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Publications (10 of 14) Show all publications
Moeslinger, A., Nilsson, H., Stenberg Wieser, G., Gunell, H. & Goetz, C. (2023). Indirect observations of electric fields at comet 67P. Journal of Geophysical Research - Space Physics, 128(9), Article ID e2023JA031746.
Open this publication in new window or tab >>Indirect observations of electric fields at comet 67P
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2023 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 128, no 9, article id e2023JA031746Article in journal (Refereed) Published
Abstract [en]

No spacecraft visiting a comet has been equipped with instruments to directly measure the static electric field. However, the electric field can occasionally be estimated indirectly by observing its effects on the ion velocity distribution. We present such observations made by the Rosetta spacecraft on 19 April 2016, 35 km from the nucleus. At this time comet 67P was at a low outgassing rate and the plasma environment was relatively stable. The ion velocity distributions show the cometary ions on the first half of their gyration. We estimate the bulk drift velocity and the gyration speed from the distributions. By using the local measured magnetic field and assuming an E × B drift of the gyrocentre, we get an estimate for the average electric field driving this ion motion. We analyze a period of 13 hr, during which the plasma environment does not change drastically. We find that the average strength of the perpendicular electric field component is 0.21 mV/m. The direction of the electric field is mostly anti-sunward. This is in agreement with previous results based on different methods.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2023
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:umu:diva-214755 (URN)10.1029/2023JA031746 (DOI)2-s2.0-85171655091 (Scopus ID)
Funder
Swedish National Space Board, 132/19Swedish National Space Board, 108/18
Available from: 2023-10-03 Created: 2023-10-03 Last updated: 2023-10-03Bibliographically approved
Nilsson, H., Zhang, Q., Stenberg Wieser, G., Holmström, M., Barabash, S., Futaana, Y., . . . Wieser, M. (2023). Solar cycle variation of ion escape from Mars. Icarus, 393, Article ID 114610.
Open this publication in new window or tab >>Solar cycle variation of ion escape from Mars
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2023 (English)In: Icarus, ISSN 0019-1035, E-ISSN 1090-2643, Vol. 393, article id 114610Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Academic Press, 2023
Keywords
Magnetospheres, Mars, Mars atmosphere, Mars climate
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:umu:diva-191346 (URN)10.1016/j.icarus.2021.114610 (DOI)000953414200001 ()2-s2.0-85111018401 (Scopus ID)
Available from: 2022-01-13 Created: 2022-01-13 Last updated: 2023-05-02Bibliographically approved
Zhang, Q., Holmström, M., Wang, X.-D., Nilsson, H. & Barabash, S. (2023). The influence of solar irradiation and solar wind conditions on heavy ion escape from Mars. Journal of Geophysical Research - Space Physics, 128(10), Article ID e2023JA031828.
Open this publication in new window or tab >>The influence of solar irradiation and solar wind conditions on heavy ion escape from Mars
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2023 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 128, no 10, article id e2023JA031828Article in journal (Refereed) Published
Abstract [en]

