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Xystouris, G., Arridge, C. S., Morooka, M. & Wahlund, J.-E. (2023). Estimating the optical depth of Saturn's main rings using the Cassini Langmuir Probe. Monthly notices of the Royal Astronomical Society, 526(4), 5839-5860
Open this publication in new window or tab >>Estimating the optical depth of Saturn's main rings using the Cassini Langmuir Probe
2023 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 526, no 4, p. 5839-5860Article in journal (Refereed) Published
Abstract [en]

A Langmuir Probe (LP) measures currents from incident charged particles as a function of the applied bias voltage. While onboard a spacecraft the particles are either originated from the surrounding plasma, or emitted (e.g. through photoemission) from the spacecraft itself. The obtained current-voltage curve reflects the properties of the plasma in which the probe is immersed into, but also any photoemission due to illumination of the probe surface: As photoemission releases photoelectrons into space surrounding the probe, these can be recollected and measured as an additional plasma population. This complicates the estimation of the properties of the ambient plasma around the spacecraft. The photoemission current is sensitive to the extreme ultraviolet (UV) part of the spectrum, and it varies with the illumination from the Sun and the properties of the LP surface material, and any variation in the photoelectrons irradiance can be measured as a change in the current voltage curve. Cassini was eclipsed multiple times by Saturn and the main rings over its 14 yr mission. During each eclipse the LP recorded dramatic changes in the current-voltage curve, which were especially variable when Cassini was in shadow behind the main rings. We interpret these variations as the effect of spatial variations in the optical depth of the rings and hence use the observations to estimate the optical depth of Saturn's main rings. Our estimates are comparable with UV optical depth measurements from Cassini's remote sensing instruments.

Place, publisher, year, edition, pages
Oxford University Press, 2023
Keywords
opacity, plasmas, instrumentation: miscellaneous, eclipses, planets and satellites: rings
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-517521 (URN)10.1093/mnras/stad2793 (DOI)001092493900004 ()
Available from: 2023-12-13 Created: 2023-12-13 Last updated: 2023-12-13Bibliographically approved
Fletcher, L. N., Cavalié, T., Grassi, D., Hueso, R., Lara, L. M., Kaspi, Y., . . . Costa, M. (2023). Jupiter Science Enabled by ESA's Jupiter Icy Moons Explorer. Space Science Reviews, 219(7), Article ID 53.
Open this publication in new window or tab >>Jupiter Science Enabled by ESA's Jupiter Icy Moons Explorer
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2023 (English)In: Space Science Reviews, ISSN 0038-6308, E-ISSN 1572-9672, Vol. 219, no 7, article id 53Article, review/survey (Refereed) Published
Abstract [en]

ESA's Jupiter Icy Moons Explorer (JUICE) will provide a detailed investigation of the Jovian system in the 2030s, combining a suite of state-of-the-art instruments with an orbital tour tailored to maximise observing opportunities. We review the Jupiter science enabled by the JUICE mission, building on the legacy of discoveries from the Galileo, Cassini, and Juno missions, alongside ground- and space-based observatories. We focus on remote sensing of the climate, meteorology, and chemistry of the atmosphere and auroras from the cloud-forming weather layer, through the upper troposphere, into the stratosphere and ionosphere. The Jupiter orbital tour provides a wealth of opportunities for atmospheric and auroral science: global perspectives with its near-equatorial and inclined phases, sampling all phase angles from dayside to nightside, and investigating phenomena evolving on timescales from minutes to months. The remote sensing payload spans far-UV spectroscopy (50-210 nm), visible imaging (340-1080 nm), visible/near-infrared spectroscopy (0.49-5.56 & mu;m), and sub-millimetre sounding (near 530-625 GHz and 1067-1275 GHz). This is coupled to radio, stellar, and solar occultation opportunities to explore the atmosphere at high vertical resolution; and radio and plasma wave measurements of electric discharges in the Jovian atmosphere and auroras. Cross-disciplinary scientific investigations enable JUICE to explore coupling processes in giant planet atmospheres, to show how the atmosphere is connected to (i) the deep circulation and composition of the hydrogen-dominated interior; and (ii) to the currents and charged particle environments of the external magnetosphere. JUICE will provide a comprehensive characterisation of the atmosphere and auroras of this archetypal giant planet.

