Publications (57)91.51 Total impact
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Article: On the relation between plasma escape and the Martian crustal magnetic field
Geophysical Research Letters 01/2011; 38(2):L02102. · 3.79 Impact Factor -
Article: The origin of cold ion escape from Mars
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ABSTRACT: Cold ionospheric ions dominate the plasma escape from Mars. The flow pattern versus altitude, latitude and local time suggests a fairly symmetric transport of ionospheric plasma from the dayside into the nightside/tail region of Mars. An interesting aspect of the plasma escape from Mars is the large abundance of molecular ions. This implies that the outflow source region extends down to the lower ionosphere where molecular ions dominate. It also implies that the primary energization does not contribute much to the molecular dissociation. The gentle increase of ion velocity leading to escape may explain another finding, the outflow of ionized molecular hydrogen, H2+. Because the cold ionospheric ion outflow is dominated by H+, H2+, O+ and O2+, we have made a stoichiometric analysis of the escape. Adding the total outflow of hydrogen and oxygen respectively, and taking their ratio (∑H/∑O), we get ∑H/∑O ≈1.5. Considering measurement uncertainties and other hydrogen escape processes, such as thermal/Jeans escape, the escaping H and O atoms most likely originate from water. The obvious implication is that water, a minor constituent in the Martian atmosphere, is not only highly unstable and prone to escape Mars, but in fact dominates the non-thermal mass escape from Mars.03/2009; 11:5368. -
Article: Solar forcing and planetary ion escape from Mars
Geophysical Research Letters 01/2008; 35(9):L09203. · 3.79 Impact Factor -
Article: The loss of ions from Venus through the plasma wake.
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ABSTRACT: Venus, unlike Earth, is an extremely dry planet although both began with similar masses, distances from the Sun, and presumably water inventories. The high deuterium-to-hydrogen ratio in the venusian atmosphere relative to Earth's also indicates that the atmosphere has undergone significantly different evolution over the age of the Solar System. Present-day thermal escape is low for all atmospheric species. However, hydrogen can escape by means of collisions with hot atoms from ionospheric photochemistry, and although the bulk of O and O2 are gravitationally bound, heavy ions have been observed to escape through interaction with the solar wind. Nevertheless, their relative rates of escape, spatial distribution, and composition could not be determined from these previous measurements. Here we report Venus Express measurements showing that the dominant escaping ions are O+, He+ and H+. The escaping ions leave Venus through the plasma sheet (a central portion of the plasma wake) and in a boundary layer of the induced magnetosphere. The escape rate ratios are Q(H+)/Q(O+) = 1.9; Q(He+)/Q(O+) = 0.07. The first of these implies that the escape of H+ and O+, together with the estimated escape of neutral hydrogen and oxygen, currently takes place near the stoichometric ratio corresponding to water.Nature 12/2007; 450(7170):650-3. · 36.28 Impact Factor -
Article: Geo-Effective Solar Flare Events In December 2006: Space Weather Effect on Mars and Venus Oxygen Loss to Space
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ABSTRACT: In Dec. 2006, single sunspot region produced a series of proton solar flares, up to X9.0 level on 5 Dec 2006 10:35 UT. One unique feature of this X9.0 flare is that MeV particles originated from this proton flare were observed at Venus and Mars by Venus Express (VEX) and Mars Express (MEX), which are respectively located away from Earth by nearly +160° and -160° as viewed from the Sun. On 5 Dec 2006, the plasma instruments ASPERA-3 and ASPERA-4 on board MEX and VEX have detected a large enhancement in their respective background count level, which is a typical signature of intensive MeV particle flux. The timing of these enhancements were consistent with the estimated field-aligned travel time along the Parker spiral from the site of X9.0 flare to Venus and Mars. The Mars Express data indicate a one-order enhancement in the heavy ion outflow from the Martian atmosphere during the SEP period. This is the first observation of the increase of escaping flux at Mars during a violent solar activity. This suggests that the solar EUV flux levels also significantly affect the atmospheric loss from unmagnetized planets.AGU Fall Meeting Abstracts. 11/2007; -1:1087. -
