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Publications (10 of 40) Show all publications
Wahlund, J.-E., Morooka, M. W., Hadid, L. Z., Persoon, A. M., Farrell, W. M., Gurnett, D. A., . . . Vigren, E. (2018). In situ measurements of Saturn's ionosphere show that it is dynamic and interacts with the rings. Science, 359(6371), 66-68
Open this publication in new window or tab >>In situ measurements of Saturn's ionosphere show that it is dynamic and interacts with the rings
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2018 (English)In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 359, no 6371, p. 66-68Article in journal (Refereed) Published
Abstract [en]

The ionized upper layer of Saturn's atmosphere, its ionosphere, provides a closure of currents mediated by the magnetic field to other electrically charged regions (for example, rings) and hosts ion-molecule chemistry. In 2017, the Cassini spacecraft passed inside the planet's rings, allowing in situ measurements of the ionosphere. The Radio and Plasma Wave Science instrument detected a cold, dense, and dynamic ionosphere at Saturn that interacts with the rings. Plasma densities reached up to 1000 cubic centimeters, and electron temperatures were below 1160 kelvin near closest approach. The density varied between orbits by up to two orders of magnitude. Saturn's A- and B-rings cast a shadow on the planet that reduced ionization in the upper atmosphere, causing a north-south asymmetry.

National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-341494 (URN)10.1126/science.aao4134 (DOI)000419324700067 ()29229651 (PubMedID)
Available from: 2018-02-21 Created: 2018-02-21 Last updated: 2018-02-21Bibliographically approved
Fowler, C. M., Andersson, L., Halekas, J., Espley, J. R., Mazelle, C., Coughlin, E. R., . . . Jakosky, B. (2017). Electric and magnetic variations in the near-Mars environment. Journal of Geophysical Research - Space Physics, 122(8), 8536-8559
Open this publication in new window or tab >>Electric and magnetic variations in the near-Mars environment
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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. 8536-8559Article in journal (Refereed) Published
Abstract [en]

For the first time at Mars the statistical distribution of (1-D) electric field wave power in the magnetosphere is presented, along with the distribution of magnetic field wave power, as observed by the Mars Atmosphere and Volatile EvolutioN spacecraft from the first 14.5months of the mission. Wave power in several different frequency bands was investigated, and the strongest wave powers were observed at the lowest frequencies. The presented statistical studies suggest that the full thermalization of ions within the magnetosheath does not appear to occur, as has been predicted by previous studies. Manual inspection of 140 periapsis passes on the dayside shows that Poynting fluxes (at 2-16 Hz) between similar to 10(-11) and 10(-8) Wm(-2) reach the upper ionosphere for all 140 cases. Wave power is not observed in the ionosphere for integrated electron densities greater than 10(10.8)cm(-2), corresponding to typical depths of 100-200 km. The observations presented support previous suggestions that energy from the Mars-solar wind interaction can propagate into the upper ionosphere and may provide an ionospheric heating source. Upstream of the shock, the orientation of the solar wind interplanetary magnetic field was shown to significantly affect the statistical distribution of wave power, based on whether the spacecraft was likely magnetically connected to the shock or not-something that is predicted but has not been quantitatively shown at Mars before. In flight performance and caveats of the Langmuir Probe and Waves electric field power spectra are also discussed.

Keywords
magnetic, electric, wave, power, Mars, MAVEN
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-336649 (URN)10.1002/2016JA023411 (DOI)000411788800047 ()
Available from: 2017-12-15 Created: 2017-12-15 Last updated: 2017-12-15Bibliographically approved
Witasse, O., Sanchez-Cano, B., Mays, M. L., Kajdic, P., Opgenoorth, H., Elliott, H. A., . . . Altobelli, N. (2017). Interplanetary coronal mass ejection observed at STEREO-A, Mars, comet 67P/Churyumov-Gerasimenko, Saturn, and New Horizons en route to Pluto: Comparison of its Forbush decreases at 1.4, 3.1, and 9.9 AU. Journal of Geophysical Research - Space Physics, 122(8), 7865-7890
Open this publication in new window or tab >>Interplanetary coronal mass ejection observed at STEREO-A, Mars, comet 67P/Churyumov-Gerasimenko, Saturn, and New Horizons en route to Pluto: Comparison of its Forbush decreases at 1.4, 3.1, and 9.9 AU
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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. 7865-7890Article in journal (Refereed) Published
Abstract [en]