We apply a recently proposed method to estimate heavy ion escape from Mars. The method combines in situ observations with a hybrid plasma model, which treats ions as particles and electrons as a fluid. With this method, we investigate how solar upstream conditions, including solar extreme ultraviolet (EUV) radiation, solar wind dynamic pressure, and interplanetary magnetic field (IMF) strength and cone angle, affect the heavy ion loss. The results indicate that the heavy ion escape rate is greater in high EUV conditions. The escape rate increases with increasing solar wind dynamic pressure, and decreases as the IMF strength increases. The ion escape rate is highest when the solar wind is parallel to the IMF and lowest when they are perpendicular. The plume escape rate decreases when the solar wind convective electric field increases.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2023
Keywords
hybrid model, ion escape, Mars
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:umu:diva-215942 (URN)10.1029/2023JA031828 (DOI)001086481000001 ()2-s2.0-85174732132 (Scopus ID)
Funder
Swedish National Space Board, 198/19
Available from: 2023-11-01 Created: 2023-11-01 Last updated: 2023-11-01Bibliographically approved
Nilsson, H., Möslinger, A., Williamson, H. N., Bergman, S., Gunell, H., Stenberg Wieser, G., . . . Holmström, M. (2022). Upstream solar wind speed at comet 67P: reconstruction method, model comparison, and results. Astronomy and Astrophysics, 659, Article ID A18.
Open this publication in new window or tab >>Upstream solar wind speed at comet 67P: reconstruction method, model comparison, and results
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2022 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 659, article id A18Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
EDP Sciences, 2022
Keywords
Acceleration of particles, Comets: general, Comets: individual: C67P, Plasmas, Space vehicles: instruments
National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-193059 (URN)10.1051/0004-6361/202142867 (DOI)000761966800004 ()2-s2.0-85125761748 (Scopus ID)
Funder
Swedish Research Council, 2015-04187The European Space Agency (ESA)
Available from: 2022-03-21 Created: 2022-03-21 Last updated: 2023-01-16Bibliographically approved
Persson, M., Futaana, Y., Ramstad, R., Schillings, A., Masunaga, K., Nilsson, H., . . . Barabash, S. (2021). Global Venus-Solar wind coupling and oxygen ion escape. Geophysical Research Letters, 48(4), Article ID e2020GL091213.
Open this publication in new window or tab >>Global Venus-Solar wind coupling and oxygen ion escape
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2021 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 48, no 4, article id e2020GL091213Article in journal (Refereed) Published
Abstract [en]

The present‐day Venusian atmosphere is dry, yet, in its earlier history a significant amount of water evidently existed. One important water loss process comes from the energy and momentum transfer from the solar wind to the atmospheric particles. Here, we used measurements from the Ion Mass Analyzer onboard Venus Express to derive a relation between the power in the upstream solar wind and the power leaving the atmosphere through oxygen ion escape in the Venusian magnetotail. We find that on average 0.01% of the available power is transferred, and that the percentage decreases as the available energy increases. For Mars the trend is similar, but the efficiency is higher. At Earth, the ion escape does not behave similarly, as the ion escape only increases after a threshold in the available energy is reached. These results indicate that the Venusian induced magnetosphere efficiently screens the atmosphere from the solar wind.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2021
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-176001 (URN)10.1029/2020GL091213 (DOI)000620058900054 ()2-s2.0-85101128024 (Scopus ID)
Note

Originally included in thesis in manuscript form.

Available from: 2020-10-15 Created: 2020-10-15 Last updated: 2023-10-30Bibliographically approved
Persson, M., Futaana, Y., Nilsson, H., Stenberg Wieser, G., Hamrin, M., Fedorov, A., . . . Barabash, S. (2019). Heavy Ion Flows in the Upper Ionosphere of the Venusian North Pole. Journal of Geophysical Research - Space Physics, 124(6), 4597-4607
Open this publication in new window or tab >>Heavy Ion Flows in the Upper Ionosphere of the Venusian North Pole
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2019 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 124, no 6, p. 4597-4607Article in journal (Refereed) Published
Abstract [en]

