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As Rosetta was orbiting comet 67P/Churyumov‐Gerasimenko, the Ion and Electron Sensor detected negative particles with angular distributions like those of the concurrently measured solar wind protons but with fluxes of only about 10% of the proton fluxes and energies of about 90% of the proton energies. Using well‐known cross sections and energy‐loss data, it is determined that the fluxes and energies of the negative particles are consistent with the production of H− ions in the solar wind by double charge exchange with molecules in the coma., Key Points Double charge exchange of protons produces negative H ions in the solar windThe measurements agree with published laboratory cross sections and energy deficitsThe cross sections and energy deficits are estimated for the first time in the space environment

Observations of the coma near the nucleus of comet 67P/Churyumov-Gerasimenko (67P) made by the IES (Ion and Electron Sensor) instrument onboard the Rosetta Orbiter during late 2014 showed that electron fluxes greatly exceeded solar wind electron fluxes. The IES is part of the Rosetta Plasma Consortium. This paper reports on electron energy spectra measured by IES near the nucleus as well as approximate densities and average energies for the suprathermal electrons when the comet was at a heliocentric distance of about 3 AU. Comparisons are made with electron densities measured by other instruments. The high electron densities observed (e.g., ne ≈ 10–100 cm−3) must be associated with the cometary ion density enhancement created mainly by the photoionization of cometary gas by solar radiation; there are other processes that also contribute. Quasineutrality requires that the electron and ion densities be the same, and under certain conditions an ambipolar electric field is required to achieve quasi-neutrality. We present the results of a test particle model of cometary ion pickup by the solar wind and a two-stream electron transport code and use these results to interpret the IES data. We also estimate the effects on the electron spectrum of a compression of the electron fluid parcel. The electrons detected by IES can have energies as high as about 100–200 eV near the comet on some occasions, in which case the hot electrons can significantly enhance ionization rates of neutrals via impact ionization.

onization of neutrals by precipitating electrons and ions is the main source of Titan's nightside ionosphere. This paper has two goals: (1) characterization of the role of electron impact ionization on the nightside ionosphere for different magnetospheric conditions and (2) presentation of empirical ion production rates determined using densities measured by the Cassini Ion and Neutral Mass Spectrometer on the nightside. The ionosphere between 1000 and 1400 km is emphasized. We adopt electron fluxes measured by the Cassini Plasma Spectrometer-Electron Spectrometer and the Magnetospheric Imaging Instrument as classified by Rymer et al. (2009). The current paper follows an earlier paper (Paper I), in which we investigated sources of Titan's dayside ionosphere and demonstrated that the photoionization process is well understood. The current paper (Paper II) demonstrates that modeled and empirical ionization rates on the nightside are in agreement with an electron precipitation source above 1100 km. Ion production rate profiles appropriate for different Saturnian magnetospheric conditions, as outlined by Rymer et al., are constructed for various magnetic field topologies. Empirical production rate profiles are generated for deep nightside flybys of Titan. The results also suggest that at lower altitudes (below 1100 km) another source, such as ion precipitation, is probably needed. Fil: Richard, M. S.. University of Kansas; Estados Unidos. Benedictine College; Estados Unidos Fil: Cravens, T. E.. University of Kansas; Estados Unidos Fil: Wylie, C.. University of Kansas; Estados Unidos Fil: Webb, D.. University of Kansas; Estados Unidos Fil: Chediak, Q.. University of Kansas; Estados Unidos Fil: Mandt, K.. Southwest Research Institute; Estados Unidos Fil: Waite Jr, J. H.. Southwest Research Institute; Estados Unidos Fil: Rymer, A.. University Johns Hopkins; Estados Unidos Fil: Bertucci, Cesar. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Wellbrock, A.. University College London; Reino Unido Fil: Windsor, A.. Benedictine College. Department of Physics and Astronomy; Estados Unidos Fil: Coates, A. J.. University College London; Reino Unido

