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Kim, K., Edberg, N. J. T., Wahlund, J.-E. & Vigren, E. (2024). Alfvén Wing-Like Structures in Titan's Magnetotail During T122-T126 Flybys. Journal of Geophysical Research - Space Physics, 129(6), Article ID e2023JA032265.
Open this publication in new window or tab >>Alfvén Wing-Like Structures in Titan's Magnetotail During T122-T126 Flybys
2024 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 129, no 6, article id e2023JA032265Article in journal (Refereed) Published
Abstract [en]

In this paper, we study Titan's magnetotail using Cassini data from the T122-T126 flybys. These consecutive flybys had a similar flyby geometry and occurred at similar Saturn magnetospheric conditions, enabling an analysis of the magnetotail's structure. Using measurements from Cassini's magnetometer (MAG) and Radio and Plasma Wave System/Langmuir probe (RPWS/LP) we identify several features consistent with reported findings from earlier flybys, for example, T9, T63 and T75. We find that the so-called ’split’ signature of the magnetotail becomes more prominent at distances of at least 3,260 km (1.3 RT) downstream of Titan. We also identify a specific signature of the sub-alfvenic interaction of Titan with Saturn, the Alfvén wings, which are observed during the T123 and T124 flyby. A coordinate transformation is applied to mitigate variations in the upstream magnetic field, and all the flybys are projected into a new reference frame—aligned to the background magnetic field reference frame (BFA). We show that Titan's magnetotail is confined to a narrow region of around ∼4 RT YBFA. Finally, we analyze the general draping pattern in Titan's magnetotail throughout the TA to T126 flybys.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2024
Keywords
Titan, magnetotail, alfven wing, plasma
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-533017 (URN)10.1029/2023JA032265 (DOI)001241265300001 ()
Funder
Swedish Research Council, 2020-03962Swedish National Space Board
Available from: 2024-06-26 Created: 2024-06-26 Last updated: 2024-06-26Bibliographically approved
De Keyser, J., Edberg, N. J. T., Henri, P., Auster, H.-U. -., Galand, M., Rubin, M., . . . Van Dammep, C. C. (2024). In situ plasma and neutral gas observation time windows during a comet flyby: Application to the Comet Interceptor mission. Planetary and Space Science, 244, Article ID 105878.
Open this publication in new window or tab >>In situ plasma and neutral gas observation time windows during a comet flyby: Application to the Comet Interceptor mission
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2024 (English)In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 244, article id 105878Article in journal (Refereed) Published
Abstract [en]

A comet flyby, like the one planned for ESA's Comet Interceptor mission, places stringent requirements on spacecraft resources. To plan the time line of in situ plasma and neutral gas observations during the flyby, the size of the comet magnetosphere and neutral coma must be estimated well. For given solar irradiance and solar wind conditions, comet composition, and neutral gas expansion speed, the size of gas coma and magnetosphere during the flyby can be estimated from the gas production rate and the flyby geometry. Combined with flyby velocity, the time spent in these regions can be inferred and a data acquisition plan can be elaborated for each instrument, compatible with the limited data storage capacity. The sizes of magnetosphere and gas coma are found from a statistical analysis based on the probability distributions of gas production rate, flyby velocity, and solar wind conditions. The size of the magnetosphere as measured by bow shock standoff distance is 105-106 km near 1 au in the unlikely case of a Halley-type target comet, down to a nonexistent bow shock for targets with low activity. This translates into durations up to 103-104 seconds. These estimates can be narrowed down when a target is identified far from the Sun, and even more so as its activity can be predicted more reliably closer to the Sun. Plasma and neutral gas instruments on the Comet Interceptor main spacecraft can monitor the entire flyby by using an adaptive data acquisition strategy in the context of a record-and-playback scenario. For probes released from the main spacecraft, the inter-satellite communication link limits the data return. For a slow flyby of an active comet, the probes may not yet be released during the inbound bow shock crossing.

