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Abstract
CONTEXT Collisions between cometary neutrals in the inner coma of a comet and cometary ions that have been picked up into the solar wind flow and return to the coma lead to the formation of a broad inner boundary known as a collisionopause. This boundary is produced by a combination of charge transfer and chemical reactions, both of which are important at the location of the collisionopause boundary. Four spacecraft measured ion densities and velocities in the inner region of comets, exploring the part of the coma where an ion-neutral collisionopause boundary is expected to form. AIMS The aims are to determine the dominant physics behind the formation of the ion-neutral collisionopause and to evaluate where this boundary has been observed by spacecraft. METHODS We evaluated observations from three spacecraft at four different comets to determine if a collisionopause boundary was observed based on the reported ion velocities. We compared the measured location of the ion-neutral collisionopause with measurements of the collision cross sections to evaluate whether chemistry or charge exchange are more important at the location where the collisionopause is observed. RESULTS Based on measurements of the cross sections for charge transfer and for chemical reactions, the boundary observed by Rosetta appears to be the location where chemistry becomes the more probable result of a collision between H2O and H2O+ than charge exchange. Comparisons with ion observations made by Deep Space 1 at 19P/Borrelly and Giotto at 1P/Halley and 26P/Grigg-Skjellerup show that similar boundaries were observed at 19P/Borrelly and 1P/Halley. The ion composition measurements made by Giotto at Halley confirm that chemistry becomes more important inside of this boundary and that electron-ion dissociative recombination is a driver for the reported ion pileup boundary.
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Affiliation(s)
- K E Mandt
- Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd., Laurel, MD 20723
| | - A Eriksson
- Swedish Institute of Space Physics, POB 537, SE-751 21, Uppsala, Sweden
| | - A Beth
- Department of Physics, Imperial College London, Prince Consort Road, London SW7 2AZ, United Kingdom
| | - M Galand
- Department of Physics, Imperial College London, Prince Consort Road, London SW7 2AZ, United Kingdom
| | - E Vigren
- Swedish Institute of Space Physics, POB 537, SE-751 21, Uppsala, Sweden
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Heritier KL, Altwegg K, Berthelier JJ, Beth A, Carr CM, De Keyser J, Eriksson AI, Fuselier SA, Galand M, Gombosi TI, Henri P, Johansson FL, Nilsson H, Rubin M, Simon Wedlund C, Taylor MGGT, Vigren E. On the origin of molecular oxygen in cometary comae. Nat Commun 2018; 9:2580. [PMID: 29968720 PMCID: PMC6030164 DOI: 10.1038/s41467-018-04972-5] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2017] [Accepted: 06/05/2018] [Indexed: 11/09/2022] Open
Affiliation(s)
- K L Heritier
- Department of Physics, Imperial College London, Prince Consort Road, London, SW7 2AZ, UK.
| | - K Altwegg
- Physikalisches Institut, University of Bern, Sidlerstrasse 5, 3012, Bern, Switzerland
| | | | - A Beth
- Department of Physics, Imperial College London, Prince Consort Road, London, SW7 2AZ, UK
| | - C M Carr
- Department of Physics, Imperial College London, Prince Consort Road, London, SW7 2AZ, UK
| | - J De Keyser
- BIRA-IASB, Royal Belgian Institute for Space Aeronomy, Ringlaan 3, Brussels, Belgium
| | - A I Eriksson
- Swedish Institute of Space Physics, Ångström Laboratory, Lägerhyddsvägen 1, 752 37, Uppsala, Sweden
| | - S A Fuselier
- Southwest Research Institute, P.O. Drawer 28510, San Antonio, TX, 78228-0510, USA.,University of Texas at San Antonio, San Antonio, TX, 78249, USA
| | - M Galand
- Department of Physics, Imperial College London, Prince Consort Road, London, SW7 2AZ, UK
| | - T I Gombosi
- Department of Atmospheric, Oceanic and Space Sciences, University of Michigan, Ann Arbor, MI, 48109, USA
| | - P Henri
- LPC2E, CNRS, 3 Avenue de la recherche scientifique, 45071, Orléans, France
| | - F L Johansson
- Swedish Institute of Space Physics, Ångström Laboratory, Lägerhyddsvägen 1, 752 37, Uppsala, Sweden
| | - H Nilsson
- Swedish Institute of Space Physics, P.O. Box 812, 981 28, Kiruna, Sweden
| | - M Rubin
- Physikalisches Institut, University of Bern, Sidlerstrasse 5, 3012, Bern, Switzerland
| | - C Simon Wedlund
- Department of Physics, University of Oslo, Sem Sælands vei 24, postbox 1048, 0317, Oslo, Norway
| | - M G G T Taylor
- European Space Agency, ESTEC, Keplerlaan 1, Noordwijk, 2200 AG, The Netherlands
| | - E Vigren
- LATMOS/IPSL-CNRS-UPMC-UVSQ, 94100, Saint-Maur, France
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3
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Wahlund JE, Morooka MW, Hadid LZ, Persoon AM, Farrell WM, Gurnett DA, Hospodarsky G, Kurth WS, Ye SY, Andrews DJ, Edberg NJT, Eriksson AI, Vigren E. In situ measurements of Saturn's ionosphere show that it is dynamic and interacts with the rings. Science 2017; 359:66-68. [PMID: 29229651 DOI: 10.1126/science.aao4134] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2017] [Accepted: 11/27/2017] [Indexed: 11/02/2022]
Abstract
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.
