Julian Chela-Flores The Abdus Salam ICTP, Trieste, Italia and

1. Evolution of the universe: • From Astrophysics to Astrobiology Exploring the Solar System - Missions and Techniques EGU 2008, Austria Center Vienna, Lecture Room 11; 15 April 2008: 9.15 Distinguishing between signatures of past life and nonlife Julian Chela-Flores The Abdus Salam ICTP, Trieste, Italia and Instituto de Estudios Avanzados, Caracas, Republica Bolivariana de Venezuela The Origins: how, when and where it all started, Accademia Nazionale dei Lincei. Centro Linceo Interdisciplinare “Beniamino Segre”, Roma, 22 May 2006

2. Authors Julian Chela-Flores The Abdus Salam ICTP, Trieste, Italia and Instituto de Estudios Avanzados, Caracas, Republica Bolivariana de Venezuela Narendra Kumar Indian Institute of Science, Bangalore, India Joseph Seckbach The Hebrew University of Jerusalem Israel Vinod Tewari Wadia Institute of Himalayan Geology Dehradun, India.

3. Future missions to Europa • There is a possibility for returning to Europa with both the LAPLACE mission, and the Europa Geophysical Explorer. • The outline of LAPLACE has been summarised by Blanc, M. and the LAPLACE consortium (2008). Europa Geophysical Explorer

4. Habitability • “Is Europa habitable?” plays a prominent role in ESA’s Cosmic Vision Plan for 2015-2025 that has been adopted for the LAPLACE mission. The other two Goals are related with habitability: • What have been the conditions for the formation of the Jupiter system? How do they contribute to the possible emergence of life? • How does the Jupiter system work? How does the system contribute to the conditions for habitability? • For NASA's Science Mission Directoratehabitability is also the focus of its Solar System Exploration Roadmap.

5. Plan of the talk • The patchy surface of Europa: A major challenge in the exploration of Europa. • Chemical elements on the surface of Antarctica and Europa. • Biogeochemistry. • A ‘fluctuation test’ for the exploration of Europa. • Instrumentation. • Discussion.

6. Part I The patchy surface of Europa: A major challenge in the exploration of Europa International Journal of Astrobiology (2006), 5, pp. 17-22 (Cambridge University Press).

7. Ice-covered oceans over a silicate core: The cases of Europa and Titan

8. Galileo revealed evidence for an internal ocean, but we argue that for determining the habitability of Europa, waiting to enter the ocean by 2028 may be unnecessary. Horvath et al, 1997 A hydrobot Endurance, 2008

9. Possible sources of the stains • External source: Ions may be implanted from the Jovian plasma. • Internal source: Sulfur may be due to cryovolcanism. • Could the source be biogenic? We discuss the use of mass spectrometry in the context of the available instrumentation.

10. Part II Chemical elements on the surface of Antarctica and Europa

11. Antarctica’s subglacial lakes

12. Antarctica’s Dry Valleys: • Beacon • Taylor • Victoria • Wright

13. Lake Bonney (7) Lake Hoare (9) The Taylor (Dry) Valley

14. A cross-section of the icy surface of Lake Hoare Algal mat pieces on the surface of Lake Hoare (Parker et al, Phycologia, 1982)

15. Annual escape of sulfur (kg) by the loss of algal mats

16. The Europa icy surface (Spectrometer data from near IR) and ‘patchy’ Distribution of non-ice component albedo per pixel McCord et al, Science 280 (1998), 1242 4 km/pixel High resolution albedo image

17. Where should we land?

18. Part III Biogeochemistry

19. The delta 34S-parameter • The Canyon Diablo Meteorite (CDM) is a troilite (FeS), that was found in Arizona: • The meteorite coincides with the standard (st) terrestrial ratio of the isotopes 32S and 34S. For a given sample (sa), we define with respect to this meteorite:

20. Sulfate-reducing bacteria

21. Sulfate-reducing bacteria • Unite H with S atoms from dissolved sulfate ( SO4-2 ) of seawater to form hydrogen sulfide H2S : 4H2 + H2SO4 –» H2S + 4H2O + 39 kilocalories • The H2S then combines with Fe in sediments to form grains of the biogenic mineral pyrite. Iron sulfide, FeS2

22. The sulfur isotopes are divided between biogenic minerals and sulfate minerals • Dissolved sulfate on evaporation forms sulfate minerals depleted of 32S by 20 per mil. • The H2S given off by the bacteria is enriched in 32S by 20 per mil.

23. Sulfur ions on Earth, meteorites and the Moon The delta34S-parameter Terrestrial Sulfate coexisting with seawater From measurements in basins off California: insoluble sulfide, mostly pyrite. -40 Meteoritic Lunar

24. Part IV A ‘fluctuation test’ for the exploration of Europa

25. The fluctuation test (Luria and Delbruck) • Luria first assumed that mutations in a growing bacterial culture could be acquired as a result of its exposure to virus (phage). • If this was the case, the number of resistant individuals would vary very little from one experiment to the next. • The observed number would then have very small fluctuations (slight deviations from the mean).

26. Can bacterial fluctuations be large? • Alternatively, Luria also assumed that a mutation can occur before the bacterium was confronted with phage. • The number of resistant bacteria would depend on the time elapsed since the mutation. The number of resistant individuals shows exponentially large fluctuations. • The observed bacterial exponential growth suggests to detect such deviations from Gaussianity with higher order statistics.

27. Part V Instrumentation

28. Difficulties with the the dust analyzers • 32S is isobaric (same m/z) with 16O2. There would not have sufficient resolution with the current design to identify the contributions from S and its interference with the O2 at m/z 32 and 34. • The instrument required needs to count about 1x106 sulfur ions to get a precision of +/- 5 per mil on the delta34S-parameter. So the likely ion counts is a key issue.

29. The cloud generated around Europa • We expect it to mirror the large S-isotope deviations on the surface. • Consequently, dust detectors in orbit should record similar non-Gaussian distributions as conjectured for the surface itself, with non-vanishing cumulants of order greater than 2. • On the other hand, the contributions from the O2 atmosphere should be described instead by a Gaussian distribution with vanishing cumulants of order greater than 2.

30. A possible instrument is a penetrator • A UK Consortium has already argued in favour of landing with penetrators on the icy surface of Europa. • Penetrators are considered in the recent paper of Blanc, M. and the LAPLACE consortium summarising the mission. • In this case, if the Europan surface is to be probed with penetrators, MS would be a valuable alternative for understanding the icy patches.

31. The mass constraints for MS on penetrators are severe • To illustrate that miniaturization is not the main challenge, we point out suitable instrumentation: • The current MS on Cassini (Ion and neutral MS), and • The work on miniaturised MS by Peter Wurz and co-workers at the University of Bern. 120 x 60 mm; 500 g

32. Discussion • The work of miniaturization of the instrumentation does not seem to be the greatest challenge in interpreting S-isotopes either in orbit or on the icy surface of Europa. • The use of MS is suggested for a dust analyzer and, if landers are possible, MS is also suggested for penetrators.

33. pdf files can be downloaded from:http://www.ictp.it/~chelaf/ss16a.html