We discuss observations of the journey throughout the Solar System of a large interplanetary coronal mass ejection (ICME) that was ejected at the Sun on 14 October 2014. The ICME hit Mars on 17 October, as observed by the Mars Express, Mars Atmosphere and Volatile EvolutioN Mission (MAVEN), Mars Odyssey, and Mars Science Laboratory (MSL) missions, 44h before the encounter of the planet with the Siding-Spring comet, for which the space weather context is provided. It reached comet 67P/Churyumov-Gerasimenko, which was perfectly aligned with the Sun and Mars at 3.1 AU, as observed by Rosetta on 22 October. The ICME was also detected by STEREO-A on 16 October at 1 AU, and by Cassini in the solar wind around Saturn on the 12 November at 9.9AU. Fortuitously, the New Horizons spacecraft was also aligned with the direction of the ICME at 31.6 AU. We investigate whether this ICME has a nonambiguous signature at New Horizons. A potential detection of this ICME by Voyager 2 at 110-111 AU is also discussed. The multispacecraft observations allow the derivation of certain properties of the ICME, such as its large angular extension of at least 116 degrees, its speed as a function of distance, and its magnetic field structure at four locations from 1 to 10 AU. Observations of the speed data allow two different solar wind propagation models to be validated. Finally, we compare the Forbush decreases (transient decreases followed by gradual recoveries in the galactic cosmic ray intensity) due to the passage of this ICME at Mars, comet 67P, and Saturn.

Keywords
interplanetary coronal mass ejection, Forbush decrease, Mars, comet 67P, Saturn, New Horizons
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-336648 (URN)10.1002/2017JA023884 (DOI)000411788800002 ()
Funder
Swedish National Space Board, 135/13Swedish Research Council, 621-2013-4191
Available from: 2017-12-15 Created: 2017-12-15 Last updated: 2017-12-15Bibliographically approved
Nemec, F., Morgan, D. D., Fowler, C. M., Kopf, A. J., Andersson, L., Gurnett, D. A., . . . Truhlik, V. (2017). Ionospheric Electron Densities at Mars: Comparison of Mars Express Ionospheric Sounding and MAVEN Local Measurements. Journal of Geophysical Research - Space Physics, 122(12), 12393-12405
Open this publication in new window or tab >>Ionospheric Electron Densities at Mars: Comparison of Mars Express Ionospheric Sounding and MAVEN Local Measurements
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 12, p. 12393-12405Article in journal (Refereed) Published
Abstract [en]

We present the first direct comparison of Martian ionospheric electron densities measured by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) topside radar sounder on board the Mars Express spacecraft and by the Langmuir Probe and Waves (LPW) instrument on board the Mars Atmosphere and Volatile Evolution Mission (MAVEN) spacecraft. As low electron densities are not measured by MARSIS due to the low power radiated at low sounding frequencies, MARSIS electron density profiles between the local electron density and the first data point from the ionospheric sounding (similar to 104 cm(-3)) rely on an empirical electron density profile shape. We use the LPW electron density measurements to improve this empirical description and thereby the MARSIS-derived electron density profiles. We further analyze four coincident events, where the two instruments were measuring within a 5 degrees solar zenith angle interval within 1 h. The differences between the electron densities measured by the MARSIS and LPW instruments are found to be within a factor of 2 in 90% of measurements. Taking into account the measurement precision and different locations and times of the measurements, these differences are within the estimated uncertainties.

Place, publisher, year, edition, pages
AMER GEOPHYSICAL UNION, 2017
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-342473 (URN)10.1002/2017JA024629 (DOI)000422735500023 ()
Available from: 2018-02-21 Created: 2018-02-21 Last updated: 2018-02-21Bibliographically approved
Sanchez-Cano, B., Hall, B. E., Lester, M., Mays, M. L., Witasse, O., Ambrosi, R., . . . Reyes-Ayala, K. I. (2017). Mars plasma system response to solar wind disturbances during solar minimum. Journal of Geophysical Research - Space Physics, 122(6), 6611-6634
Open this publication in new window or tab >>Mars plasma system response to solar wind disturbances during solar minimum
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2017 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 122, no 6, p. 6611-6634Article in journal (Refereed) Published
Abstract [en]