Place, publisher, year, edition, pages
Elsevier, 2024
Keywords
Comet plasma, Comet bow shock, In situ plasma measurements, Multi-point measurements, Comet Interceptor
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-527641 (URN)10.1016/j.pss.2024.105878 (DOI)001206636800001 ()
Available from: 2024-05-06 Created: 2024-05-06 Last updated: 2024-05-06Bibliographically approved
Edberg, N. J. T., Eriksson, A. I., Vigren, E., Nilsson, H., Gunell, H., Götz, C., . . . De Keyser, J. (2024). Scale size of cometary bow shocks. Astronomy and Astrophysics, 682, Article ID A51.
Open this publication in new window or tab >>Scale size of cometary bow shocks
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2024 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 682, article id A51Article in journal (Refereed) Published
Abstract [en]

Context. In past decades, several spacecraft have visited comets to investigate their plasma environments. In the coming years, Comet Interceptor will make yet another attempt. This time, the target comet and its outgassing activity are unknown and may not be known before the spacecraft has been launched into its parking orbit, where it will await a possible interception. If the approximate outgassing rate can be estimated remotely when a target has been identified, it is desirable to also be able to estimate the scale size of the plasma environment, defined here as the region bound by the bow shock.

Aims. This study aims to combine previous measurements and simulations of cometary bow shock locations to gain a better understanding of how the scale size of cometary plasma environments varies. We compare these data with models of the bow shock size, and we furthermore provide an outgassing rate-dependent shape model of the bow shock. We then use this to predict a range of times and cometocentric distances for the crossing of the bow shock by Comet Interceptor, together with expected plasma density measurements along the spacecraft track.

Methods. We used data of the location of cometary bow shocks from previous spacecraft missions, together with simulation results from previously published studies. We compared these results with an existing model of the bow shock stand-off distance and expand on this to provide a shape model of cometary bow shocks. The model in particular includes the cometary outgassing rate, but also upstream solar wind conditions, ionisation rates, and the neutral flow velocity.

Results. The agreement between the gas-dynamic model and the data and simulation results is good in terms of the stand-off distance of the bow shock as a function of the outgassing rate. For outgassing rates in the range of 1027–1031–s-1, the scale size of cometary bow shocks can vary by four orders of magnitude, from about 102 km to 106 km, for an ionisation rate, flow velocity, and upstream solar wind conditions typical of those at 1 AU. The proposed bow shock shape model shows that a comet plasma environment can range in scale size from the plasma environment of Mars to about half of that of Saturn.

Conclusions. The model-data agreement allows for the planning of upcoming spacecraft comet encounters, such as that of Comet Interceptor, when a target has been identified and its outgassing rate is determined. We conclude that the time a spacecraft can spend within the plasma environment during a flyby can range from minutes to days, depending on the comet that is visited and on the flyby speed. However, to capture most of the comet plasma environment, including pick-up ions and upstream plasma waves, and to ensure the highest possible scientific return, measurements should still start well upstream of the expected bow shock location. From the plasma perspective, the selected target should preferably be an active comet with the lowest possible flyby velocity.

Place, publisher, year, edition, pages
EDP Sciences, 2024
Keywords
comets: general, plasmas
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-525518 (URN)10.1051/0004-6361/202346566 (DOI)001163661400003 ()
Funder
Swedish Research Council, 2020-03962
Available from: 2024-03-25 Created: 2024-03-25 Last updated: 2024-03-25Bibliographically approved
Jones, G. H., Snodgrass, C., Tubiana, C., Kuppers, M., Kawakita, H., Lara, L. M., . . . Ji, H. (2024). The Comet Interceptor Mission. Space Science Reviews, 220(1), Article ID 9.
Open this publication in new window or tab >>The Comet Interceptor Mission
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2024 (English)In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 220, no 1, article id 9Article, review/survey (Refereed) Published
Abstract [en]

Here we describe the novel, multi-point Comet Interceptor mission. It is dedicated to the exploration of a little-processed long-period comet, possibly entering the inner Solar System for the first time, or to encounter an interstellar object originating at another star. The objectives of the mission are to address the following questions: What are the surface composition, shape, morphology, and structure of the target object? What is the composition of the gas and dust in the coma, its connection to the nucleus, and the nature of its interaction with the solar wind? The mission was proposed to the European Space Agency in 2018, and formally adopted by the agency in June 2022, for launch in 2029 together with the Ariel mission. Comet Interceptor will take advantage of the opportunity presented by ESA’s F-Class call for fast, flexible, low-cost missions to which it was proposed. The call required a launch to a halo orbit around the Sun-Earth L2 point. The mission can take advantage of this placement to wait for the discovery of a suitable comet reachable with its minimum ΔV capability of 600 ms−1. Comet Interceptor will be unique in encountering and studying, at a nominal closest approach distance of 1000 km, a comet that represents a near-pristine sample of material from the formation of the Solar System. It will also add a capability that no previous cometary mission has had, which is to deploy two sub-probes – B1, provided by the Japanese space agency, JAXA, and B2 – that will follow different trajectories through the coma. While the main probe passes at a nominal 1000 km distance, probes B1 and B2 will follow different chords through the coma at distances of 850 km and 400 km, respectively. The result will be unique, simultaneous, spatially resolved information of the 3-dimensional properties of the target comet and its interaction with the space environment. We present the mission’s science background leading to these objectives, as well as an overview of the scientific instruments, mission design, and schedule.

