| 1. |
- Alfvén, Hannes, et al.
(författare)
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Voyager saturnian ring measurements and the early history of the solar-system
- 1986
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Ingår i: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 34:2, s. 145-154
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Tidskriftsartikel (refereegranskat)abstract
- The mass distribution in the Saturnian ring system is investigated and compared with predictions from the plasma cosmogony. According to this theory, the matter in the rings has once been in the form of a magnetized plasma, in which the gravitation is balanced partly by the centrifugal force and partly by the electromagnetic forces. As the plasma is neutralized, the electromagnetic forces disappear and the matter can be shown to fall in to of the original saturnocentric distance. This causes the so called “cosmogonic shadow effect”, which has been demonstrated earlier for the asteroidal belt and in the large scale structure of the Saturnian ring system.The relevance of the cosmogonic shadow effect is investigated for parts of the fine structures of the Saturnian ring system. It is shown that many structures of the present ring system can be understood as shadows and antishadows of cosmogonic origin. These appear in the form of double rings centered around a position a factor 0.64 (slightly less than) closer to Saturn than the causing feature. Voyager data agree with an accuracy better than 1%.
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| 2. |
- Blomberg, Lars
(författare)
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Mercury's magnetosphere, exosphere and surface : Low-frequency field and wave measurements as a diagnostic tool
- 1997
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Ingår i: Planetary and Space Science. - 0032-0633 .- 1873-5088. ; 45:1, s. 143-148
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Tidskriftsartikel (refereegranskat)abstract
- Diagnostics that can be made with combined electric and magnetic field measurements at Mercury are reviewed. Fundamental electrodynamic questions which can be answered by means of a Mercury Orbiter are discussed. These include, solar wind-magnetosphere coupling, coupling to low altitude, exospheric or planetary surface conductivity, auroral particle acceleration, and magnetospheric substorms. It is concluded that a comprehensive instrumentation package for low-frequency fields and waves on a future Mercury Orbiter mission may yield significant new information of interest to magnetospheric as well as to planetary physics in general. (C) 1997 Elsevier Science Ltd.
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| 3. |
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| 4. |
- Marklund, Göran, et al.
(författare)
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Rocket measurements of electric fields, electron density and temperature during different phases of auroral substorms
- 1981
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Ingår i: Planetary and Space Science. - : Elsevier BV. - 0032-0633 .- 1873-5088. ; 29:2, s. 249-259
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Tidskriftsartikel (refereegranskat)abstract
- On 27 January 1979, three rocket payloads were launched from Kiruna, Sweden into different phases of two successive auroral substorrns. Among other experiments, the payloads carried the RIT double probe electric field experiments providing electric field, electron density and temperature data which are presented here. These data supported by rocket particle observations are discussed mainly in association with ground-based observations (magnetometer, TV) and very briefly with GEOS electric field data. The motions of the auroral forms as obtained from auroral pictures are compared with E × B/B2 drifts and the currents calculated from the rocket electric field and density measurements with the equivalent current system deduced from ground-based magnetometer data (Scandinavian Magnetometer Array).
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| 5. |
- SANDAHL, I, et al.
