The Search for Life Beyond Earth

1. Phys 1810: Lecture 34 Life on Other Worlds continued. No more Star Fleet Academy Monday is last office hour. Example of Extremophiles: Tube worms near Black Smoker Those who have been floating between morning and afternoon, please go to P&A office Allen 301 and do an SEEQ Note: typo λ should be capital Λ in ΛCDM

2. 2. Chemical Evolution off planet Panspermia: possible that complex organic molecules came from outside Earth, on meteorites or comets. Lab experiment: Droplets rich in amino acids, formed when a freezing mix of primordial matter was subjected to harsh ultraviolet radiation.

3. 2. Chemical Evolution Off Planet • Complex Molecules: • Organic molecules usually found in star-forming regions consist of a single “backbone” of carbon atoms arranged in a straight chain. • ALMA found, in ISM, isopropyl cyanide which has branching structure. • Branched carbon structure is common feature in amino acids • May find way to planets.

4. 2. Chemical Evolution Off Planet This meteorite contains 12 different amino acids found in Earthly life, although some of them are slightly different in form.

5. 2. Chemical Evolution Off Planet Would amino acids survive impact? • two-stage light gas gun, fired frozen pellets of algae into H2O • v = 6.93 km/s, expected velocity of meteorite hitting earth-like planet • a small proportion survived.

6. 2. Chemical Evolution Off Planet Would amino acids survive? Simulations  at ~1% level. Comparable with Urey-Miller experiment level.

7. 2. Chemical Evolution Off Planet • Meteorite/Comet – produce instead of deliver • oblique collision: • CO2 icy comet impacts a planetary atmosphere with glancing blow  thermodynamic conditions conducive to organic synthesis e.g. PAHs. • also for rocky meteorite with icy surface. • impact creates shock wave that generates molecules that make up amino acids. • impact of the shock wave also generates heat •  transforms these molecules into amino acids. • - fired projectiles through a large high speed gun at speeds of 7.15 km/s into targets of ice mixtures (comet-like)  amino acids Why not both 1 & 2? 

8. Role of the Moon • Early Earth environment had fast lunar tidal oscillations since moon closer. • highly saline low-tide environment needed for protonucleic acid fragments to assemble into complementary molecular strands.
 • Rocks can provide scaffold-like structure to help chains grow. •  DNA

9. Cosmic Evolution • Simple one-celled creatures, such as algae, appeared on Earth ~ 3.5 billion years ago. • More complex one-celled creatures, such as amoeba, appeared ~ 2 billion years ago. • Multicellular organisms began to appear ~1 billion years ago. • The entirety of human civilization has been created in the last 10,000 years.

10. Life in the Solar System Even on Earth, organisms called extremophiles survive in environments long thought impossible—here, hydrothermal vents emitting boiling water rich in sulfur.

11. Extremophiles: • under 4km ice • cut off from the outside world for millions of years • unique microbial communities • 3,500+ species in conditions similar to Jupiter’s Europa

12. Extremophiles: Tube worms near Black Smoker Dr Verena Tunnicliffe, University of Victoria (UVic) • Example of energy source where the is no sunlight. • Deep in the ocean, hydrothermal vent called a Black Smoker. • Rich ecosystem near the vent. • Relevant to moons like Europa which has internal heat caused by the tidal force of Jupiter and seems to have a liquid ocean.

13. Extremophiles • Methanogenic microbes: • H consuming. • Produce methane. •  Europa, Titan? Endoliths: Rock eating microbes  Mars?

14. Extremophiles: Pointing to microbes living in rock in Yellowstone Park University of Colorado, Jeffrey Walker • Other examples include • microbes in salty ice (relevant to Mars, Europa and other Jovian moons). • microbes in layers of rock (relevant to Mars)

15. Life in the Solar System Has Mars had liquid water on its surface in past? Martian landers have analyzed soil, looking for signs of life—either fossilized or recent. Spirit Rover/NASA

16. Life on Mars • Phoenix mission discovered a chemical -- Perchlorates – that • is food for some microbes on Earth. • b) is toxic to some microbes on Earth. • c) collects water from an atmosphere. • d) is capable of creating on Mars wet habitats that are about the size of sand grains. • Toxic for humans • evidence of carbon compounds In past, warm humid conditions BENEATH surface suitable. Curiosity: Found “habitable region” – just add liquid H2O Results: inconclusive.