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Affiliation(s)
- J-E Wahlund
- Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden.
| | - M W Morooka
- Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden
| | - L Z Hadid
- Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden
| | - A M Persoon
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA
| | - W M Farrell
- Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
| | - D A Gurnett
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA
| | - G Hospodarsky
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA
| | - W S Kurth
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA
| | - S-Y Ye
- Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242, USA
| | - D J Andrews
- Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden
| | - N J T Edberg
- Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden
| | - A I Eriksson
- Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden
| | - E Vigren
- Swedish Institute of Space Physics, Box 537, SE-751 21 Uppsala, Sweden
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Abstract
Previous modeling studies of Titan's dayside ionosphere predict electron number densities that are roughly a factor of 2 higher than those observed by the RPWS/Langmuir probe. The issue can equivalently be described as the ratio between the calculated electron production rates and the square of the observed electron number densities resulting in roughly a factor of 4 higher effective recombination coefficient than expected from the ion composition and the electron temperature. Here we make an extended reassessment of Titan's dayside ionization balance, focusing on 34 flybys between TA and T120. Using a recalibrated data set and by taking the presence of negative ions into account, we arrive at lower effective recombination coefficients compared with earlier studies. The values are still higher than expected from the ion composition and the electron temperature, but by a factor of ~2-3 instead of a factor of ~4. We have also investigated whether the derived effective recombination coefficients display dependencies on the solar zenith angle (SZA), the integrated solar EUV intensity (<80 nm), and the corotational plasma ram direction (RAM), and found statistically significant trends, which may be explained by a declining photoionization against the background ionization by magnetospheric particles (trends in SZA and RAM) and altered photochemistry (trend in EUV). We find that a series of flybys that occurred during solar minimum (2008) and with similar flyby geometries are associated with enhanced values of the effective recombination coefficient compared with the remaining data set, which also suggests a chemistry dependence on the sunlight conditions.
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Affiliation(s)
- O Shebanits
- Swedish Institute of Space Physics, Uppsala, Sweden
- Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
| | - E Vigren
- Swedish Institute of Space Physics, Uppsala, Sweden
| | - J-E Wahlund
- Swedish Institute of Space Physics, Uppsala, Sweden
| | - N J T Edberg
- Swedish Institute of Space Physics, Uppsala, Sweden
| | - J Cui
- School of Atmospheric Sciences, Sun Yat-Sen University, Zhuhai, Guangdong, China
| | - K E Mandt
- Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, TX, USA
- Space Science and Engineering Division, Southwest Research Institute, San Antonio, TX, USA
| | - J H Waite
- Space Science and Engineering Division, Southwest Research Institute, San Antonio, TX, USA
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Shebanits O, Vigren E, Wahlund JE, Holmberg MKG, Morooka M, Edberg NJT, Mandt KE, Waite JH. Titan's ionosphere: A survey of solar EUV influences. J Geophys Res Space Phys 2017; 122:7491-7503. [PMID: 31106105 PMCID: PMC6525010 DOI: 10.1002/2017ja023987] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Effects of solar EUV on positive ions and heavy negative charge carriers (molecular ions, aerosol, and/or dust) in Titan's ionosphere are studied over the course of almost 12 years, including 78 flybys below 1400 km altitude between TA (October 2004) and T120 (June 2016). The Radio and Plasma Wave Science/Langmuir Probe-measured ion charge densities (normalized by the solar zenith angle) show statistically significant variations with respect to the solar EUV flux. Dayside charge densities increase by a factor of ≈2 from solar minimum to maximum, while nightside charge densities are found to anticorrelate with the EUV flux and decrease by a factor of ≈3-4. The overall EUV dependence of the ion charge densities suggest inapplicability of the idealized Chapman theory below 1200 km in Titan's ionosphere. Nightside charge densities are also found to vary along Titan's orbit, with higher values in the sunward magnetosphere of Saturn compared to the magnetotail.
