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Buscando a vida fora da Terra: Marte

AGA 0316 Aula 15. Buscando a vida fora da Terra: Marte. Why Mars is important for Astrobiology?. Relative proximity – first planet where we can realistically test in loco for biological potential and life

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Buscando a vida fora da Terra: Marte

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  1. AGA 0316 Aula 15 Buscando a vida fora da Terra:Marte

  2. Why Mars is important for Astrobiology? • Relative proximity – first planet where we can realistically test in loco for biological potential and life • Mars is in many ways similar to Earth. Rocky, terrestrial planet in the inner part of the Solar system with an atmosphere. Yet it is also very different. • Therefore if life is found there it would be a very strong argument in favor of life being an ubiquitous phenomenum in the galaxy

  3. History of Martian “Civilization” • In 1784 William Herschel (famous for the discovery of Uranus) claimed that Mars has an atmosphere and is therefore probably inhabited. • Giovanni Schiaparelli claimed to see a network of 79 linear channels (canali) in 1877 • Percival Lowell opened Lowell Observatory in Flagstaff, Arizona in 1894. (claimed to see 200 canals) • Lowell suggested that canals were built by an ancient martian civilization.

  4. Giovanni Schiaparelli William Herschel Percival Lowell

  5. In 1965 “Mariner 4” spacecraft send a few dozen good pictures of the Martian surface – no evidence for intelligent life. Mars is in fact a cold and dry planet! 6 7 9 1960’s 1970’s 1990’s 2000’s Spirit + Opportunity

  6. Mars Fact Sheet Parameter Value Units Diameter 6787 km Average Distance From the Sun 1.524 AU Average Temperature 210 K (-81 F) Mean Density 3.94 g/cm3 Rotational Period 24.6229 hours Mean Atmospheric Pressure 0.007 bars Surface Gravity 3.63 m/s2 Tilt of Axis 25.2 degrees Orbit period 687 days EARTH’S Atm CO2 0.04% N2 78,1% Ar 0.93% H2O 0 – 4 % Atmospheric Components Element Symbol Percentage Carbon Dioxide CO2 95.32 Nitrogen N2 2.7 Argon Ar 1.6 Water H2O 0.03

  7. Earth-Mars Similarities • Position in the Solar system – Martian orbit is 1.5 A.U.; Earth’s is 1 A.U. but Neptune’s is 30 A.U. • Similar bulk chemical composition – Si-rich crust and mantle and Fe-rich core • Size – Mars is only twice smaller than Earth by radius • Atmosphere has greenhouse gas (CO2) and some amount of nitrogen • Volcanoes • Similar rotation rate – 24.6 hours • Plenty of water (frozen; subsurface?)

  8. Earth-Mars Differences • Earth has a global-scale plate tectonics, Mars does not. • Earth has global oceans at its surface, Mars has not • Martian atmosphere (0.007 bar) is much thinner than Earth’s ( 1 bar) • Earth has an intrinsic global magnetic field, Mars has not

  9. Problems for life on the Martian surface • Cold (average temperature ~220K); not many known organisms on Earth can grow under these temperatures • Thin atmosphere – open liquid water is unstable • Very small amount of oxygen – no terrestrial-like animal life • Very little ozone – no UV protection • No magnetic field – poor protection from the cosmic rays

  10. Problem Water does not have a liquid phase under current low Martian pressures. Ice sublimates to water vapor directly. However, there are strong evidence that liquid water was present in the past on the Martian surface

  11. Evidence for liquid water on the Martian surface • Geomorphological evidence: 1) Look for features that are similar in appearance to terrestrial water-formed features 2) Degradation (weathering) of the ancient impact craters (erosion) • Mineralogical evidence

  12. MARTIAN SOIL

  13. FLOOD TRACES ON CRATER WALLS

  14. Valley network on the ancient terrain of the martian surface. Notice that valleys converge downstream. Individual valleys are about a kilometer across.

  15. Flood channel occurring on a relatively young surface. Note the well-defined margins of the channel indicating confined flow and the streamlined, tear-drop-shaped islands where erosional remnants have been left behind obstacles.

