1. Julian Chela-Flores The Abdus Salam ICTP, Trieste, Italia and Instituto de Estudios Avanzados, Caracas, Republica Bolivariana de Venezuela Can a future mission detect a habitable ecosystem on Europa, or Ganymede?

2. Io Europa Ganymede EJSM (JGO) EJSM (JEO) Callisto The Europa Jupiter System Mission (EJSM)

3. Top questions: The search for habitable ecosystems (a question in geochemistry, 1970s, Vikings). The search for the origin of life itself (a question in chemical evolution, 1920).

4. Top questions: The search for habitable ecosystems (a question in geochemistry, 1970s, Vikings). The search for the origin of life itself (a question in chemical evolution, 1920).

5. Can we identify reliable biomarkers on Europa with EJSM?

6. Oceans in contact with silicate cores in the Solar System  Working hypothesis: The ocean-core interface can provide a variety of chemical elements for sustaining life. Europa Ice-core interface Earth Ocean-core interface

7. The geochemistry of Europa: ______________________________ There is a unique opportunity to focus on another Earth-like world with EJSM by probing 1 and confirming 2: There is a unique opportunity to focus on another Earth-like world with EJSM by probing 1 and confirming 2: _______ _ ________________________ 2. Liquid ocean in contact with its silicate core 1. Stained icy surface

8. Plan of the talk Analysis: Analysis: 1. The stained icy surface of Europa.1. The stained icy surface of Europa. 2. The liquid Europan ocean in contact with its silicate core.2. The liquid Europan ocean in contact with its silicate core.Conclusions: Instrumentation for identifying reliable biomarkers.Instrumentation for identifying reliable biomarkers. An EJSM test for a habitable ecosystem on Europa.An EJSM test for a habitable ecosystem on Europa.

9. 1. The stained icy surface of Europa International Journal of Astrobiology (April, 2010) (Cambridge University Press).

10. There are alternative views on the effect of space weather on the surficial patches. But S is common to both interpretations of the radiation-induced S-cycles produced on the surface. Galileo Mission, 1995-2003

11. To get insights into the significance of the sulfur patches on the icy surface of Europa, we should look at the sulfur patches on icy terrestrial surfaces.

12. What do we know about sulfur icy patches on Earth? Antarctica

13. C: Canada Glacier F: Lake Fryxell H: Lake Hoare Taylor Valley

14. Underneath the surface of these lakes Algal mat pieces

15. The icy surface of Lake Hoare (Taylor Valley) Algal mat pieces on the surface of Lake Hoare (Parker et al, Phycologia, 1982) Algal mat pieces

16. The larger Taylor Valley lakes Biogenic sulfur on the icy surfaces of Taylor valley lakes (5.4 sq.km)(1.8 sq. km)( ) [Annual escape of biogenic sulfur (kg)]

17. 2. Implications of Europa’s ocean in contact with its silicate core. External Jovian magnetosphere source, is excluded due to the patchy nature of the stains. External Jovian magnetosphere source, is excluded due to the patchy nature of the stains. Internal source: Internal source: Cryovolcanism, or biogenic. Cryovolcanism, or biogenic. Geochemistry allows to select between these two possibilities. Geochemistry allows to select between these two possibilities.

18. The biogenic hypothesis

19. Sulfate-reducing bacteria 4H 2 + H 2 SO 4 –» H 2 S + 4H 2 O + 39 kilocalories 4H 2 + H 2 SO 4 –» H 2 S + 4H 2 O + 39 kilocalories  The H 2 S then combines with Fe in sediments to form grains of the biogenic mineral pyrite.  Unite H with S atoms from dissolved sulfate ( SO 4 -2 ) of seawater to form hydrogen sulfide H 2 S : of seawater to form hydrogen sulfide H 2 S : Iron sulfide, FeS 2

20. Processing sulfur in the Solar System  Dissolved sulfate: on evaporation sulfate minerals are depleted of 32 S by 20 per mil.  The H 2 S given off by S-hungry bacteria is enriched in 32 S by 20 per mil. Large depletion: Microbial single-step large sulfur fractionation

21. Biogenic S on icy surfaces Terrestrial Meteoritic Lunar -70 per mill (extreme fractionation)  The Integrated Ocean- Drilling Program (IODP) while exploring terrestrial structure has identified extreme fractionation on the Australian seafloor. Modern sulfate coexisting with ocean water (21 per mill) The delta 34 S-parameter  Large, and even extreme depletion of sulfur takes place on terrestrial ecosystems. ( per mill )

22. Instrumentation required for identifying reliable biomarkers Credit: British Consortium

23. Penetrators for probing Europa’s icy surface Penetrators for probing Europa’s icy surface Credit: British Consortium

24. Gowen et al., 2009 Penetrators should be inserted in the EJSM orbital probes: JEO and JGO.

25. To answer what is the meaning of the Europan icy patches we should go beyond measurements from JEO alone for detection of biomarkers.

26. lower values of 34S. lower values of 34S. lower values of 34S. lower values of 34S. Both JEO and JGO can test biogenicity with two sets of penetrators JGO+penetrator JEO+penetrator Ganymede, ESA Europa, NASA

27. An EJSM test for a habitable ecosystem on Europa  We expect diverging results from mass spectrometry: — large minus  34 S for Europa, and — large minus  34 S for Europa, and — small minus  34 S for Ganymede. — small minus  34 S for Ganymede.  Such data would provide a test of a habitable ecosystem on Europa.