17. Life in the Solar System • Life as we know it: carbon-based, originated in liquid water • Is such life likely to be found elsewhere in our Solar System? • Best bet: Mars • Long shots: Europa, Titan, Ganymede, Enceladus • Other places are all but ruled out?

18. The Virus • Are viruses alive? • contain some protein & genetic material • cannot be considered alive until they become part of a host cell. • They transfer their genetic material into cell, take over chemical activity, & reproduce. • Viruses are in a “gray area” between living & nonliving, -- serve as a reminder of how complex the definition of life can be.

19. Life in the Solar System What about alternative biochemistries? Some have suggested that life could be based on silicon rather than carbon, as it has similar chemistry. Or the liquid could be ammonia or methane rather than water. However, silicon is much less likely to form complex molecules, & liquid ammonia or methane would be very cold, making chemical reactions proceed very slowly.

20. Alternatives – Life as we don’t know it: • Astrobiologists ARE looking for alternatives not found on Earth. • e.g. silicon instead of carbon and sulfuric acid instead of water. • e.g. The University of Vienna’s Alternative Solvents as a Basis for Life Supporting Zones in (Exo-)Planetary Systems.

21. Life on Other Worlds • Difficult to define life (e.g. viruses) • Expect these requirements: • solvent for metabolism • e.g. water or sulfuric acid • raw materials • e.g. carbon or silicon • clement conditions • e.g. distance from star for temperature or magnetic field to protect from cosmic rays or depth within soil to protect from UV. • energy source • e.g. star or internal heat from tidal forces (e.g. Europa).

22. Can we constrain this or is it hopeless? Critical Thinking. • Example: Jack is looking at Anne but Anne is looking at George. Jack is married but George is not. Is a married person looking at an unmarried person? • Yes • No • Not enough information to decide YES!

23. 28.3 Intelligent Life in the Galaxy The Drake equation, illustrated here, is a series of estimates of factors that must be present for a long-lasting technological civilization to arise. Estimates the number of civilizations we could attempt to communicate with in the Milky Way Galaxy at any representative time (such as the present). Make your own estimate!

24. 28.3 Intelligent Life in the Galaxy Look at 1st term in more detail than textbook. Divide by time at the end.

25. Life as we know it – searching for Mr. Spock. More accurately determined. Difficult to estimate. • N = the number of civilizations now = # of stars in the Milky Way * fraction of appropriate stars * fraction of those stars with planetary systems * # of planets suitable for life in each exoplanet system *fraction of suitable planets upon which intelligent life appears * fraction of planets that produce a civilization with interstellar communication * lifetime of that civilization / time that appropriate stars have existed.

26. Life as we know it – searching for Mr. Spock. Term 1  Term 2  Term 3  Term 4  Term 5  • N = the number of civilizations now = # of stars in the Milky Way * fraction of appropriate stars * fraction of those stars with planetary systems * # of planets suitable for life in each exoplanet system *fraction of suitable planets upon which intelligent life appears * fraction of planets that produce a civilization with interstellar communication * lifetime of that civilization / time that appropriate stars have existed. Term 6  Term 7  Term 8 

27. Drake’s Equation: Term 1 • The number of stars in the Milky Way: • F_orbit = F_gravity • M = (r * v**2) /G • M = a few * 10 **11 solar masses. • Adopt 300 billion stars as the estimate • e.g. there are only a few % high mass stars on the main sequence.

28. Drake’s Equation: Term 2 Galactic Habitable Zones: PAH’s exist in these regions. • The number appropriate stars: • Need high enough metallicity to have carbon (or silicon) on their planets.

29. Which of the following stars are metal-poor? a) Very young stars. b) Population II stars. c) Population I stars. d) Stars forming in spiral arms of galaxies.