Place, publisher, year, edition, pages
Springer Nature, 2023
Keywords
JUICE, Jupiter, Atmospheres, Auroras, Dynamics, Chemistry
National Category
Astronomy, Astrophysics and Cosmology Fusion, Plasma and Space Physics Aerospace Engineering
Identifiers
urn:nbn:se:uu:diva-515388 (URN)10.1007/s11214-023-00996-6 (DOI)001072292500001 ()37744214 (PubMedID)
Funder
EU, Horizon 2020, 723890Swedish National Space Board
Available from: 2023-11-01 Created: 2023-11-01 Last updated: 2023-11-01Bibliographically 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
Shebanits, O., Wahlund, J.-E., Waite, J. H. & Dougherty, M. K. (2022). Conductivities of Titan's Dusty Ionosphere. Journal of Geophysical Research - Space Physics, 127(2), Article ID e2021JA029910.
Open this publication in new window or tab >>Conductivities of Titan's Dusty Ionosphere
2022 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 127, no 2, article id e2021JA029910Article in journal (Refereed) Published
Abstract [en]

Titan's ionosphere hosts a globally distributed non-trivial dusty ion-ion plasma, providing an environment for studies of dusty ionospheres that is in many aspects unique in our solar system. Thanks to the Cassini mission, Titan's ionosphere also features one of the largest dusty plasma data sets from 126 flybys of the moon over 13 years, from 2004 to 2017. Recent studies have shown that negatively charged dust dramatically alters the electric properties of plasmas, in particular planetary ionospheres. Utilizing the full plasma content of the moon's ionosphere (electrons, positive ions, and negative ions/dust grains), we derive the electric conductivities and define the conductive dynamo region. Our results show that using the full plasma content increases the Pedersen conductivities at similar to 1,100-1,200 km altitude by up to 35% compared to the estimates using only electron densities. The Hall conductivities are in general not affected but several cases indicate a reverse Hall effect at similar to 900 km altitude (closest approach) and below. The dayside conductivities are shown to be factor similar to 7-9 larger than on the nightside, owing to higher dayside plasma densities.

Place, publisher, year, edition, pages
American Geophysical Union (AGU)American Geophysical Union (AGU), 2022
Keywords
dusty plasma, ionosphere, conductivity, Titan, Cassini
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-472231 (URN)10.1029/2021JA029910 (DOI)000765721800031 ()
Available from: 2022-04-11 Created: 2022-04-11 Last updated: 2024-01-15Bibliographically approved
Vigren, E., Dreyer, J., Eriksson, A. I., Johansson, F. L., Morooka, M. & Wahlund, J.-E. (2022). Empirical Photochemical Modeling of Saturn's Ionization Balance Including Grain Charging. The Planetary Science Journal, 3(2), Article ID 49.
Open this publication in new window or tab >>Empirical Photochemical Modeling of Saturn's Ionization Balance Including Grain Charging
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2022 (English)In: The Planetary Science Journal, E-ISSN 2632-3338, Vol. 3, no 2, article id 49Article in journal (Refereed) Published
Abstract [en]

We present a semianalytical photochemical model of Saturn's near-equatorial ionosphere and adapt it to two regions (similar to 2200 and similar to 1700 km above the 1 bar level) probed during the inbound portion of Cassini's orbit 292 (2017 September 9). The model uses as input the measured concentrations of molecular hydrogen, hydrogen ion species, and free electrons, as well as the measured electron temperature. The output includes upper limits, or constraints, on the mixing ratios of two families of molecules, on ion concentrations, and on the attachment rates of electrons and ions onto dust grains. The model suggests mixing ratios of the two molecular families that, particularly near similar to 1700 km, differ notably from what independent measurements by the Ion Neutral Mass Spectrometer suggest. Possibly connected to this, the model suggests an electron-depleted plasma with a level of electron depletion of around 50%. This is in qualitative agreement with interpretations of Radio Plasma Wave Science/Langmuir Probe measurements, but an additional conundrum arises in the fact that a coherent photochemical equilibrium scenario then relies on a dust component with typical grain radii smaller than 3 angstrom.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2022
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-495353 (URN)10.3847/PSJ/ac4eee (DOI)000911845800001 ()
Funder
Swedish National Space Board
Available from: 2023-01-30 Created: 2023-01-30 Last updated: 2023-10-03Bibliographically approved
Sulaiman, A. H., Achilleos, N., Bertucci, C., Coates, A., Dougherty, M., Hadid, L., . . . Waite, J. H. (2022). Enceladus and Titan: emerging worlds of the Solar System. Experimental astronomy, 54(2-3), 849-876
Open this publication in new window or tab >>Enceladus and Titan: emerging worlds of the Solar System
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2022 (English)In: Experimental astronomy, ISSN 0922-6435, E-ISSN 1572-9508, Vol. 54, no 2-3, p. 849-876Article in journal (Refereed) Published
Abstract [en]

Some of the major discoveries of the recent Cassini-Huygens mission have put Titan and Enceladus firmly on the Solar System map. The mission has revolutionised our view of Solar System satellites, arguably matching their scientific importance with that of their host planet. While Cassini-Huygens has made big surprises in revealing Titan's organically rich environment and Enceladus' cryovolcanism, the mission's success naturally leads us to further probe these findings. We advocate the acknowledgement of Titan and Enceladus science as highly relevant to ESA's long-term roadmap, as logical follow-on to Cassini-Huygens. In this White Paper, we will outline important science questions regarding these satellites and identify the science themes we recommend ESA cover during the Voyage 2050 planning cycle. Addressing these science themes would make major advancements to the present knowledge we have about the Solar System, its formation, evolution, and likelihood that other habitable environments exist outside the Earth's biosphere.