(författare)
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Electron populations above the nightside auroral oval during magnetic quiet times
- 1990
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Ingår i: Planetary and Space Science. - : Pergamon Press. - 0032-0633 .- 1873-5088. ; 38:8, s. 1031-1049
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Tidskriftsartikel (refereegranskat)abstract
- In several studies of particle morphology above the nightside auroral oval, the electrons have been divided into two separate spatial regions, often called the BPS (from "boundary plasma sheet") and the CPS (from "central plasma sheet") (Winningham et al., 1975, J. geophys. Res. 80, 3148). The names were derived from the source regions suggested by Winningham et al. In many cases this classification has worked well, but there are also many cases in which it has not. In this paper an alternative classification is proposed and explored by investigating the spatial distribution of electrons at altitudes between 2000 and 13,500 km, using particle spectrograms from the Viking satellite. A major difference between the newly proposed and the earlier classification is that spatial regions of populations may overlap in this new scheme. Electrons above the auroral oval could be divided into two populations. The first one is spatially unstructured and has a characteristic energy of a few kiloelectron volts. It is usually trapped in its equatorward part, while it is isotropic in its poleward part. The second one is spatially structured and normally has a characteristic energy of 100 eV or less. It is always present when there are signs of electron acceleration along magnetic field lines. The global distributions of both the structured and the unstructured electrons are ring-shaped. The two regions partially overlap, and the average latitude of the structured electrons is higher than the average latitude of the unstructured electrons. The majority of bright auroras appear in the region of overlap. The average poleward edge of the overlap region seems to coincide with the average poleward edge of region 1 field-aligned currents. We suggest that this boundary maps to the boundary between the central plasma sheet and the plasma sheet boundary layer. We also suggest that the sources for the region where only structured electrons are present are the low-latitude boundary layer and plasma sheet boundary layer. The conclusions concerning source regions are supported by mapping of the particle population regions into the equatorial plane of the magnetosphere using the Tsyganenko (1987, Planet. Space Sci. 35, 1347) magnetic field model. The average boundary between region 1 and region 2 field-aligned currents in the afternoon and evening is approximately at the average equatorward boundary of unstructured electrons. Through the midnight, morning and prenoon sectors it is at the average equatorward boundary of structured electrons.
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| 6. |
- Sorriso-Valvo, Luca, et al.
(författare)
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Intermittency in plasma turbulence
- 2001
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Ingår i: Planetary and Space Science. - 0032-0633 .- 1873-5088. ; 49:12, s. 1193-1200
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Tidskriftsartikel (refereegranskat)
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| 7. |
- Wurz, Peter, et al.
(författare)
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Particle populations in Mercury's magnetosphere
- 2001
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Ingår i: Planetary and Space Science. - 0032-0633 .- 1873-5088. ; 49:14-15, s. 1643-1653
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Tidskriftsartikel (refereegranskat)abstract
- Observations by Mariner 10 during its first and third flybys showed that Mercury possesses an intrinsic magnetic field resulting in a small magnetosphere that can keep the solar wind from directly interacting with the planet's surface under usual conditions. Since Mercury occupies a large fraction of its magnetosphere, regions of trapped charged particles in the inner magnetosphere, the plasmasphere and the energetic radiation belts, would all be absent. During the first flyby, energetic particle bursts were detected and interpreted as hermean substroms analogous to the terrestrial magnetosphere. Moreover, during this flyby, ULF waves and field-aligned currents were detected in the data. Earth-based observations of Na, K, and Ca populations in the exosphere strongly suggest the existence of dynamic magnetospheric processes at high latitudes interacting with the planet's surface.
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| 8. |
- Abdellaoui, G., et al.
(författare)
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Meteor studies in the framework of the JEM-EUSO program
- 2017
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Ingår i: Planetary and Space Science. - : Elsevier. - 0032-0633 .- 1873-5088. ; 143, s. 245-255
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Tidskriftsartikel (refereegranskat)abstract
- We summarize the state of the art of a program of UV observations from space of meteor phenomena, a secondary objective of the JEM-EUSO international collaboration. Our preliminary analysis indicates that JEM-EUSO, taking advantage of its large FOV and good sensitivity, should be able to detect meteors down to absolute magnitude close to 7. This means that JEM-EUSO should be able to record a statistically significant flux of meteors, including both sporadic ones, and events produced by different meteor streams. Being unaffected by adverse weather conditions, JEM-EUSO can also be a very important facility for the detection of bright meteors and fireballs, as these events can be detected even in conditions of very high sky background. In the case of bright events, moreover, exhibiting some persistence of the meteor train, preliminary simulations show that it should be possible to exploit the motion of the ISS itself and derive at least a rough 3D reconstruction of the meteor trajectory. Moreover, the observing strategy developed to detect meteors may also be applied to the detection of nuclearites, exotic particles whose existence has been suggested by some theoretical investigations. Nuclearites are expected to move at higher velocities than meteoroids, and to exhibit a wider range of possible trajectories, including particles moving upward after crossing the Earth. Some pilot studies, including the approved Mini-EUSO mission, a precursor of JEM-EUSO, are currently operational or in preparation. We are doing simulations to assess the performance of Mini-EUSO for meteor studies, while a few meteor events have been already detected using the ground-based facility EUSO-TA.
