Europa’s tenuous atmosphere and on the exchange of material between the moon’s surface and Jupiter’s magnetosphere remains limited. In lack of an adequate number of in situ observations, the existence of a wide variety of models based on different scenarios and considerations has resulted in a fragmentary understanding of the interactions of the magnetospheric ion population with both the moon’s icy surface and neutral gas envelope. Models show large discrepancy in the source and loss rates of the different constituents as well as in the determination of the spatial distribution of the atmosphere and its variation with time. The existence of several models based on very different approaches highlights the need of a detailed comparison among them with the final goal of developing a unified model of Europa’s tenuous atmosphere. The availability to the science community of such a model could be of particular interest in view of the planning of the future mission observations (e.g., ESA’s JUpiter ICy moons Explorer (JUICE) mission, and NASA’s Europa Clipper mission). We review the existing models of Europa’s tenuous atmosphere and discuss each of their derived characteristics of the neutral environment. We also discuss discrepancies among different models and the assumptions of the plasma environment in the vicinity of Europa. A summary of the existing observations of both the neutral and the plasma environments at Europa is also presented. The characteristics of a global unified model of the tenuous atmosphere are, then, discussed. Finally, we identify needed future experimental work in laboratories and propose some suitable observation strategies for upcoming missions.
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| 5. |
- Runov, A., et al.
(författare)
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Observations of an active thin current sheet
- 2008
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 113:A7
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Tidskriftsartikel (refereegranskat)abstract
- We analyze observations of magnetotail current sheet dynamics during a substorm between 2330 and 2400 UT on 28 August 2005 when Cluster was in the plasma sheet at [-17.2, -4.49, 0.03] R-E (GSM) with the foot points near the IMAGE ground-based network. Observations from the Cluster spacecraft, ground-based magnetometers, and the IMAGE satellite showed that the substorm started in a localized region near midnight, expanding azimuthally. A thin current sheet with a thickness of less than 900 km and current density of about 30 nA/m(2) was observed during 5 min around the substorm onset. The thinning of the current sheet was accompanied by tailward plasma flow at a velocity of -700 km/s and subsequent reversal to earthward flow at V-x approximate to 500 km/s coinciding with a B-z turning from -5 to + 10 nT. The analysis of magnetic and electric fields behavior and particle distributions reveals signatures of impulsive (with similar to 1 min timescale) activations of the thin current sheet. These observations were interpreted in the framework of transient reconnection, although the data analysis reveals serious disagreements with the classical 2.5-D X line model.
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| 6. |
- Aikio, A. T., et al.
(författare)
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EISCAT and Cluster observations in the vicinity of the dynamical polar cap boundary
- 2008
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Ingår i: Annales Geophysicae. - : Copernicus GmbH. - 0992-7689 .- 1432-0576. ; 26:1, s. 87-105
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Tidskriftsartikel (refereegranskat)abstract
- The dynamics of the polar cap boundary and auroral oval in the nightside ionosphere are studied during late expansion and recovery of a substorm from the region between Tromso (66.6 degrees cgmLat) and Longyearbyen (75.2 degrees cgmLat) on 27 February 2004 by using the coordinated EISCAT incoherent scatter radar, MIRACLE magnetometer and Cluster satellite measurements. During the late substorm expansion/early recovery phase, the polar cap boundary (PCB) made zig-zag-type motion with amplitude of 2.5 degrees cgmLat and period of about 30 min near magnetic midnight. We suggest that the poleward motions of the PCB were produced by bursts of enhanced reconnection at the near-Earth neutral line (NENL). The subsequent equatorward motions of the PCB would then represent the recovery of the merging line towards the equilibrium state (Cowley and Lockwood, 1992). The observed bursts of enhanced westward electrojet just equatorward of the polar cap boundary during poleward expansions were produced plausibly by particles accelerated in the vicinity of the neutral line and thus lend evidence to the Cowley-Lockwood paradigm. During the substorm recovery phase, the footpoints of the Cluster satellites at a geocentric distance of 4.4 R-E mapped in the vicinity of EISCAT measurements. Cluster data indicate that outflow of H+ and O+ ions took place within the plasma sheet boundary layer (PSBL) as noted in some earlier studies as well. We show that in this case the PSBL corresponded to a region of enhanced electron temperature in the ionospheric F region. It is suggested that the ion outflow originates from the F region as a result of increased ambipolar diffusion. At higher altitudes, the ions could be further energized by waves, which at Cluster altitudes were observed as BBELF (broad band extra low frequency) fluctuations. The four-satellite configuration of Cluster revealed a sudden poleward expansion of the PSBL by 2 degrees during similar to 5 min. The beginning of the poleward motion of the PCB was associated with an intensification of the downward FAC at the boundary. We suggest that the downward FAC sheet at the PCB is the high-altitude counterpart of the Earthward flowing FAC produced in the vicinity of the magnetotail neutral line by the Hall effect (Sonnerup, 1979) during a short-lived reconnection pulse.
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| 7. |
- Bavassano Cattaneo, M. Bice, et al.
