New results in polarimetry of planetary thermospheric emissions: Earth and Jovian cases.

1. New results in polarimetry of planetary thermospheric emissions: Earth and Jovian cases. M. Barthelemy (1), J. Lilensten (1), C. Simon (2), H. Lamy(2), G Gronoff (3), H. Menager (1), S. Miller (4), M. Lystrup (5), H. Rothkael (6), J. Moen (7). IPAG, France BIRA-IASB, Belgium NASA, Langley,VA, USA UCL, UK University of Colorado, USA Polish Space Research Center, Poland University in Oslo, Norway Workshop Meudon

2. Polarization processes • Impact polarization Polarization rate depends of: • Pitch angle distribution • Kind of particles • Energy • Depolarization processes as collisions. • Emission in an anisotropic region: for ex Electric field. Ex. Lyman alpha polarization rate by electron impact. Laboratory measurement (from James et al 1998). Workshop Meudon

3. Earth case: POLARLIS,or the measurement of the POLarization of the Oxygen thermospheric Red Line In Svalbard. • Photo-polarimeter: SPP at KHO in Longyearbyen (Svalbard) and at Hornsund . Channel 1: Photomultiplier. Red filter centered on 6300 A with a FHWM of 1 nm. Linear polarization analyser. One rotation of the analyser every 4.02 s. Channel 2: Same, without the polarization filter. Steerable Polarization Photometer (SPP) built at the Oslo University (UiO). It includes 2 channels and a pan-tilt unit. Aperture is 2°. Workshop Meudon

4. 17 jan 2007 late afternoon. From Lilensten et al. 2008. GRL Workshop Meudon

5. Reassessment • Error in calibration angles. Correction around 45° • New measurements at Hornsund (no light pollution) • Confirmation of the detection • But rates around 1% after data processing • Direction close to the vertical (difference was due to the pollution) • Compatible with Bommier et al. 2011 • Raw polarisation before depolarizing collisions: ~18% • Vertical ie //B • Barthelemy et al. submitted 2010. Workshop Meudon

6. Jovian case • H3+ emissions in the IR. • The emission process is different: No emission due to electronic impact because of the chemical process of formation, but… • Possibility to get alignment due the electric fields in the auroral region. 2 half nights observation for August 2008 at the UKIRT with the instrument UIST-IRPOL in the Long L band (3.6-4.2 µm). Barthelemy et al. 2010, submitted Workshop Meudon

7. Workshop Meudon

8. Seventh data set: I at 3.95µm q (Normalized Stokes parameter) u (Normalized Stokes parameter) p (%) (Debiaised) Θ (°) (ref is the slit direction) v (Normalized Stokes parameter) The polarization direction are difficult to interpret… Workshop Meudon

9. Interpretation: Conclusion and Perspectives Workshop Meudon

10. Jovian case. • Auroral UV emissions. • Lyman  , the most promising: • Very intense (100 kR) • Emission due to electrons and/or protons. Various polarization rate and direction with the energy. • Radiative transfer in a presence of magnetic field for an allowed transition. • Due to this, possible variation of the polarization rate along the line profile. Need for very high resolution. Workshop Meudon

11. Needed in a dream world • Spatial resolution around 100km2 • Width of the oval ~200km. • Spectral resolution • Lyman alpha width is 0.02 nm and it exists H2 lines in coincidence with H-Lyman alpha. • Typical lyman alpha filter width (~5nm) Some lines of H2 but faint compared to H-Lyman alpha • Polarimetric accuracy under 1% • Only in the night side (dayside emission can reach 10% of the auroral emission!) Workshop Meudon

12. Feasability • Flux (at Ly alpha) • Expected spatial resolution:100 km2 • 100 kR in the oval (i.e. 1e11 ph.cm-2.s-1 averaged in all directions). • Orbit : for example EJSM in resonance 2:1 with Europa i.e. around 106km for the centre of the planet i.e. 7.9 10-1 ph.cm-2.s-1 Need an effective area of the instrument of 12.5 cm2 on a basis of 10ph.s-1. pix-1 (with an efficiency of the optics of 0.05, this correspond to an aperture of 250cm2) Pb moving pieces!!! • With a “better” orbit (more flux) : example of JUNO. • Polar orbit. • Closest point 4000km • ~12000km above the oval. Workshop Meudon

13. Spectra/Lyman alpha filter • Interest of spectra: • H2 lines • No mixing between H2 and Lyman alpha lines if sufficient resolution. • But not enough flux considering EJSM orbits to get H2 lines. • And possible problem with the grating. Workshop Meudon

14. Optical solution? • Exemple: SMESE-Lyot like design (mirrors) From Auchere et al. 1st SMESE workshop. Workshop Meudon

15. Conclusions • Difficult design due to the short wavelength • But • Strong interest • Best solution? • Mission to the planet (EJSM; too late for Juno) VS • Space telescope • Rq: Saturn has Ly alpha aurora 10 times fainter. Workshop Meudon

16. Perspectives and needs. • Diversity of processes,diversity of emissions • Specific information for each line and planet. • Others examples : • O 8446 Å, O 1304 Å* (Earth, Venus, Mars) • Na I 5890 Å (Mercury)….in progress • Needs for the jovian case • Ab initio calculation of the link between H3+ lines polarization and the fields (E and/or B). • Lab experiment. • In EJSM frame: Difficult to have a Ly alpha polarimeter. H3+ measurement as combined measurements Workshop Meudon

17. Polarisation as a tool to study the Solar System and beyond COST proposal reference: oc-2010-2-8667 Hervé Lamy1 & Mathieu Barthélemy2 1 Belgian Institute for Space Aeronomy (BISA) 2 Institut de Planétologie et d’Astrophysique de Grenoble (IPAG) Workshop Meudon