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)

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

Comparison of the ionospheres of Venus, Mars, and Titan: ionospheric photoelectrons A.J.Coates 1, S.M.E.Tsang 1, A. Wellbrock 1, R.A.Frahm 2, J.D.Winningham 2, S.Barabash 3, R.Lundin 3, D.T.Young 2, F.Crary 2, Mullard Space Science Laboratory, UCL, UK Southwest Research Institite, Texas, USA IRF-Kiruna, Sweden and the CAPS and ASPERA-3 and 4 teams

Photoionisation major source on day side of planetary ionospheres – produces photoelectrons Solar spectrum gives energies – expect electron peaks at , 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

Sensor Reference MeasuresEnergy range (eV/q) Energy resolution (  E/E, %) Angle range (  ) Angle bin (  ) GEOS-1, 2 S-302 Suprathermal Plasma Analyser Wrenn et al., 1981 Energy and direction , 8018x18, 8x32 CAPS Electron spectrometer (ELS) Linder et al., 1998, Young et al, 2004 Energy and direction , x520x5 ASPERA-3 ELS Barabash et al., 2007a Energy and direction 10-20, x422.5x4 ASPERA-4 ELS Barabash et al., 2007b Energy and direction 1-30, x422.5x4 CAPS, ASPERA-ELS can measure ionospheric photoelectron spectrum at Titan, Mars, Venus

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

Coates et al., (PSS submitted, 2009)

Mars Express – photoelectrons in tail Frahm et al, Icarus 06, Space Science Reviews 2007 Estimate for Mars photoelectron escape 3.14x10 23 s -1 (Frahm et al Icarus in press 2009) – preliminary - photoelectron drawn escape contributes?

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

Venus: solar wind interaction – 18 May 06 From Coates et al, PSS 2008 First observation in Venus ionosphere by VEX ASPERA-4 ELS From O rather than CO 2

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

Coates et al., (PSS submitted, 2009)

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 Titan - Ionospheric electrons in the tail: T9 encounter Ionospheric photoelectrons

CA In shadow photoelectrons Titan - T15: ELS spectrogram 2 Jul :15 UT – 10:15 UT Photoelectrons at altitudes up to 5760km (2.2R T ) Wellbrock et al 2009

Titan - T15 modelling results Sillanp ää 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 Titan Equatorial plane Corotation flow Spacecraft trajectory photoelectron region B field lines connected to photoelectron region Dayside ionosphere

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

Conclusions Photolectrons are a tracer of magnetic connection to ionosphere Similar process at all objects with ambipolar electric field enhancing outflow VenusEarthMarsTitan InteractionSolar wind Saturn magnetosphere MagnetizationNoYes - dipoleLocalisedNo Photoionization (dayside) CO 2, ON 2, O 2 CO 2 N2N2 TailYesMagnetosphereYes Related ion escape? SomePolar windSome