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Affiliation(s)
- O. Shebanits
- Swedish Institute of Space Physics, Uppsala, Sweden
- Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
| | - E. Vigren
- Swedish Institute of Space Physics, Uppsala, Sweden
| | | | - M. K. G. Holmberg
- Université de Toulouse, UPS-OMP, IRAP, Toulouse, France
- CNRS, IRAP, Toulouse, France
| | - M. Morooka
- Swedish Institute of Space Physics, Uppsala, Sweden
| | | | - K. E. Mandt
- Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, Texas, USA
- Space Science and Engineering Division, Southwest Research Institute, San Antonio, Texas, USA
| | - J. H. Waite
- Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, Texas, USA
- Space Science and Engineering Division, Southwest Research Institute, San Antonio, Texas, USA
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Shebanits O, Wahlund JE, Edberg NJT, Crary FJ, Wellbrock A, Andrews DJ, Vigren E, Desai RT, Coates AJ, Mandt KE, Waite JH. Ion and aerosol precursor densities in Titan's ionosphere: A multi-instrument case study. J Geophys Res Space Phys 2016; 121:10075-10090. [PMID: 31106104 PMCID: PMC6525009 DOI: 10.1002/2016ja022980] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
The importance of the heavy ions and dust grains for the chemistry and aerosol formation in Titan's ionosphere has been well established in the recent years of the Cassini mission. In this study we combine independent in situ plasma (Radio Plasma and Wave Science Langmuir Probe (RPWS/LP)) and particle (Cassini Plasma Science Electron Spectrometer, Cassini Plasma Science Ion Beam Spectrometer, and Ion and Neutral Mass Spectrometer) measurements of Titan's ionosphere for selected flybys (T16, T29, T40, and T56) to produce altitude profiles of mean ion masses including heavy ions and develop a Titan-specific method for detailed analysis of the RPWS/LP measurements (applicable to all flybys) to further constrain ion charge densities and produce the first empirical estimate of the average charge of negative ions and/or dust grains. Our results reveal the presence of an ion-ion (dusty) plasma below ~1100 km altitude, with charge densities exceeding the primary ionization peak densities by a factor ≥2 in the terminator and nightside ionosphere (n e /n i ≤ 0.1). We suggest that ion-ion (dusty) plasma may also be present in the dayside ionosphere below 900 km (n e /n i < 0.5 at 1000 km altitude). The average charge of the dust grains (≥1000 amu) is estimated to be between -2.5 and -1.5 elementary charges, increasing toward lower altitudes.
