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  1. Summer student work at MSSL, 2009 • Kate Husband – investigation of magnetosheath electron distribution functions. Flat-topped PSD distributions, correlation with location within magnetosheath. Found wider flat top near shock. Related to cross shock potential. • Joe Whittingham – determination of spacecraft potentials for Vex mission up to 2009, using s/c photoelectrons (positive potential) and ionospheric photoelectrons (negative potential)

  2. Sharon Tsang • Working on photoelectrons in tail • Paper to be resubmitted very soon (JGR-planets) • Some progress on statistical study (update at AGU)

  3. Comparison of the ionospheres of Venus, Mars, and Titan: ionospheric photoelectrons A.J.Coates1, S.M.E.Tsang1, A. Wellbrock1, R.A.Frahm2, J.D.Winningham2, S.Barabash3, R.Lundin3, D.T.Young2, F.Crary2, Mullard Space Science Laboratory, UCL, UK Southwest Research Institite, Texas, USA IRF-Kiruna, Swedenand the CAPS and ASPERA-3 and 4 teams

  4. Photoionisation major source on day side of planetary ionospheres – produces photoelectrons • Solar spectrum gives energies – expect electron peaks at 21-24, 27 eV • Many measurements of photoelectrons in Earth ionosphere giving detailed spectra (e.g. Lee et al 1980), other models • A ‘fingerprint’ for day side ionosphere Mantas and Hansen, 1979

  5. CAPS, ASPERA-ELS can measure ionospheric photoelectron spectrum at Titan, Mars, Venus

  6. Earth: ionospheric photoelectrons reach magnetosphere Fluxes seen for SZA < 97 in the ionosphere at foot of modelled Earth magnetic field Ionospheric photoelectrons in Earth’s magnetosphere up to 6.6 Re (Coates et al, 1985) • Magnetic connection from sunlit ionosphere to spacecraft • Provides non-thermal escape mechanism – electric field set up (polar wind)

  7. Coates et al., (PSS submitted, 2009)

  8. Mars Express – photoelectrons in tail Frahm et al, Icarus 06, Space Science Reviews 2007 Estimate for Mars photoelectron escape 3.14x1023 s-1 (Frahm et al Icarus in press 2009) – preliminary - photoelectron drawn escape contributes?

  9. Liemohn et al (2006, Icarus, Space Sci Rev) modelled photoelectron paths

  10. First observation in Venus ionosphere by VEX ASPERA-4 ELS • From O rather than CO2 Venus: solar wind interaction – 18 May 06 From Coates et al, PSS 2008

  11. D C C D Venus – ionospheric photoelectrons seen in tail as well as day side (Tsang et al, 2009, submitted)

  12. Coates et al., (PSS submitted, 2009)

  13. Titan - Ionospheric electrons in the tail: T9 encounter • Interval 1 – evidence of ionospheric plasma escape & connection to sunlit ionosphere; heavy ions • Interval 2 – mixed ionospheric and magnetospheric plasma; light ions • Role of ambipolar electric field in escape – similar to Earth’s polar wind – and lower mass from higher altitude • Coates et al, 2007b, Coates 2009, Coates et al 2009 Ionospheric photoelectrons

  14. Titan - T15: ELS spectrogram 2 Jul 2006 8:15 UT – 10:15 UT In shadow CA photoelectrons • Photoelectrons at altitudes up to 5760km (2.2RT) • Wellbrock et al 2009

  15. Titan - T15 modelling results Spacecraft trajectory photoelectron region Equatorial plane Titan B field lines connected to photoelectron region Corotation flow Dayside ionosphere • Sillanpää et al hybrid model results indicate magnetic connections to the dayside ionosphere. • Only B field lines connected to observed photoelectron region (pink line) are shown. • The field lines connect to the sunlit ionosphere near the south pole

  16. Conclusions on ionospheric photoelectrons (IPE) • IPE are seen clearly in the dayside ionospheres with suitable instrumentation • The energy spectrum of IPE is distinctive, acting as a ‘fingerprint’ for ionisation processes • IPE can, at times, be seen at large distances from those ionospheres, e.g. in Earth’s magnetosphere, and in the tails of Mars, Venus and Titan • IPE are a sensitive diagnostic ‘tracer’ of a magnetic connection to the production location, namely the dayside ionospheres • IPE may play a role in setting up an electric field which would enhance ionospheric escape See Coates et al., PSS submitted, 2009 for further details

  17. Conclusions • Photolectrons are a tracer of magnetic connection to ionosphere • Similar process at all objects with ambipolar electric field enhancing outflow