Place, publisher, year, edition, pages
Springer Nature, 2022
Keywords
Titan, Enceladus, Voyage 2050
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-502312 (URN)10.1007/s10686-021-09810-z (DOI)000724648600001 ()
Available from: 2023-05-24 Created: 2023-05-24 Last updated: 2024-01-17Bibliographically approved
Dreyer, J., Vigren, E., Johansson, F., Shebanits, O., Morooka, M., Wahlund, J.-E., . . . Waite, J. H. (2022). Identifying Shadowing Signatures of C Ring Ringlets and Plateaus in Cassini Data from Saturn's Ionosphere. The Planetary Science Journal, 3(7), Article ID 168.
Open this publication in new window or tab >>Identifying Shadowing Signatures of C Ring Ringlets and Plateaus in Cassini Data from Saturn's Ionosphere
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2022 (English)In: The Planetary Science Journal, E-ISSN 2632-3338, Vol. 3, no 7, article id 168Article in journal (Refereed) Published
Abstract [en]

For orbits 288 and 292 of Cassini's Grand Finale, clear dips (sharp and narrow decreases) are visible in the H-2(+) densities measured by the Ion and Neutral Mass Spectrometer (INMS). In 2017, the southern hemisphere of Saturn was shadowed by its rings and the substructures within. Tracing a path of the solar photons through the ring plane to Cassini's position, we can identify regions in the ionosphere that were shadowed by the individual ringlets and plateaus (with increased optical depths) of Saturn's C ring. The calculated shadowed altitudes along Cassini's trajectory line up well with the dips in the H-2(+) data when adjusting the latter based on a detected evolving shift in the INMS timestamps since 2013, illustrating the potential for verification of instrument timings. We can further estimate the mean optical depths of the ringlets/plateaus by comparing the dips to inbound H-2(+) densities. Our results agree well with values derived from stellar occultation measurements. No clear dips are visible for orbits 283 and 287, whose periapsides were at higher altitudes. This can be attributed to the much longer chemical lifetime of H2+ at these higher altitudes, which in turn can be further used to estimate a lower limit for the flow speed along Cassini's trajectory. The resulting estimate of similar to 0.3 km s(-1) at an altitude of similar to 3400 km is in line with prior suggestions. Finally, the ringlet and plateau shadows are not associated with obvious dips in the electron density, which is expected due to their comparatively long chemical (recombination) lifetime.

Place, publisher, year, edition, pages
Institute of Physics (IOP), 2022
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-497057 (URN)10.3847/PSJ/ac7790 (DOI)000914478200001 ()
Funder
Swedish National Space Board, 143/18E. och K.G. Lennanders StipendiestiftelseSwedish National Space Board, Dnr 195/20
Available from: 2023-02-23 Created: 2023-02-23 Last updated: 2023-10-03Bibliographically approved
Fischer, G., Panchenko, M., Macher, W., Kasaba, Y., Misawa, H., Tokarz, M., . . . Wahlund, J.-E. (2021). Calibration of the JUICE RWI Antennas by Numerical Simulation. Radio Science, 56(11), Article ID e2021RS007309.
Open this publication in new window or tab >>Calibration of the JUICE RWI Antennas by Numerical Simulation
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2021 (English)In: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 56, no 11, article id e2021RS007309Article in journal (Refereed) Published
Abstract [en]

The reception properties of the Radio Wave Instrument (RWI) onboard JUICE (Jupiter Icy Moons Explorer) have been determined using numerical methods applied to a mesh-grid model of the spacecraft. The RWI is part of the RPWI (Radio and Plasma Wave Investigation) and consists of three perpendicular dipoles mounted on a long boom. We determined their effective lengths vectors and capacitive impedances of 8-9 pF. We also investigated the change in effective antenna angles as a function of solar panel rotation and calculated the directivity of the antennas at higher frequencies up to the maximum frequency of 45 MHz of the receiver. We found that the RWI dipoles can be used for direction-finding with an accuracy of 2 degrees up to a frequency of 1.5 MHz. Additionally we calculated the influence of strong pulses from the JUICE active radar on RPWI and found that they should do no harm to its sensors and receivers.