  16. Even the youngest features on Mars appear to show evidence for liquid water. Gullies have been identified on the walls of canyons, channels and impact craters. Most likely were formed by seepage of water from within the crust.

  17. Martian Meteorites • Meteorites which originated from Mars – impactors hit Martian surface and some small fraction of the ejected rock can arrive on Earth • Although > 31,000 meteorites were found, only 34 have been identified as Martian meteorites

  18. How do we know that some meteorites are from Mars? • Age. Almost all martian meteorites are relatively young volcanic rocks (180-1300 Myr) with composition similar to terrestrial basalts • Oxygen isotopes are distinct (16O, 17O, 18O) from terrestrial rocks and group all 34 meteorites together • The isotopic composition of gases trapped in the meteorites is almost identical to the Martian atmosphere (comparison with Viking measurements).

  19. The oxygen isotopic compositions of rocks from Earth, Mars, and the asteroid Vesta, the largest asteroid that melted, define three parallel lines on this plot of 17O / 16O vs. 18O / 16O. The lines are parallel because on each body the oxygen isotopes were separated according to their masses, when the rocks formed.

  20. Classification of Martian meteorites (SNC: shergottite, nakhlite, and chassigny) • 1 billion tones of Martian rocks crashed into Earth ! • Shergottite (Shergotty meteorite from India, 1865) - 25 • Nakhlites (Nakhla meteorite from Egypt, 1911) - 7 • Chassignites (Chassigny meteorite from France, 1815) - 2

  21. Evidence of water in SNCs • Carbonate minerals. Liquid water flows through fractures in rocks and dissolved CO2 can be precipitated. • Hydrated minerals with martian D/H Electron Microscope image of clay and carbonate (siderite) vein in Lafayette section. ol olivine.

  22. ALH84001 • Shergottite which containes structures that were considered to be the fossilized remains of bacteria-like lifeforms.

  23. Viking Mission • Two orbiters, two landers • Two landers landed on the opposite sides of Mars in 1976 • The Viking 1 Lander touched down at 22.7° N latitude and 48.2° W longitude • The Viking 2 Lander touched down at 48.3° N latitude and 226° W longitude

  24. Viking Results • Viking carried 4 instruments designed to detect any sign of biology: • The Labeled Release (LR), Gas Exchange (GEX), and Pyrolytic Release (PR) experiments, all designed to detect existent life on Mars. • The Gas Chromatograph/Mass Spectrometer (GC/MS) was capable of detecting organics at a level of a few parts per billion (ppb)

  25. Pyrolytic Release experiment (PR) • Martian soil was put in a chamber and exposed to CO2 and CO mixture • CO2 and CO were labeled with 14C • Idea: “If biota were in the soil it would incorporate some CO2 or CO and convert it to organic material” • Heat the soil  break organic material  look for release of 14C

  26. Gas exchange (GEX) • Martian soil was put into a chamber and mixed with plenty of different nutrients (amino acids, glucose, salts, vitamins ..) • Look for H2, N2, O2, CH4, CO2,and Ar, Kr (for calibration) released from the soil (bacteria?).

  27. Labeled release (LR) • Martian soil was put into a chamber and mixed with nutrients (glucose and sulfate) enriched in 14C and 35S • Look for gas release enriched in 14C and/or 35S (released by bacteria?)

  28. LR - TSM

  29. Biology Package • What the Viking biology experiments found: • The GC/MS detected no organics above the 10 ppb level

  30. What we expected • This was surprising as each year, 2.4 x 108 grams of reduced (organic) carbon is delivered to Mars each year by meteors, which should have been detectable by the Viking GC/MS. • Even without life, organics were expected. • With regolith mixing to a depth of 1 km, organics should be present at about 500 ppb.

  31. Viking Conclusions • It was concluded that the Martian surface is rich in UV-produced oxides and superoxides at the ppm level, which destroy any organics present. • This conclusion reconciles the apparently contradictory results of the other Viking life experiments. • However . . .(cf. OH-based life)

  32. The Atacama desert • Gonzáles et al. use the oxidizing soil and hyper-arid conditions in the Atacama Desert as an analog for the Martian surface. • They analyzed the Atacaman soil with a GC/MS to compare with Viking results.