We present Cassini Langmuir probe measurements of the highest electron number densities ever reported from the ionosphere of Titan. The measured density reached 4310 cm−3 during the T85 Titan flyby. This is at least 500 cm−3 higher than ever observed before and at least 50% above the average density for similar solar zenith angles. The peak of the ionospheric density is not reached on this flyby, making the maximum measured density a lower limit. During this flyby, we also report that an impacting coronal mass ejection (CME) leaves Titan in the magnetosheath of Saturn, where it is exposed to shocked solar wind plasma for at least 2 h 45 min. We suggest that the solar wind plasma in the magnetosheath during the CME conditions significantly modifies Titan's ionosphere by an addition of particle impact ionization by precipitating protons. Fil: Edberg, N. J. T.. Swedish Institute of Space Physics; Suecia Fil: Andrews, D. J.. Swedish Institute of Space Physics; Suecia Fil: Shebanits, O.. Swedish Institute of Space Physics; Suecia Fil: Agren, K.. Swedish Institute of Space Physics; Suecia Fil: Wahlund, J. E.. Swedish Institute of Space Physics; Suecia Fil: Opgenoorth, H. J.. Swedish Institute of Space Physics; Suecia Fil: Roussos, E.. Max Planck Institute for Solar System Research; Alemania Fil: Garnier, P.. University of Toulouse; Francia Fil: Cravens, T. E.. University of Kansas; Estados Unidos Fil: Badman, S. V.. University of Leicester; Reino Unido Fil: Modolo, R.. UVSQ/LATMOS-IPSL/CNRS-INSU; Francia Fil: Bertucci, Cesar. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Dougherty, M. K.. Imperial College London; Reino Unido

Plasma in Titan´s ionosphere flows in response to forcing from thermal pressure gradients, magnetic forces, gravity, and ion-neutral collisions. This paper takes an empirical approach to the ionospheric dynamics by using data from Cassini instruments to estimate pressures, flow speeds, and time constants on the dayside and nightside. The plasma flow speed relative to the neutral gas speed is approximately 1 m s‑1 near an altitude of 1000 km and 200 m s‑1 at 1500 km. For comparison, the thermospheric neutral wind speed is about 100 m s‑1. The ionospheric plasma is strongly coupled to the neutrals below an altitude of about 1300 km. Transport, vertical or horizontal, becomes more important than chemistry in controlling ionospheric densities above about 1200-1500 km, depending on the ion species. Empirical estimates are used to demonstrate that the structure of the ionospheric magnetic field is determined by plasma transport (including neutral wind effects) for altitudes above about 1000 km and by magnetic diffusion at lower altitudes. The paper suggests that a velocity shear layer near 1300 km could exist at some locations and could affect the structure of the magnetic field. Both Hall and polarization electric field terms in the magnetic induction equation are shown to be locally important in controlling the structure of Titan´s ionospheric magnetic field. Comparisons are made between the ionospheric dynamics at Titan and at Venus. Fil: Cravens, T. E.. University of Kansas; Estados Unidos Fil: Richard, M.. University of Kansas; Estados Unidos Fil: Ma, Y. J.. University of California; Estados Unidos Fil: Bertucci, Cesar. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Luhmann, J. G.. University of California; Estados Unidos Fil: Ledvina, S.. University of California; Estados Unidos Fil: Robertson, I. P.. University of Kansas; Estados Unidos Fil: Wahlund, J. E.. Swedish Institute of Space Physics; Suecia Fil: Ågren, K.. Swedish Institute of Space Physics; Suecia Fil: Cui, J.. Imperial College London; Reino Unido Fil: Muller Wodarg, I.. Imperial College London; Reino Unido Fil: Waite, J. H.. Southwest Research Institute; Estados Unidos Fil: Dougherty, M.. Imperial College London; Reino Unido Fil: Bell, J.. Southwest Research Institute; Estados Unidos Fil: Ulusen, D.. University of California; Estados Unidos

When the Cassini spacecraft flew by Titan on 13 June 2007, at 13.6 Saturn local time, Titan was directly observed to be outside Saturn′s magnetopause. Cassini observations showed dramatic changes of magnetic field orientation as well as other plasma flow parameters during the inbound and outbound segments. In this paper, we study Titan's ionospheric responses to such a sudden change in the upstream plasma conditions using a sophisticated multispecies global MHD model. Simulation results of three different cases (steady state, simple current sheet crossing, and magnetopause crossing) are presented and compared against Cassini Magnetometer, Langmuir Probe, and Cassini Plasma Spectrometer observations. The simulation results provide clear evidence for the existence of a fossil field that was induced in the ionosphere. The main interaction features, as observed by the Cassini spacecraft, are well reproduced by the time-dependent simulation cases. Simulation also reveals how the fossil field was trapped during the interaction and shows the coexistence of two pileup regions with opposite magnetic orientation, as well as the formation of a pair of new Alfven wings and tail disconnection during the magnetopause crossing process. Fil: Ma, Y. J.. University of California; Estados Unidos Fil: Russell, C. T.. University of California; Estados Unidos Fil: Nagy, A. F.. University of Michigan; Estados Unidos Fil: Toth, G.. University of Michigan; Estados Unidos Fil: Bertucci, Cesar. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina Fil: Dougherty, M. K.. Imperial College London; Reino Unido Fil: Neubauer, F. M.. University of Cologne; Alemania Fil: Wellbrock, A.. University College London; Estados Unidos Fil: Coates, A. J.. University College London; Estados Unidos Fil: Garnier, P.. Swedish Institute of Space Physics; Suecia Fil: Wahlund, J. E.. Swedish Institute of Space Physics; Suecia Fil: Cravens, T. E.. University of Kansas; Estados Unidos Fil: Crary, F. J.. Southwest Research Institute; Estados Unidos