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| 9. |
- Aizawa, S., et al.
(författare)
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Cross-comparison of global simulation models applied to Mercury's dayside magnetosphere
- 2021
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Ingår i: Planetary and Space Science. - : Elsevier. - 0032-0633 .- 1873-5088. ; 198
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Tidskriftsartikel (refereegranskat)abstract
- We present the first comparison of multiple global simulations of the solar wind interaction with Mercury's dayside magnetosphere, conducted in the framework of the international collaborative project SHOTS - Studies on Hermean magnetosphere Oriented Theories and Simulations. Two 3D magnetohydrodynamic and two 3D hybrid simulation codes are used to investigate the global response of the Hermean magnetosphere without its exosphere to a northward-oriented interplanetary magnetic field. We cross-compare the results of the four codes for a theoretical case and a MESSENGER orbit with similar upstream plasma conditions. The models agree on bowshock and magnetopause locations at 2.1 ± 0.11 and 1.4 ± 0.1 Mercury planetary radii, respectively. The latter locations may be influenced by subtle differences in the treatment of the plasma boundary at the planetary surface. The predicted magnetosheath thickness varies less between the codes. Finally, we also sample the plasma data along virtual trajectories of BepiColombo's Magnetospheric and Planetary Orbiter. Our ability to accurately predict the structure of the Hermean magnetosphere aids the analysis of the onboard plasma measurements of past and future magnetospheric missions.
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| 10. |
- Alday, Juan, et al.
(författare)
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New constraints on Ganymede's hydrogen corona : Analysis of Lyman-alpha emissions observed by HST/STIS between 1998 and 2014
- 2017
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Ingår i: Planetary and Space Science. - : Elsevier. - 0032-0633 .- 1873-5088. ; 148, s. 35-44
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Tidskriftsartikel (refereegranskat)abstract
- Far-ultraviolet observations of Ganymede's atmospheric emissions were obtained with the Space Telescope Imaging Spectrograph (STIS) onboard of the Hubble Space Telescope (HST) on several occasions between 1998 and 2014. We analyze the Lyman-alpha emission from four HST campaigns in order to constrain the abundance and variation of atomic hydrogen in Ganymede's atmosphere. We apply a forward model that estimates surface reflection and resonant scattering in an escaping corona of the solar Lyman-alpha flux, taking into account the effects of the hydrogen in the interplanetary medium. The atmospheric emissions around Ganymede's disk derived for the observations taken between 1998 and 2011 are consistent with a hydrogen corona in the density range of (5-8) x 10(3) cm(-3) at the surface. The hydrogen density appears to be generally stable in that period. In 2014, Ganymede's corona brightness is approximately 3 times lower during two observations of Ganymede's trailing hemisphere and hardly detectable at all during two observations of the leading hemisphere. We also investigate extinction of Ganymede's coronal emissions in the Earth's upper atmosphere or geocorona. For small Doppler shifts, resonant scattering in the geocorona of the moon corona emissions can effectively reduce the brightness observed by HST. In the case of the 2014 leading hemisphere observations, an estimated extinction of 80% might explain the non-detection of Ganymede's hydrogen corona. Geocoronal extinction might also explain a previously detected hemispheric difference from Callisto's hydrogen corona.
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