We investigate the heavy ion density and velocity in the Venusian upper ionosphere near the North Pole, using the Ion Mass Analyzer, a part of the Analyzer of Space Plasmas and Energetic Atoms 4, together with the magnetic field instruments on Venus Express. The measurements were made during June-July 2014, covering the aerobraking campaign with lowered altitude measurements (similar to 130 km). The plasma scale heights are similar to 15 km below 150-km altitude and similar to 200 km at 150-400-km altitude. A clear trend of dusk-to-dawn heavy ion flow across the polar ionosphere was found, with speeds of similar to 2-10 km/s. In addition, the flow has a significant downward radial velocity component. The flow pattern does not depend on the interplanetary magnetic field directions nor the ionospheric magnetization states. Instead, we suggest a thermal pressure gradient between the equatorial and polar terminator regions, induced by the decrease in density between the regions, as the dominant mechanism driving the ion flow. Plain Language Summary We have calculated the ion density and velocities in the Venusian polar ionosphere using measurements from the Ion Mass Analyzer on board the Venus Express spacecraft. During June-July 2014 the periapsis was lowered to similar to 130 km, which allowed for measurements down to low altitudes of the ionosphere near the North Pole. The plasma scale heights are similar to 15 km below 150-km altitude and similar to 200 km at 150-400 km, which is similar to what was found near the equatorial region by the Pioneer Venus mission. In addition, there is a clear trend of dusk-to-dawn flow, along the terminator, for the heavy ions. This is surprising, as a general flow from day-to-night is expected for the Venusian ionosphere due to the long nights and significant heating of the dayside upper atmosphere. The interplanetary magnetic field direction does not appear to affect the ion flow pattern. Instead, we propose a thermal pressure gradient as the dominant accelerating mechanism, induced by the decrease in density from the equator toward the pole.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2019
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-162017 (URN)10.1029/2018JA026271 (DOI)000477723100049 ()2-s2.0-85067394643 (Scopus ID)
Available from: 2019-08-12 Created: 2019-08-12 Last updated: 2023-03-23Bibliographically approved
Gunell, H., Maggiolo, R., Nilsson, H., Stenberg Wieser, G., Slapak, R., Lindkvist, J., . . . De Keyser, J. (2018). Why an intrinsic magnetic field does not protect a planet against atmospheric escape [Letter to the editor]. Astronomy and Astrophysics, 614, Article ID L3.
Open this publication in new window or tab >>Why an intrinsic magnetic field does not protect a planet against atmospheric escape
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2018 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 614, article id L3Article in journal, Letter (Refereed) Published
Abstract [en]

The presence or absence of a magnetic field determines the nature of how a planet interacts with the solar wind and what paths are available for atmospheric escape. Magnetospheres form both around magnetised planets, such as Earth, and unmagnetised planets, like Mars and Venus, but it has been suggested that magnetised planets are better protected against atmospheric loss. However, the observed mass escape rates from these three planets are similar (in the approximate (0.5–2) kg s−1 range), putting this latter hypothesis into question. Modelling the effects of a planetary magnetic field on the major atmospheric escape processes, we show that the escape rate can be higher for magnetised planets over a wide range of magnetisations due to escape of ions through the polar caps and cusps. Therefore, contrary to what has previously been believed, magnetisation is not a sufficient condition for protecting a planet from atmospheric loss. Estimates of the atmospheric escape rates from exoplanets must therefore address all escape processes and their dependence on the planet’s magnetisation.

Place, publisher, year, edition, pages
EDP Sciences, 2018
Keywords
Planets and satellites: magnetic fields, Planets and satellites: atmospheres, plasmas
National Category
Fusion, Plasma and Space Physics
Research subject
Space and Plasma Physics; Space Physics
Identifiers
urn:nbn:se:umu:diva-148205 (URN)10.1051/0004-6361/201832934 (DOI)000435753000001 ()2-s2.0-85049562755 (Scopus ID)
Available from: 2018-05-30 Created: 2018-05-30 Last updated: 2021-11-30Bibliographically approved
Ramstad, R., Barabash, S., Futaana, Y., Nilsson, H. & Holmström, M. (2017). Global Mars-solar wind coupling and ion escape. Journal of Geophysical Research - Space Physics, 122(8), 8051-8062
Open this publication in new window or tab >>Global Mars-solar wind coupling and ion escape
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 8, p. 8051-8062Article in journal (Refereed) Published
Abstract [en]

Loss of the early Martian atmosphere is often thought to have occurred due to an effective transfer of the solar wind energy through the Martian induced magnetic barrier to the ionosphere. We have quantified the coupling efficiency by comparing the power of the heavy ion outflow with the available power supplied by the upstream solar wind. Constraining upstream solar wind density nsw, velocity vsw, and EUV intensity IEUV/photoionizing flux FXUV in varying intervals reveals a decrease in coupling efficiency, k,with solar wind dynamic pressure as ∝ pdyn−0.74±0.13 and with FXUV as k ∝ FXUV−2.28±0.30. Despite the decreasein coupling efficiency, higher FXUV enhances the cold ion outflow, increasing the total ion escape rate as Q(FXUV) = 1010(0.82 ± 0.05)FXUV. The discrepancy between coupling and escape suggests that ion escapefrom Mars is primarily production limited in the modern era, though decreased coupling may lead to an energy-limited solar wind interaction under early Sun conditions.

