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Surface composition of Europa?

Surface composition of Europa?. What can we learn from in situ measurements in the exosphere and ionosphere?. K. Altwegg, University of Bern. Elemental, isotopic and molecular composition of Europa’s surface (by SIMS technology, primary ions provided by Jupiter*).

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Surface composition of Europa?

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  1. Surface composition of Europa? What can we learn from in situ measurements in the exosphere and ionosphere? K. Altwegg, University of Bern

  2. Elemental, isotopic and molecular composition of Europa’s surface (by SIMS technology, primary ions provided by Jupiter*) • Surface volatiles (H2O, CO2, etc.) • N in the form of N2 or NH3 • Oxydation states of elements (CH4 vs. CO, • NO2 vs NH3) • Salts (hydrated) from the subsurface ocean • Fragments of organic (prebiotic) molecules • Isotopic ratios (D/H, 18O/16O, 15N/14N) • Oxygen isotopes (mixing of solar nebula) *for free! No mass, no power, no money!

  3. 1997

  4. Neutrals? • No interference by S/C charging • Less sensitivity • More interference from S/C outgassing Neutrals and ions complement each other! Ions? • Very sensitive measurements • Little interference from S/C outgassing • More interference from S/C charging, especially for low energy ions

  5. What can be measured in situ?

  6. ROSINA RosettaOrbiterSensorforIonand NeutralAnalysis DFMS RTOF DPU COPS

  7. Activity of C-G

  8. ROSINA Goals C-G minor constituents C-G Water Are these goals realistic?

  9. Dynamic range, DFMS Residual Gas Pressure: p_CO2 = 3*10-12 mbar Integration time 20 s, Ie = 20 mA GCU Gas Pressure p_CO2 = 1.8*10-6 mbar Integration time 20 s, Ie = 2 mA

  10. COPS

  11. Actual performance of ROSINA DFMS 10-11 10-12 10-13 10-14 Partial pressure (mbar) pCOPS = 6 e-11 mbar

  12. DFMS High resolution background mass spectrum, in space 6. 7. 2005, int. time 20 s/mass

  13. Performance of ROSINA DFMS with respect to Oxygen Isotopes Background spectrum 6. July 2005 in space, high resolution mode

  14. RTOF

  15. RTOF ion spectrum (ion energy < 15 eV)

  16. ROSINA-RTOF: Designed 1996 Mass 14.7 kg Power 28 W Resources? • Present day technology: • Current mass 14.7 kg • Cover - 2.0 kg • Second channel - 2.0 kg • Pump-off valve - 0.5 kg • HM pulser - 0.3 kg • C-F instead of • Titanium - 4.0 kg • Smaller E-box - 1.5 kg • Total 4.3 kg Designed for Ultra-high vacuum (no contamination from Earth) Two channels (ions and neutrals simultaneously) Has to tolerate high pressures and dust Very long mission duration Power: 10 W (one channel only) Advanced technology ???? Mass ~2.5 kg Power ~5 W

  17. Conclusions (1) • The main neutral species of Europa’s exosphere can be easily measured from an orbiter @ 200 km height • Many ion species of Europa’s ionosphere are easily accessible to a mass spectrometer on an orbiter • Ions and neutrals complement each other • From the composition of the exosphere and ionosphere the composition of the surface of Europa can be inferred, probably even the composition of the subsurface ocean (salts).

  18. Conclusions (2) • Many isotopic ratios in different molecules, especially D/H, 18O/16O, 13C/12C and 15N/14N can be determined. Heavy organic molecules can be inferred from their dissociation products (ion measurements). • However, the instrument needs a very good sensitivity (10-15 mbar (neutrals) / 10-3 cm-3 (ions)) and a good mass resolution (dm/m=1/3000 at 10 % level, N2 /CO!), not too many compromises! • Resources: ~4-5 kg, 10 W • A “clean” spacecraft is needed (from an outgassing and an electrostatic point of view)

  19. Eureca! EURopa Exosphere Composition Analysis

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