Article: Global Response of Martian Plasma Environment to an Interplanetary Structure: From Ena and Plasma Observations at Mars
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ABSTRACT: As a part of the global plasma environment study of Mars and its response to the solar wind, we have analyzed a peculiar case of the subsolar energetic neutral atom (ENA) jet observed on June 7, 2004 by the Neutral Particle Detector (NPD) on board the Mars Express satellite. The “subsolar ENA jet” is generated by the interaction between the solar wind and the Martian exosphere, and is one of the most intense sources of ENA flux observed in the vicinity of Mars. On June 7, 2004 (orbit 485 of Mars Express), the NPD observed a very intense subsolar ENA jet, which then abruptly decreased within ∼10 sec followed by quasi-periodic (∼1 min) flux variations. Simultaneously, the plasma sensors detected a solar wind structure, which was most likely an interplanetary shock surface. The abrupt decrease of the ENA flux and the quasi-periodic flux variations can be understood in the framework of the global response of the Martian plasma obstacle to the interplanetary shock. The generation region of the subsolar ENA jet was pushed towards the planet by the interplanetary shock; and therefore, Mars Express went out of the ENA jet region. Associated global vibrations of the Martian plasma obstacle may have been the cause of the quasi-periodic flux variations of the ENA flux at the spacecraft location.Space Science Reviews 09/2006; 126(1):315-332. · 3.61 Impact Factor -
Article: Locations of Atmospheric Photoelectron Energy Peaks Within the Mars Environment
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ABSTRACT: By identifying peaks in the photoelectron spectrum produced by photoionization of CO2 in the Martian atmosphere, we have conducted a pilot study to determine the locations of these photoelectrons in the space around Mars. The significant result of this study is that these photoelectrons populate a region around Mars bounded externally by the magnetic pileup boundary, and internally by the lowest altitude of our measurements (∼250 km) on the dayside and by a cylinder of approximately the planetary radius on the nightside. It is particularly noteworthy that the photoelectrons on the nightside are observed from the terminator plane tailward to a distance of ∼3 R M, the Mars Express apoapsis. The presence of the atmospherically generated photoelectrons on the nightside of Mars may be explained by direct magnetic field line connection between the nightside observation locations and the Martian dayside ionosphere. Thus the characteristic photoelectron peaks may be used as tracers of magnetic field lines for the study of the magnetic field configuration and particle transport in the Martian environment.Space Science Reviews 09/2006; 126(1):389-402. · 3.61 Impact Factor -
Article: Energisation of O+ and O+2 Ions at Mars: An Analysis of a 3-D Quasi-Neutral Hybrid Model Simulation
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ABSTRACT: We have studied the loss of O+ and O+ 2 ions at Mars with a numerical model. In our quasi-neutral hybrid model ions (H+, He++, O+, O+ 2) are treated as particles while electrons form a massless charge-neutralising fluid. The employed model version does not include the Martian magnetic field resulting from the crustal magnetic anomalies. In this study we focus the Martian nightside where the ASPERA instrument on the Phobos-2 spacecraft and recently the ASPERA-3 instruments on the Mars Express spacecraft have measured the proprieties of escaping atomic and molecular ions, in particular O+ and O+ 2 ions. We study the ion velocity distribution and how the escaping planetary ions are distributed in the tail. We also create similar types of energy-spectrograms from the simulation as were obtained from ASPERA-3 ion measurements. We found that the properties of the simulated escaping planetary ions have many qualitative and quantitative similarities with the observations made by ASPERA instruments. The general agreement with the observations suggest that acceleration of the planetary ions by the convective electric field associated with the flowing plasma is the key acceleration mechanism for the escaping ions observed at Mars.Space Science Reviews 09/2006; 126(1):39-62. · 3.61 Impact Factor -
Article: Solar wind-induced atmospheric erosion at Mars: first results from ASPERA-3 on Mars Express.