Place, publisher, year, edition, pages
Springer, 2024
Keywords
Comets, Spacecraft, Instruments - spaceborne and space research
National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics Aerospace Engineering
Identifiers
urn:nbn:se:uu:diva-528346 (URN)10.1007/s11214-023-01035-0 (DOI)001194889900001 ()38282745 (PubMedID)
Funder
Swedish National Space Board, 108/18Swedish National Space Board, 2021-00047EU, Horizon 2020, 802699EU, Horizon 2020, 101079231The European Space Agency (ESA), 4000136673/21/NL/IB/igThe European Space Agency (ESA), 3-17164/21/NL/GP/pbeAcademy of Finland, 1345115Academy of Finland, 1336546Academy of Finland, 325805Academy of Finland, 335595EU, Horizon Europe, 10051045
Available from: 2024-05-20 Created: 2024-05-20 Last updated: 2024-05-27Bibliographically approved
Vigren, E., Eriksson, A., Edberg, N. J. T. & Snodgrass, C. (2023). A potential aid in the target selection for the comet interceptor mission. Planetary and Space Science, 237, Article ID 105765.
Open this publication in new window or tab >>A potential aid in the target selection for the comet interceptor mission
2023 (English)In: Planetary and Space Science, ISSN 0032-0633, E-ISSN 1873-5088, Vol. 237, article id 105765Article in journal (Refereed) Published
Abstract [en]

The upcoming Comet Interceptor mission involves a parking phase around the Sun-Earth L2 point before transferring to intercept the orbit of a long period comet, interstellar object or a back-up target in the form of a short-period comet. The target is not certain to be known before the launch in 2029. During the parking phase there may thus arise a scenario wherein a decision needs to be taken of whether to go for a particular comet or whether to discard that option in the hope that a better target will appear within a reasonable time frame later on. We present an expectation value-based formalism that could aid in the associated decision making provided that outlined requirements for its implementation exist.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Comets, Solar system, Probability theory
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-514901 (URN)10.1016/j.pss.2023.105765 (DOI)001071302000001 ()
Funder
Swedish National Space Board, 202100047
Available from: 2023-10-31 Created: 2023-10-31 Last updated: 2023-10-31Bibliographically approved
Kim, K., Edberg, N. J. T., Shebanits, O., Wahlund, J.-E., Vigren, E. & Bertucci, C. (2023). On Current Sheets and Associated Density Spikes in Titan's Ionosphere as Seen From Cassini. Journal of Geophysical Research - Space Physics, 128(3)
Open this publication in new window or tab >>On Current Sheets and Associated Density Spikes in Titan's Ionosphere as Seen From Cassini
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2023 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 128, no 3Article in journal (Refereed) Published
Abstract [en]

The Cassini spacecraft made in-situ measurements of Titan's plasma environment during 126 close encounters between 2004 and 2017. Here we report on observations from the Radio and Plasma Waves System/Langmuir probe instrument (RPWS/LP) from which we have observed, primarily on the outbound leg, a localized increase of the electron density by up to 150 cm−3 with respect to the background. This feature, appearing as an electron density spike in the data, is found during 28 of the 126 flybys. The data from RPWS/LP, the electron spectrometer from the Cassini Plasma Spectrometer package , and the magnetometer is used to calculate electron densities and magnetic field characteristics. The location of these structures around Titan with respect to the nominal corotation direction and the sun direction is investigated. We find that the electron density spikes are primarily observed on the dayside and ramside of Titan. We also observe magnetic field signatures that could suggest the presence of current sheets in most cases. The density spikes are extended along the trajectory of the spacecraft with the horizontal scale of ∼537 ± 160 km and vertical scale ∼399 ± 163 km. We suggest that the density spikes are formed as a result of the current sheet formation.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2023
Keywords
Titan, Cassini, current sheets, Langmuir probe
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-501378 (URN)10.1029/2022JA031118 (DOI)000949118800001 ()
Funder
Swedish Research Council, 2020-03962Swedish National Space Board
Available from: 2023-05-08 Created: 2023-05-08 Last updated: 2023-05-08Bibliographically approved
Stergiopoulou, K., Jarvinen, R., Andrews, D. J., Edberg, N. J. T., Dimmock, A. P., Kallio, E., . . . Khotyaintsev, Y. V. (2023). Solar Orbiter Model-Data Comparison in Venus' Induced Magnetotail. Journal of Geophysical Research - Space Physics, 128(2)
Open this publication in new window or tab >>Solar Orbiter Model-Data Comparison in Venus' Induced Magnetotail
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2023 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 128, no 2Article in journal (Refereed) Submitted
Abstract [en]