This paper is a phenomenological description of the ionospheric plasma and induced magnetospheric boundary (IMB) response to two different types of upstream solar wind events impacting Mars in March 2008, at the solar minimum. A total of 16 Mars Express orbits corresponding to five consecutive days is evaluated. Solar TErrestrial RElations Observatory-B (STEREO-B) at 1AU and Mars Express and Mars Odyssey at 1.644AU detected the arrival of a small transient interplanetary coronal mass ejection (ICME-like) on the 6 and 7 of March, respectively. This is the first time that this kind of small solar structure is reported at Mars's distance. In both cases, it was followed by a large increase in solar wind velocity that lasted for similar to 10days. This scenario is simulated with the Wang-Sheeley-Arge (WSA) - ENLIL + Cone solar solar wind model. At Mars, the ICME-like event caused a strong compression of the magnetosheath and ionosphere, and the recovery lasted for similar to 3 orbits (similar to 20h). After that, the fast stream affected the upper ionosphere and the IMB, which radial and tangential motions in regions close to the subsolar point are analyzed. Moreover, a compression in the Martian plasma system is also observed, although weaker than after the ICME-like impact, and several magnetosheath plasma blobs in the upper ionosphere are detected by Mars Express. We conclude that, during solar minimum and at aphelion, small solar wind structures can create larger perturbations than previously expected in the Martian system.

Keywords
ICME transient, fast solar wind stream, ionosphere of Mars, Martian plasma system, Martian boundaries, solar minimum
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-331894 (URN)10.1002/2016JA023587 (DOI)000405534800049 ()
Available from: 2017-10-27 Created: 2017-10-27 Last updated: 2017-10-27Bibliographically approved
Dubinin, E., Fraenz, M., Paetzold, M., Andrews, D. J., Vaisberg, O., Zelenyi, L. & Barabash, S. (2017). Martian ionosphere observed by Mars Express. 2. Influence of solar irradiance on upper ionosphere and escape fluxes. Planetary and Space Science, 145, 1-8
Open this publication in new window or tab >>Martian ionosphere observed by Mars Express. 2. Influence of solar irradiance on upper ionosphere and escape fluxes
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2017 (English)In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 145, p. 1-8Article in journal (Refereed) Published
Abstract [en]

We present multi-instrument observations of the effects of solar irradiance on the upper Martian ionosphere and escape fluxes based on Mars Express measurements obtained over almost 12 years. It is shown that the variations in the upper ionosphere caused by solar irradiance lead to significant changes in the trans-terminator fluxes of low-energy ions and total ion losses through the tail. The observed dependence of the electron number density in the upper ionosphere at altitudes above 300 km on solar irradiance implies that the ionosphere at such altitudes was denser by a factor of ten during the periods of solar maxima in solar cycles 22-23. Correspondingly, the trans terminator fluxes of cold ions and escape fluxes through the tail were also significantly higher. We estimate an increase of total ion losses through the tail during these solar maxima by a factor of 5-6.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2017
Keywords
Mars, Solar irradiance, Ionosphere, Mars express, Escape
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-336447 (URN)10.1016/j.pss.2017.07.002 (DOI)000411534100001 ()
Funder
Swedish National Space Board, DNR 162/14Swedish Research Council, DNR 621-2014-5526
Available from: 2017-12-14 Created: 2017-12-14 Last updated: 2017-12-14Bibliographically approved
Hall, B. E., Lester, M., Nichols, J. D., Sanchez-Cano, B., Andrews, D. J., Opgenoorth, H. J. & Fraenz, M. (2016). A survey of superthermal electron flux depressions, or "electron holes," within the illuminated Martian induced magnetosphere. Journal of Geophysical Research - Space Physics, 121(5), 4835-4857
Open this publication in new window or tab >>A survey of superthermal electron flux depressions, or "electron holes," within the illuminated Martian induced magnetosphere
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2016 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 5, p. 4835-4857Article in journal (Refereed) Published
Abstract [en]

Since Mars lacks a global intrinsic magnetic field, the solar wind interacts directly with the Martian upper atmosphere and ionosphere. The presence of localized intense remnant crustal magnetic fields adds to this interaction, making the Martian plasma system a unique environment within the solar system. Rapid reductions in the electron flux, referred to as electron holes, occur within the Martian induced magnetosphere (IM). We present a statistical analysis of this phenomenon identified from proxy measurements of the electron flux derived from measurements by the Analyser of Space Plasmas and Energetic Neutral Atoms Electron Spectrometer experiment on board the Mars Express (MEX) spacecraft. The study is completed for the period of 9 February 2004 to 9 May 2014. Electron holes are observed within the IM in more than 56% of MEX orbits during this study period, occurring predominantly at altitudes less than 1300km, with the majority in the negative X Mars-Centric Solar Orbital direction. The spatial distribution above the surface of Mars is observed to bear close resemblance to that of the crustal magnetic fields as predicted by the Cain et al. [] magnetic field model, suggesting that they play an important role in the formation of these phenomena.