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ABSTRACT: The Analyzer of Space Plasma and Energetic Atoms (ASPERA) on board the Mars Express spacecraft found that solar wind plasma and accelerated ionospheric ions may be observed all the way down to the Mars Express pericenter of 270 kilometers above the dayside planetary surface. This is very deep in the ionosphere, implying direct exposure of the martian topside atmosphere to solar wind plasma forcing. The low-altitude penetration of solar wind plasma and the energization of ionospheric plasma may be due to solar wind irregularities or perturbations, to magnetic anomalies at Mars, or both.Science 10/2004; 305(5692):1933-6. · 31.20 Impact Factor -
Article: ASPERA-3: analyser of space plasmas and energetic ions for Mars Express
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ABSTRACT: The ASPERA-3 (Analyser of Space Plasma and Energetic Atoms) instrument of Mars Express is designed to study the solar wind-Mars atmosphere interaction and to characterise the plasma and neutral gas environment in near-Mars space through energetic neutral atom (ENA) imaging and local charged-particle measurements. The studies address the fundamental question: how strongly do the interplanetary plasma and electromagnetic fields affect the martian atmosphere? This question is directly related to the problem of martian dehydration. The instrument comprises four sensors; two ENA sensors, and electron and ion spectrometers. The Neutral Particle Imager (NPI) measures the integral ENA flux (0.1-60 keV) with no mass and energy resolution but with high angular resolution. The Neutral Particle Detector (NPD) measures the ENA flux, resolving energy (0.1-10 keV) and mass (H and O) with a coarse angular resolution. The electron spectrometer (ELS) is a standard top-hat electrostatic analyser of a very compact design. These three sensors are mounted on a scanning platform providing 4π coverage. The instrument includes an ion mass composiotion sensor, IMA (Ion Mass Analyser). Mechanically, IMA is a separate unit connected by a cable to the ASPERA-3 main unit. IMA provides ion measuremets in the energy range 0.01-40 keV/q for the main ion components H+, He2+, He+, O+, with 20-80 amu/q.07/2004; 1240:121-139. -
Article: The present understanding of the cusp
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ABSTRACT: Knowledge learnt on the dynamics and topology of the polar cusp from in situ plasma measurements primarily on board low and medium altitude satellite is reviewed. The polar cusp, first identified from low altitude orbiting satellites, is the only region in the topside terrestrial ionosphere that maintains continuous contact with plasma. The continuous inflow of plasma through the cusp leads to a direct transfer of solar wind energy and momentum to the ionosphere and atmosphere. Thus, the cusp represents a particular 'hot spot' in the solar terrestrial relationship. New improved magnetic field mapping models have helped elucidating the connection of the low altitude cusp to the magnetospheric boundary region.11/1991; 330:83-95. -
Article: A comet-like escape of ionospheric plasma from Mars
Geophysical Research Letters, v.35 (2008). -
Article: First ENA observations at Mars: Subsolar ENA jet
Icarus, v.182, 413-423 (2006). -
Article: Solar wind plasma protrusion into the martian magnetosphere: ASPERA-3 observations
Icarus, v.182, 343-349 (2006). -
Article: The loss of ions from Venus through the plasma wake
Nature, v.450, 650-653 (2007). -
Article: The atmospheric origin of cold ion escape from Mars
Geophysical Research Letters, v.36 (2009). -
Article: Hydrogen exosphere at Mars: Pickup protons and their acceleration at the bow shock
Geophysical Research Letters, v.33 (2006). -
Article: First ENA observations at Mars: Charge exchange ENAs produced in the magnetosheath
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ABSTRACT: Measurements of energetic neutral atoms (ENA) generated in the magnetosheath at Mars are reported. These ENAs are the result of charge exchange collisions between solar wind protons and neutral oxygen and hydrogen in the exosphere of Mars. The peak of the observed ENA flux is . For the case studied here, i.e., the passage of Mars Express through the martian magnetosheath around 20:15 UT on 3 May 2004, the measurements agree with an analytical model of the ENA production at the planet. It is possible to find parameter values in the model such that the observed peak in the ENA count rate during the spacecraft passage through the magnetosheath is reproduced.Icarus. -
Article: Venusian bow shock as seen by the ASPERA-4 ion instrument on Venus Express
Journal of Geophysical Research, v.115 (2010). -
Article: IMF direction derived from cycloid-like ion distributions observed by Mars Express
Space Science Review, v.126, 239-266 (2006).
Top co-authors
Top Journals
- Space Science Reviews (3)
- Geophysical Research Letters (2)
- Planetary and Space Science (1)
- Icarus (1)
- Science (1)
Institutions
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1991–2009
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Swedish Institute of Space Physics
Kiruna, Norrbotten, Sweden
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2006
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University of Helsinki
Helsinki, Province of Southern Finland, Finland
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