(författare)
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Kinetic signatures during a quasi-continuous lobe reconnection event : Cluster Ion Spectrometer (CIS) observations
- 2006
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 111:A9, s. A09212-
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Tidskriftsartikel (refereegranskat)abstract
- On 3 December 2001 the Cluster spacecraft observed a long-lasting lobe reconnection event in the southern high-latitude dusk magnetopause (MP) tailward of the cusp, during a 4 hour interval of mainly northward interplanetary magnetic field ( IMF) and of sub-Alfvenic magnetosheath flow. Almost all the MP encounters have accelerated flows ( for which the Walen test has been successfully verified by Retino et al. ( 2005)) as well as a large number of secondary populations related to reconnection, that is, ions of magnetosheath or magnetospheric origin which cross the MP either way. The detailed analysis of the distribution functions shows that the reconnection site frequently moves relative to the spacecraft, but simultaneous measurements by two spacecraft on opposite sides of the reconnection site indicate that the spacecraft's distance from the X line is small, i.e., below 3200 km. The vicinity to the X line throughout the event is probably the reason why the distribution functions characteristics agree with theoretical expectations on both sides of the reconnection site throughout this long event. Moreover, the detailed analysis of the distribution functions shows evidence, during a few time intervals, of dual reconnection, i.e., of reconnection simultaneously going on also in the northern hemisphere.
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| 8. |
- Dimmock, Andrew P., et al.
(författare)
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Direct evidence of nonstationary collisionless shocks in space plasmas
- 2019
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Ingår i: Science Advances. - : AMER ASSOC ADVANCEMENT SCIENCE. - 2375-2548. ; 5:2
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Tidskriftsartikel (refereegranskat)abstract
- Collisionless shocks are ubiquitous throughout the universe: around stars, supernova remnants, active galactic nuclei, binary systems, comets, and planets. Key information is carried by electromagnetic emissions from particles accelerated by high Mach number collisionless shocks. These shocks are intrinsically nonstationary, and the characteristic physical scales responsible for particle acceleration remain unknown. Quantifying these scales is crucial, as it affects the fundamental process of redistributing upstream plasma kinetic energy into other degrees of freedom-particularly electron thermalization. Direct in situ measurements of nonstationary shock dynamics have not been reported. Thus, the model that best describes this process has remained unknown. Here, we present direct evidence demonstrating that the transition to nonstationarity is associated with electron-scale field structures inside the shock ramp.
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| 9. |
- Duan, Suping, et al.
(författare)
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Oxygen Ions O+ Energized by Kinetic Alfven Eigenmode During Dipolarizations of Intense Substorms
- 2017
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Ingår i: Journal of Geophysical Research - Space Physics. - : American Geophysical Union (AGU). - 2169-9380 .- 2169-9402. ; 122:11, s. 11256-11273
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Tidskriftsartikel (refereegranskat)abstract
- Singly charged oxygen ions, O+, energized by kinetic Alfven wave eigenmode (KAWE) in the plasma sheet boundary layer during dipolarizations of two intense substorms, 10: 07 UT on 31 August 2004 and 18: 24 UT on 14 September 2004, are investigated by Cluster spacecraft in the magnetotail. It is found that after the beginning of the expansion phase of substorms, O+ ions are clearly energized in the direction perpendicular to the magnetic field with energy larger than 1 keV in the near-Earth plasma sheet during magnetic dipolarizations. The pitch angle distribution of these energetic O+ ions is significantly different from that of O+ ions with energy less than 1 keV before substorm onset that is in the quasi-parallel direction along the magnetic field. The KAWE with the large perpendicular unipolar electric field, E-z similar to -20 mV/m, significantly accelerates O+ ions in the direction perpendicular to the background magnetic field. We present good evidences that O+ ion origin from the ionosphere along the magnetic field line in the northward lobe can be accelerated in the perpendicular direction during substorm dipolarizations. The change of the move direction of O+ ions is useful for O+ transferring from the lobe into the central plasma sheet in the magnetotail. Thus, KAWE can play an important role in O+ ion transfer process from the lobe into the plasma sheet during intense substorms.
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| 10. |
- Eastwood, J.P., et al.
(författare)
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Multi-point observations of the Hall electromagnetic field and secondary island formation during magnetic reconnection
- 2007
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202. ; 112:A6, s. A06235-
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Tidskriftsartikel (refereegranskat)abstract
- A key feature of collisionless magnetic reconnection is the formation of Hall magnetic and electric field structure in the vicinity of the diffusion region. Here we present multi‐point Cluster observations of a reconnection event in the near‐Earth magnetotail where the diffusion region was nested by the Cluster spacecraft; we compare observations made simultaneously by different spacecraft on opposite sides of the magnetotail current sheet. This allows the spatial structure of both the electric and magnetic field to be probed. It is found that, close to the diffusion region, the magnetic field displays a symmetric quadrupole structure. The Hall electric field is symmetric, observed to be inwardly directed on both sides of the current sheet. It is large (∼40 mV m−1) on the earthward side of the diffusion region, but substantially weaker on the tailward side, suggesting a reduced reconnection rate reflected by a similar reduction in Ey. A small‐scale magnetic flux rope was observed in conjunction with these observations. This flux rope, observed very close to the reconnection site and entrained in the plasma flow, may correspond to what have been termed secondary islands in computer simulations. The core magnetic field inside the flux rope is enhanced by a factor of 3, even though the lobe guide field is negligible. Observations of the electric field inside the magnetic island show extremely strong (∼100 mV m−1) fields which may play a significant role in the particle dynamics during reconnection.
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