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Affiliation(s)
- O. Shebanits
- Swedish Institute of Space Physics, Uppsala, Sweden
- Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
| | | | | | - F. J. Crary
- University of Colorado Boulder, Boulder, Colorado, USA
| | - A. Wellbrock
- Mullard Space Science Laboratory, University College London, London, UK
- Centre for Planetary Sciences, University College London/Birkbeck, London, UK
| | | | - E. Vigren
- Swedish Institute of Space Physics, Uppsala, Sweden
| | - R. T. Desai
- Mullard Space Science Laboratory, University College London, London, UK
- Centre for Planetary Sciences, University College London/Birkbeck, London, UK
| | - A. J. Coates
- Mullard Space Science Laboratory, University College London, London, UK
- Centre for Planetary Sciences, University College London/Birkbeck, London, UK
| | - K. E. Mandt
- Space Science and Engineering Division, Southwest Research Institute, San Antonio, Texas, USA
- Department of Physics and Astronomy, University of Texas at San Antonio, San Antonio, Texas, USA
| | - J. H. Waite
- Space Science and Engineering Division, Southwest Research Institute, San Antonio, Texas, USA
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Thomas RD, Kashperka I, Vigren E, Geppert WD, Hamberg M, Larsson M, af Ugglas M, Zhaunerchyk V. Dissociative recombination of CH4(+). J Phys Chem A 2013; 117:9999-10005. [PMID: 23651407 DOI: 10.1021/jp400353x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
CH4(+) is an important molecular ion in the astrochemistry of diffuse clouds, dense clouds, cometary comae, and planetary ionospheres. However, the rate of one of the common destruction mechanisms for molecular ions in these regions, dissociative recombination (DR), is somewhat uncertain. Here, we present absolute measurements for the DR of CH4(+) made using the heavy ion storage ring CRYRING in Stockholm, Sweden. From our collision-energy dependent cross-sections, we infer a thermal rate constant of k(Te) = 1.71(±0.02) × 10(–6)(Te/300)(−0.66(±0.02)) cm3 s(–1) over the region of electron temperatures 10 ≤ Te ≤ 1000 K. At low collision energies, we have measured the branching fractions of the DR products to be CH4 (0.00 ± 0.00); CH3 + H (0.18 ± 0.03); CH2 + 2H (0.51 ± 0.03); CH2 + H2 (0.06 ± 0.01); CH + H2 + H (0.23 ± 0.01); and CH + 2H2 (0.02 ± 0.01), indicating that two or more C–H bonds are broken in 80% of all collisions.
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Affiliation(s)
- Richard D Thomas
- Department of Physics, Stockholm University , Albanova University Center, SE-106 91 Stockholm, Sweden
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Zhaunerchyk V, Thomas RD, Geppert WD, Hamberg M, Kamińska M, Vigren E, Larsson M, Midey AJ, Viggiano AA. Dissociative recombination of OPCl+ and OPCl2+: pushing the upper mass limit at CRYRING. J Chem Phys 2008; 128:134308. [PMID: 18397065 DOI: 10.1063/1.2884924] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
The dissociative recombination of OPCl+ and OPCl2+ has been studied at the storage ring CRYRING. The rate constants as a function of electron temperature have been derived to be 7.63 x 10(-7)(Te/300)(-0.89) and >1.2 x 10(-6)(Te/300)(-1.22) cm3s(-1), respectively. The lower limit quoted for the latter rate constant reflects the experimental inability to detect all of the reaction products. The branching fractions from the reaction have been measured for OPCl+ at approximately 0 eV interaction energy and are determined to be N(O+P+Cl)=(16+/-7)%, N(O+PCl)=(16+/-3)% and N(OP+Cl)=(68+/-5)%. These values have been obtained assuming that the rearrangement channel forming P+ClO is negligible, and ab initio calculations using GAUSSIAN03 are presented for the ion structures and energetics to support such an assumption. Finally, the limitations to using heavy ion storage rings such as CRYRING for studies into the dissociative recombination of large singly charged molecular ions are discussed.
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Affiliation(s)
- V Zhaunerchyk
- Department of Physics, Albanova University Centre, Stockholm University, SE-106 91 Stockholm, Sweden.
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Zhaunerchyk V, Geppert WD, Vigren E, Hamberg M, Danielsson M, Larsson M, Thomas RD, Kaminska M, Osterdahl F. Dissociative recombination study of N3+: Cross section and branching fraction measurements. J Chem Phys 2007; 127:014305. [PMID: 17627344 DOI: 10.1063/1.2747601] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
We report an investigation into the dissociative recombination of the azide radical cation, N(3) (+). The reaction rate constant has been measured to be 6.47 x 10(-7) cm(3) s(-1) at room temperature. This value is smaller than those reported earlier for the ion-electron neutralization of N(3) (+) at nitrogen atmospheric pressure. A strong propensity to dissociate through the N(2)+N channel has been observed.
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Affiliation(s)
- V Zhaunerchyk
- Department of Physics, Albanova University Centre, Stockholm University, S10691 Stockholm, Sweden
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