Keywords
electron holes, plasma void, electron depression, induced magnetosphere, Mars' plasma environment, Mars Express
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-300976 (URN)10.1002/2015JA021866 (DOI)000380025500069 ()
Funder
Swedish National Space Board, DNR 162/14Swedish Research Council, DNR 621-2014-5526
Available from: 2016-08-23 Created: 2016-08-16 Last updated: 2017-11-28Bibliographically approved
Hall, B. E., Lester, M., Sanchez-Cano, B., Nichols, J. D., Andrews, D. J., Edberg, N. J. T., . . . Orosei, R. (2016). Annual variations in the Martian bow shock location as observed by the Mars Express mission. Journal of Geophysical Research - Space Physics, 121(11), 11474-11494
Open this publication in new window or tab >>Annual variations in the Martian bow shock location as observed by the Mars Express mission
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2016 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 11, p. 11474-11494Article in journal (Refereed) Published
Abstract [en]

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.

National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-313413 (URN)10.1002/2016JA023316 (DOI)000390403400056 ()
Funder
Swedish National Space Board, DNR 162/14, DNR 135/13Swedish Research Council, DNR 621-2014-5526, 621-2013-4191
Available from: 2017-01-25 Created: 2017-01-19 Last updated: 2017-11-29Bibliographically approved
Edberg, N. J. T., Alho, M., André, M., Andrews, D. J., Behar, E., Burch, J. L., . . . Volwerk, M. (2016). CME impact on comet 67P/Churyumov-Gerasimenko. Paper presented at 50th ESLAB Symposium, MAR 14-18, 2016, Leiden, NETHERLANDS. Monthly notices of the Royal Astronomical Society, 462, S45-S56
Open this publication in new window or tab >>CME impact on comet 67P/Churyumov-Gerasimenko
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2016 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 462, p. S45-S56Article in journal (Refereed) Published
Abstract [en]

We present Rosetta observations from comet 67P/Churyumov-Gerasimenko during the impact of a coronal mass ejection (CME). The CME impacted on 2015 Oct 5-6, when Rosetta was about 800 km from the comet nucleus, and 1.4 au from the Sun. Upon impact, the plasma environment is compressed to the level that solar wind ions, not seen a few days earlier when at 1500 km, now reach Rosetta. In response to the compression, the flux of suprathermal electrons increases by a factor of 5-10 and the background magnetic field strength increases by a factor of similar to 2.5. The plasma density increases by a factor of 10 and reaches 600 cm(-3), due to increased particle impact ionization, charge exchange and the adiabatic compression of the plasma environment. We also observe unprecedentedly large magnetic field spikes at 800 km, reaching above 200 nT, which are interpreted as magnetic flux ropes. We suggest that these could possibly be formed by magnetic reconnection processes in the coma as the magnetic field across the CME changes polarity, or as a consequence of strong shears causing Kelvin-Helmholtz instabilities in the plasma flow. Due to the limited orbit of Rosetta, we are not able to observe if a tail disconnection occurs during the CME impact, which could be expected based on previous remote observations of other CME-comet interactions.

Keywords
Sun: coronal mass ejections (CMEs), solar wind, comets: individual: 67P/Churyumov-Gerasimenko
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-328419 (URN)10.1093/mnras/stw2112 (DOI)000403172000006 ()
Conference
50th ESLAB Symposium, MAR 14-18, 2016, Leiden, NETHERLANDS
Funder
Swedish National Space Board, 109/12, 135/13, 166/14, 114/13Swedish Research Council, 621-2013-4191, 621-2014-5526
Available from: 2017-09-08 Created: 2017-09-08 Last updated: 2017-09-08Bibliographically approved
Cowley, S. W., Zarka, P., Provan, G., Lamy, L. & Andrews, D. J. (2016). Comment on "A new approach to Saturn's periodicities" by J. F. Carbary. Journal of Geophysical Research - Space Physics, 121(3), 2418-2422
Open this publication in new window or tab >>Comment on "A new approach to Saturn's periodicities" by J. F. Carbary
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2016 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 121, no 3, p. 2418-2422Article in journal, Editorial material (Other academic) Published
Keywords
Saturn's magnetosphere
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-299393 (URN)10.1002/2015JA021996 (DOI)000374730900039 ()
Available from: 2016-07-18 Created: 2016-07-18 Last updated: 2017-11-28Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-7933-0322

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