30. Drake’s Equation: Term 2 • The number appropriate stars: • Need high enough metallicity to have carbon (or silicon) on their planets. • Population I stars. • up to 1/5 are Pop II • leaves us with roughly 250 * 10**9 stars.

31. Drake’s Equation: Term 2 • The number appropriate stars: b) Need long enough lifetime for life to form and evolve. On Earth it formed at roughly 3 billion years. So a star can’t be too massive. • Spectral Types F through K. • 1/17 * 250 * 10**9 stars = 15 * 10**9 stars.  ~ 15 billion stars

32. Drake’s Equation: Term 3 • The number appropriate stars with planetary systems: a) Should have Jupiter-size planets far from planet hosting life. These will attract comets away from planet with life. From studies of exoplanet systems: • 1/5 * 15 * 10**9 stars = 3 * 10**9 stars

33. Drake’s Equation: Term 3 Start to incorporate your own values! Optimists use “1” i.e. all systems have rocky planets. Text notes that planets in binary systems unlikely to have stable orbit. Uses 1/10. • The number appropriate stars with planetary systems: b) How many have rocky planets? 50-50 chance: • ½ * 3 * 10**9 stars = roughly 1.5 *10**9 stars with at least 1 rocky planet.

34. Drake’s Equation: Term 4 For example, our sun (G star) 0.85 AU < HZ < 2 AU • The number of planets suitable for life in each exoplanet system: How many rocky planets reside in the Habitable Zone (HZ)? This zone is around each star and has a temperature such that water condenses on the planet’s surface but does not permanently freeze. That is, it is a spherical shell bound on the interior by regions with T > 100C and outside by T<0C. 0.85 AU < HZ < 2 AU

35. Drake’s Equation: Term 4 • The number of planets suitable for life in each exoplanet system: How many rocky planets reside in the Habitable Zone (HZ)? Using our solar system as an example, almost 3 rocky planets are in the HZ. • 1 planet is too hot • 1 planet has too little mass to retain its solvent as a liquid. • adopt the value of 1 appropriate planet in the HZ • 1 * 1.5 * 10**9 stars When you make your own calculation, adjust this up to “3 times” if you like.

36. Drake’s Equation: Term 5 • What fraction of suitable planets produce life? • e.g. given the ingredients (C, N, H and H20) and assuming life spontaneously arises. • 50-50 chance • ½ * 1.5 * 10**9 stars = roughly 1 * 10**9 stars with a planet with life on it. Textbook uses 1 – optimistically = 1.5 billion stars. Dimitar Sasselov TED talk 2010: 100 million habitable planets. Sara Seager TEDX talk 2013: ~2 dozen Earth-like planets discovered.

37. Drake’s Equation: Term 6 • What fraction of planets with life produce intelligent civilizations that develop a technology that releases detectable signs of their existence into space? • e.g. of Issues - Mass extinctions: • one needed to wipe out the dinosaurs. • alternatively it could wipe out life either altogether or to the microbial stage. • perhaps less than 50% of the exoplanet systems are lucky to have this happen and survive???  1/3 * 10**9 stars The least constrained term is term 7, life time of the technological civilization. Let’s leave this for the moment.

38. What is true about this image? • It is the famous Ring Nebula. • Our sun will look like this as it dies. • Carbon is an element in these objects. • It is a Planetary Nebula. • All of the above.

39. Drake’s Equation: Term 8 • How long have appropriate stars existed? • i.e. How long has carbon existed? • study elements in Planetary Nebulae and those that are younger than ~6 * 10**9 years old have enough carbon.  the civilizations we seek have occurred within the last 10 billion years (c.f. Universe’s age 13.5 billion years)

40. Life as we know it – searching for Mr. Spock. What is your estimate for N? N = your_fraction * lifetime of that civilization • N = the number of civilizations now N = 1/3 * 10**9 stars * lifetime of that civilization / 10 * 10**9 yr N = lifetime of that civilization / 30 Other estimates in next lecture.