  33. What they found • In the most arid sample, both formic acid and benzene were found when pyrolized at 750ºC. • However, Viking pyrolysis temperatures maxed out at 500ºC, so . . . • Using the Viking pyrolysis temperature, the formic acid detected was reduced by a factor of 4 and there was no benzene detected at all. formic acid benzene

  34. All three Viking’s experiments assumed that we would be able to culture potentially present martian organisms. • Even on Earth only 1 in 100 organisms can be cultures at best. • Viking results do not rule out the possibility of life in the martian soil. • Is there another way to discover martian life?

  35. Arguments in favor of “life on Mars” from ALH84001 • Presence of polycyclic aromatic hydrocarbons (PAHs). PAHs can form as decay products of microorganisms • Presence of magnetite crystals whose structure is very similar to crystals produced by some terrestrial bacteria • Ovoid structures in carbonate globules similar to terrestrial microbes

  36. PAHs Carbonate globules (50-250 m) Ovoid structures (20-100 nm) Magnetite crystalls (Fe3O4)

  37. History of ALH84001 • Age ~4.5 Gyr old (rock crystallized) • Carbonate globules are ~3.9 Gyr old • Rock remained on the surface of Mars until 16 Myr ago when it was ejected • Meteorite was captured by Earth 13,000 years ago and fell into Antarctica • Covered with snow and ice until 700 years ago • Recovered in 1984

  38. Summary of ALH84001 • Most of the morphological fossils are thought to be too small to represent living organisms • Most of the organics are terrestrial in origin and the martian organics could have been produced by nonbiological processes • The magnetite grains are thought to represent the strongest evidence for life • McKay et al. found fossil like structures in other Martian meteorites (Nakhla 1.3 Gyr and Shergotty 165 Myr)

  39. Can martian biota “hide” in the terrestrial biosphere? • Primitive life is very resilient. Some bacteria can grow under -15 C (and lower). Some bacteria has tolerance to extreme desiccation. Some bacteria are tolerant to UV and ionizing radiation. • Suppose a microorganism from Mars survived a trip to Earth • How would we distinguish between martian and terrestrial bugs?

  40. One possible clue is the ability to adapt to environments that could never have happened on Earth. (Pavlov et al., 2006) Radioresistance – tolerance to ionizing radiation (p.n,-rays) High radioresistance - totally unnecessary ability on Earth. Why are there bacteria like that on Earth? Why were them selected on Earth?

  41. Radioresistance 1. Extremely radioresistant bacteria : Deinococcus radiodurans , Rubrobacter radiotolerance, Rubrobacter xylanophilus, Chroococcidiopsis, Termococcus gammatolerance. Radioresistance is 100-1000 times higher than in other microorganisms 2. High doses of ionizing radiation create a lot of DNA damages and radioresistant bacteria have an unknown and unique mechanism for DNA repair (more 100 double strand breaks) 3. Lethal radiation dose >> dose accumulated during the lifetime of the radioresistant bacteria (by 10 orders of magnitude). Time of accumulation of the lethal doses is 106 – 108 years. Totally useless on Earth!

  42. Hypothesis • Radioresistant bacteria originated on Earth • Bacteria was transferred to Mars by meteorites • On Mars microorganisms acquired radioresistance ability • Radioresistant bacteria were transferred back to Earth by Martian meteorites

  43. Gamma radiation survival curves of theЕscherichia coli (rhombus) andDeinococcus radiodurans (squares)(Battista et al, 1999). S – surviving fraction of the bacterial population 1 Gy = 1 J/kg 5 Gy is lethal for humans within two weeksBackground radiation on Earth: 0.0005 Gy/year

  44. Experiment with Deinococcus Radiodurans at LNLS (Lima et al. 2009)

  45. Why Mars? Great oscillations in Martian obliquity (period 1.2x105 years)  oscillations of annual insulation of the polar regions  dramatic regular oscillations of global climate and atmospheric mass  long periods of the “frozen state” for subsurface layers  long periods of the bacterial dormancy Low atmospheric mass , no magnetic field  Irradiation of cosmic rays in subsurface layers of Mars 100-fold of the terrestrial irradiation  Periods of sublethal doses accumulation 104 years.  Total time of “training process” (100 cycles) 106 years

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