International audience; We present our analysis of the diurnal variations of Titan's ionosphere (between 1000 and 1300 km) based on a sample of Ion Neutral Mass Spectrometer (INMS) measurements in the Open Source Ion (OSI) mode obtained from eight close encounters of the Cassini spacecraft with Titan. Although there is an overall ion depletion well beyond the terminator, the ion content on Titan's nightside is still appreciable, with a density plateau of ~700 cm−3 below ~1300 km. Such a plateau is a combined result of significant depletion of light ions and modest depletion of heavy ones on Titan's nightside. We propose that the distinctions between the diurnal variations of light and heavy ions are associated with their different chemical loss pathways, with the former primarily through “fast” ion-neutral chemistry and the latter through “slow” electron dissociative recombination. The strong correlation between the observed night-to-day ion density ratios and the associated ion lifetimes suggests a scenario in which the ions created on Titan's dayside may survive well to the nightside. The observed asymmetry between the dawn and dusk ion density profiles also supports such an interpretation. We construct a time-dependent ion chemistry model to investigate the effect of ion survival associated with solid body rotation alone as well as superrotating horizontal winds. For long-lived ions, the predicted diurnal variations have similar general characteristics to those observed. However, for short-lived ions, the model densities on the nightside are significantly lower than the observed values. This implies that electron precipitation from Saturn's magnetosphere may be an additional and important contributor to the densities of the short-lived ions observed on Titan's nightside.

Solar extreme ultraviolet and x-ray radiation and energetic plasma from Saturn's magnetosphere interact with the upper atmosphere producing an ionosphere at Titan. The highly coupled ionosphere and upper atmosphere system mediates the interaction between Titan and the external environment. New insights into Titan's ionosphere are being facilitated by data from several instruments onboard the Cassini Orbiter, although the Ion and Neutral Mass Spectrometer (INMS) measurements will be emphasized in this talk. Measurements and comparisons with a model will be discussed for both the day and night on Titan. Electron impact ionization associated with precipitation of magnetospheric electrons (measured by the electron sensor on the CAPS spectrometer) seems the likely explanation for the nightside ionosphere but photoionization by solar radiation is the dominant source on the dayside. In this talk we will emphasize possible explanations for the temporal and/or spatial structure observed by the INMS and RPWS/LP (Radio and Plasma Wave – Langmuir probe) experiments during the T5 nightside pass, suggesting that temporal changes in the incident magnetospheric electron flux might be responsible for much of this structure.

We present the results of two XMM-Newton observations of Jupiter carried out in 2003 for 100 and 250 ks (or 3 and 7 planet rotations) respectively. X-ray images from the EPIC CCD cameras show prominent emission from the auroral regions in the 0.2 - 2.0 keV band: the spectra are well modelled by a combination of emission lines, including most prominently those of highly ionised oxygen (OVII and OVIII). In addition, and for the first time, XMM-Newton reveals the presence in both aurorae of a higher energy component (3 - 7 keV) which is well described by an electron bremsstrahlung spectrum. This component is found to be variable in flux and spectral shape during the Nov. 2003 observation, which corresponded to an extended period of intense solar activity. Emission from the equatorial regions of Jupiter's disk is also observed, with a spectrum consistent with that of solar X-rays scattered in the planet's upper atmosphere. Jupiter's X-rays are spectrally resolved with the RGS which clearly separates the prominent OVII contribution of the aurorae from the OVIII, FeXVII and MgXI lines, originating in the low-latitude disk regions of the planet., 6 pages, 11 figures, Proceedings of the Symposium 'The X-ray Universe 2005', San Lorenzo de El Escorial, Spain, 26-30 September 2005. In press

International audience

As Rosetta was orbiting comet 67P/Churyumov-Gerasimenko, the Ion and Electron Sensor detected negative particles with angular distributions like those of the concurrently measured solar wind protons but with fluxes of only about 10% of the proton fluxes and energies of about 90% of the proton energies. Using well-known cross sections and energy-loss data, it is determined that the fluxes and energies of the negative particles are consistent with the production of H- ions in the solar wind by double charge exchange with molecules in the coma.