Place, publisher, year, edition, pages
Washington: American Geophysical Union (AGU), 2017
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-141930 (URN)10.1002/2017JA024306 (DOI)000411788800015 ()
Available from: 2017-11-15 Created: 2017-11-15 Last updated: 2022-03-08Bibliographically approved
Ramstad, R., Barabash, S., Futaana, Y., Yamauchi, M., Nilsson, H. & Holmström, M. (2017). Mars Under Primordial Solar Wind Conditions: Mars Express Observations of the Strongest CME Detected at Mars Under Solar Cycle #24 and its Impact on Atmospheric Ion Escape. Geophysical Research Letters
Open this publication in new window or tab >>Mars Under Primordial Solar Wind Conditions: Mars Express Observations of the Strongest CME Detected at Mars Under Solar Cycle #24 and its Impact on Atmospheric Ion Escape
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2017 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007Article in journal (Refereed) Epub ahead of print
Abstract [en]

An extremely strong Coronal Mass Ejection (CME) impacted Mars on 12 July 2011, while theMars Express spacecraft was present inside the nightside ionosphere. Estimated solar wind density andspeed during the event are 39 particles cm−3 and 730 km/s, corresponding to nominal solar wind fluxat Mars when the solar system was ∼1.1 Ga old. Comparing with expected average atmospheric heavy ionfluxes under similar XUV conditions, the CME impact is found to have no significant effect on the escaperate 3.3 × 1024 s−1, with an upper limit at 1025 s−1 if the observed tail contraction is not taken into account.On the subsequent orbit, 7 h later after magnetosphere response, fluxes were only 2.4% of average. As such,even under primordial solar wind conditions we are unable to find support for a strong solar wind-driven ion escape, rather the main effect appears to be acceleration of the escaping ions by ×10–×20 typicalcharacteristic energy.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-141931 (URN)10.1002/2017GL075446 (DOI)
Available from: 2017-11-15 Created: 2017-11-15 Last updated: 2022-03-08
Ramstad, R., Barabash, S., Futaana, Y., Nilsson, H. & Holmström, M. (2016). Effects of the crustal magnetic fields on the Martian atmospheric ion escape rate. Journal of Geophysical Research - Space Physics, 43(20), 10574-10579
Open this publication in new window or tab >>Effects of the crustal magnetic fields on the Martian atmospheric ion escape rate
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2016 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 43, no 20, p. 10574-10579Article in journal (Refereed) Published
Abstract [en]

Eight years (2007–2015) of ion flux measurements from Mars Express are used to statisticallyinvestigate the influence of the Martian magnetic crustal fields on the atmospheric ion escape rate.We combine all Analyzer of Space Plasmas and Energetic Atoms/Ion Mass Analyzer (ASPERA-3/IMA)measurements taken during nominal upstream solar wind and solar extreme ultraviolet conditions tocompute global average ion distribution functions, individually for the north/south hemispheres and forvarying solar zenith angles (SZAs) of the strongest crustal magnetic field. Escape rates are subsequentlycalculated from each of the average distribution functions. The maximum escape rate (4.2 ± 1.2) × 1024 s−1 is found for SZA = 60–80, while the minimum escape rate (1.7±0.6)×1024 s−1 is found for SZA = 28–60,showing that the dayside orientation of the crustal fields significantly affects the global escape rate (p=97%). However, averaged over time, independent of SZA, we find no statistically significant difference inthe escape rates from the two hemispheres (escape from southern hemisphere 46% ± 18% of global rate).

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:umu:diva-141926 (URN)10.1002/2016GL070135 (DOI)000388293800037 ()
Available from: 2017-11-15 Created: 2017-11-15 Last updated: 2022-03-08
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