We investigate the structure of the Venusian magnetotail utilizing magnetic field and electron density measurements that cover a wide range of distances from the planet, from the first two Solar Orbiter Venus flybys. We examine the magnetic field components along the spacecraft trajectory up to 80 Venus radii down the tail. Even though the magnetic field behavior differs considerably between the two cases, we see extended electron density enhancements covering distances greater than ∼20 RV in both flybys. We compare the magnetic field measurements with a global hybrid model of the induced magnetosphere and magnetotail of Venus, to examine to what degree the observations can be understood with the simulation. The model upstream conditions are stationary and the solution encloses a large volume of 83 RV × 60 RV × 60 RV in which we look for spatial magnetic field and plasma variations. We rotate the simulation solution to describe different stationary upstream IMF clock angle cases with a 10° step and find the clock angle for which the agreement between observations and model is maximized along Solar Orbiter's trajectory in 1-min steps. We find that in both flybys there is better agreement with the observations when we rotate the model for some intervals, while there are parts that cannot be well reproduced by the model irrespective of how we vary the IMF clock angle, suggesting the presence of non-stationary features in  the Venus-solar wind interaction not accounted for in the hybrid model.

Place, publisher, year, edition, pages
American Geophysical Union (AGU), 2023
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-481216 (URN)10.1029/2022JA031023 (DOI)000949130300001 ()
Available from: 2022-08-06 Created: 2022-08-06 Last updated: 2023-04-19Bibliographically approved
Burne, S., Bertucci, C., Sergis, N., Morales, L. F., Achilleos, N., Sanchez-Cano, B., . . . Kurth, B. S. (2023). Space Weather in the Saturn-Titan System. Astrophysical Journal, 948(1), Article ID 37.
Open this publication in new window or tab >>Space Weather in the Saturn-Titan System
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2023 (English)In: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 948, no 1, article id 37Article in journal (Refereed) Published
Abstract [en]

New evidence based on Cassini magnetic field and plasma data has revealed that the discovery of Titan outside Saturn's magnetosphere during the T96 flyby on 2013 December 1 was the result of the impact of two consecutive interplanetary coronal mass ejections (ICMEs) that left the Sun in 2013 early November and interacted with the moon and the planet. We study the dynamic evolution of Saturn's magnetopause and bow shock, which evidences a magnetospheric compression from late November 28 to December 4 (at least), under prevailing solar wind dynamic pressures of 0.16-0.3 nPa. During this interval, transient disturbances associated with the two ICMEs are observed, allowing for the identification of their magnetic structures. By analyzing the magnetic field direction, and the pressure balance in Titan's induced magnetosphere, we show that Cassini finds Saturn's moon embedded in the second ICME after being swept by its interplanetary shock and amid a shower of solar energetic particles that may have caused dramatic changes in the moon's lower ionosphere. Analyzing a list of Saturn's bow shock crossings during 2004-2016, we find that the magnetospheric compression needed for Titan to be in the supersonic solar wind can be generally associated with the presence of an ICME or a corotating interaction region. This leads to the conclusion that Titan would rarely face the pristine solar wind, but would rather interact with transient solar structures under extreme space weather conditions.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP)IOP Publishing Ltd, 2023
National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-502678 (URN)10.3847/1538-4357/acc738 (DOI)000981230600001 ()
Available from: 2023-05-29 Created: 2023-05-29 Last updated: 2024-01-15Bibliographically approved
Stergiopoulou, K., Andrews, D. J., Edberg, N. J. T., Halekas, J., Lester, M., Sanchez-Cano, B., . . . Gruesbeck, J. R. (2022). A Two-Spacecraft Study of Mars' Induced Magnetosphere's Response to Upstream Conditions. Journal of Geophysical Research - Space Physics, 127(4), Article ID e2021JA030227.
Open this publication in new window or tab >>A Two-Spacecraft Study of Mars' Induced Magnetosphere's Response to Upstream Conditions
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2022 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 127, no 4, article id e2021JA030227Article in journal (Refereed) Published
Abstract [en]