Place, publisher, year, edition, pages
American Geophysical Union (AGU)AMER GEOPHYSICAL UNION, 2021
Keywords
antenna calibration, JUICE, Radio Wave Instrument
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-461849 (URN)10.1029/2021RS007309 (DOI)000722461700003 ()
Funder
Swedish National Space Board
Available from: 2021-12-17 Created: 2021-12-17 Last updated: 2024-01-15Bibliographically approved
Dreyer, J., Vigren, E., Morooka, M., Wahlund, J.-E., Buchert, S. C., Johansson, F. L. & Waite, J. H. (2021). Constraining the Positive Ion Composition in Saturn's Lower Ionosphere with the Effective Recombination Coefficient. The Planetary Science Journal, 2(1), Article ID 39.
Open this publication in new window or tab >>Constraining the Positive Ion Composition in Saturn's Lower Ionosphere with the Effective Recombination Coefficient
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2021 (English)In: The Planetary Science Journal, E-ISSN 2632-3338, Vol. 2, no 1, article id 39Article in journal (Refereed) Published
Abstract [en]

The present study combines Radio and Plasma Wave Science/Langmuir Probe and Ion and Neutral Mass Spectrometer data from Cassini's last four orbits into Saturn's lower ionosphere to constrain the effective recombination coefficient α300 from measured number densities and electron temperatures at a reference electron temperature of 300 K. Previous studies have shown an influx of ring material causes a state of electron depletion due to grain charging, which will subsequently affect the ionospheric chemistry. The requirement to take grain charging into account limits the derivation of α300 to upper limits. Assuming photochemical equilibrium and using an established method to calculate the electron production rate, we derive upper limits for α300 of ≲ 3 × 10−7 cm3 s−1 for altitudes below 2000 km. This suggests that Saturn's ionospheric positive ions are dominated by species with low recombination rate coefficients like HCO+. An ionosphere dominated by water group ions or complex hydrocarbons, as previously suggested, is incompatible with this result, as these species have recombination rate coefficients > 5 × 10−7 cm3 s−1 at an electron temperature of 300 K.

Place, publisher, year, edition, pages
American Astronomical SocietyAmerican Astronomical Society, 2021
National Category
Fusion, Plasma and Space Physics
Identifiers
urn:nbn:se:uu:diva-458301 (URN)10.3847/psj/abd6e9 (DOI)000912867900001 ()
Funder
Swedish National Space Board, 143/18Swedish National Space Board, 168/15
Available from: 2021-11-08 Created: 2021-11-08 Last updated: 2024-01-15Bibliographically approved
Chatain, A., Wahlund, J.-E., Shebanits, O., Hadid, L. Z., Morooka, M., Edberg, N. J. T., . . . Carrasco, N. (2021). Re-Analysis of the Cassini RPWS/LP Data in Titan's Ionosphere: 1. Detection of Several Electron Populations. Journal of Geophysical Research - Space Physics, 126(8), Article ID e2020JA028412.
Open this publication in new window or tab >>Re-Analysis of the Cassini RPWS/LP Data in Titan's Ionosphere: 1. Detection of Several Electron Populations
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2021 (English)In: Journal of Geophysical Research - Space Physics, ISSN 2169-9380, E-ISSN 2169-9402, Vol. 126, no 8, article id e2020JA028412Article in journal (Refereed) Published
Abstract [en]

Current models of Titan's ionosphere have difficulties in explaining the observed electron density and/or temperature. In order to get new insights, we re-analyzed the data taken in the ionosphere of Titan by the Cassini Langmuir probe (LP), part of the Radio and Plasma Wave Science (RPWS) instrument. This is the first of two papers that present the new analysis method (current paper) and statistics on the whole data set. We suggest that between two and four electron populations are necessary to fit the data. Each population is defined by a potential, an electron density and an electron temperature and is easily visualized by a distinct peak in the second derivative of the electron current, which is physically related to the electron energy distribution function (Druyvesteyn method). The detected populations vary with solar illumination and altitude. We suggest that the four electron populations are due to photo-ionization, magnetospheric particles, dusty plasma and electron emission from the probe boom, respectively.

Place, publisher, year, edition, pages
American Geophysical Union (AGU)AMER GEOPHYSICAL UNION, 2021
Keywords
dusty plasma, electron populations, electron temperature, Langmuir probe, RPWS, Titan ionosphere
National Category
Fusion, Plasma and Space Physics Astronomy, Astrophysics and Cosmology
Identifiers
urn:nbn:se:uu:diva-456142 (URN)10.1029/2020JA028412 (DOI)000691018000024 ()
Funder
Swedish National Space BoardSwedish National Space Board, 135/13Swedish Research Council, 621-2013-4191EU, European Research Council, 636829
Available from: 2021-10-15 Created: 2021-10-15 Last updated: 2024-01-15Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-2107-5859

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