This is a two-spacecraft study, in which we investigate the effects of the upstream solar wind conditions on the Martian induced magnetosphere and upper ionosphere. We use Mars Express (MEX) magnetic field magnitude data together with interplanetary magnetic field (IMF), solar wind density, and velocity measurements from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, from November 2014 to November 2018. We compare simultaneous observations of the magnetic field magnitude in the induced magnetosphere of Mars (|B|(IM)) with the IMF magnitude (|B|(IMF)), and we examine variations in the ratio |B|(IM)/|B|(IMF) with solar wind dynamic pressure, speed and density. We find that the |B|(IM)/|B|(IMF) ratio in the induced magnetosphere generally decreases with increased dynamic pressure and that a more structured interaction is seen when comparing induced fields to the instantaneous IMF, where reductions in the relative fields at the magnetic pile up boundary (MPB) are more evident than in the field strength itself, along with enhancements in the immediate vicinity of the optical shadow of Mars. We interpret these results as evidence that while the induced magnetosphere is indeed compressed and induced field strengths are higher during periods of high dynamic pressure, a relatively larger amount of magnetic flux threads the region compared to that available from the unperturbed IMF during low dynamic pressure intervals.

Place, publisher, year, edition, pages
American Geophysical Union (AGU)American Geophysical Union (AGU), 2022
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-473189 (URN)10.1029/2021JA030227 (DOI)000778129500001 ()
Funder
Swedish National Space Board, DNR 156/16Swedish National Space Board, 162/14
Available from: 2022-04-27 Created: 2022-04-27 Last updated: 2024-01-15Bibliographically approved
Johansson, F., Vigren, E., Waite, J. H., Miller, K., Eriksson, A., Edberg, N. J. T. & Dreyer, J. (2022). Implications from secondary emission from neutral impact on Cassini plasma and dust measurements. Monthly notices of the Royal Astronomical Society, 515(2), 2340-2350
Open this publication in new window or tab >>Implications from secondary emission from neutral impact on Cassini plasma and dust measurements
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2022 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 515, no 2, p. 2340-2350Article in journal (Refereed) Published
Abstract [en]

We investigate the role of secondary electron and ion emission from impact of gas molecules on the Cassini Langmuir probe (RPWS-LP or LP) measurements in the ionosphere of Saturn. We add a model of the emission currents, based on laboratory measurements and data from comet 1P/Halley, to the equations used to derive plasma parameters from LP bias voltage sweeps. Reanalysing several hundred sweeps from the Cassini Grand Finale orbits, we find reasonable explanations for three open conundrums from previous LP studies of the Saturn ionosphere. We find an explanation for the observed positive charging of the Cassini spacecraft, the possibly overestimated ionospheric electron temperatures, and the excess ion current reported. For the sweeps analysed in detail, we do not find (indirect or direct) evidence of dust having a significant charge-carrying role in Saturn's ionosphere. We also produce an estimate of H2O number density from the last six revolutions of Cassini through Saturn's ionosphere in greater detail than reported by the Ion and Neutral Mass Spectrometer. Our analysis reveals an ionosphere that is highly structured in latitude across all six final revolutions, with mixing ratios varying with two orders of magnitude in latitude and one order of magnitude between revolutions and altitude. The result is generally consistent with an empirical photochemistry model balancing the production of H+ ions with the H+ loss through charge transfer with e.g. H2O, CH4, and CO2, for which water vapour appears as the likeliest dominant source of the signal in terms of yield and concentration.

Place, publisher, year, edition, pages
Oxford University Press (OUP), 2022
Keywords
planets and satellites: atmospheres, plasmas, space vehicles: instruments, methods: data analysis, methods: observational
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-482038 (URN)10.1093/mnras/stac1856 (DOI)000834368400005 ()
Funder
Swedish National Space Board, 143/18
Available from: 2022-08-19 Created: 2022-08-19 Last updated: 2022-08-19Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-1261-7580

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