Life in the Universe

1. Life in the Universe

2. Stuff. Lots of stuff. • 100 billion+ star systems in the Milky Way • New exoplanets being discovered every day • 100 billion+ galaxies in observable universe • Carbon can arrange in many, many ways… • Given that and the amount of matter, nature can experiment practically an infinite number of times.

3. Two Possibilities • We hope that we can: • Find microbial life in our Solar System • Find EM signals from extra-solar civilizations

4. Life on Earth • Earth was born 4.5 billion years ago • Heavy bombardment from 4.2 to 3.9 billion years ago • Life was thriving prior to 3.85 billion years ago

5. Life on Earth • So just as soon as the oceans quit getting vaporized by asteroids, life sprang into action – in an instant!

6. Timeline

7. Stromatolites • “Mats” of bacteria build layered rocks • We see them today, we see similar ones from long ago • Dated to 3.5 billion years

8. Life In Extremes • Oldest microbes (from DNA standpoint): • Live near “black smokers” in the ocean • Live in hot springs in Yellowstone

9. First Living Organisms • Why did early life hang around extremes? • Earth may not have had an ozone layer yet; hide out from UV

10. Life In Extremes • “Ice worms” live in glacial ice

11. Titan (a moon of Saturn) • Lakes, rivers and thick atmosphere of basic organic molecules have been observed

12. Titan (a moon of Saturn) • Chemists have recreated the pressure, temperature, and chemistry of Titan’s atmosphere • They found: • Nucleotide bases • Amino acids

13. What do we need? • Source of nutrients to build living cells • Organic molecules all over the Solar System • Energy for activity • Sunlight, internal heat from a planet • Liquid water • That’s the tough one.

14. Life in the Solar System • Liquid water requirement leaves us with: • Mars • Jovian moons, particularly Europa

15. Life on Mars • Evidence: Mars once thriving waterworld • Martian meteorite may show evidence for life

16. Life on Jovian Moons • Tidal heating • Evidence for water flow • Thick water-ice surfaces • But not much energy from sunlight

17. Jovian Under-Water Worlds (?) Europa Ganymede Callisto Enceladus Titan

18. Life Around Other Stars • Life may only take ten thousand years to form • Intelligent life may take a few billion years • Excludes blue stars; they only last 100 million years • Sun-like stars and red dwarfs good candidates

19. Life Around Other Stars • Habitable zone: Smaller and closer for smaller stars

20. Galactic Habitability • Outer galaxy: • Too few heavy elements • Inner galaxy: • More crowded, supernovas would nuke everything

21. Signs of Life • When an exoplanet transits a star, starlight passes through the planet’s atmosphere • This is a cutting-edge technique, but does reveal chemical composition of the planet • Look for carbon dioxide, ozone, methane, and water vapor • Oxygen abundance on Earth result of biology

22. Signs of Life • It is entirely possible that extraterrestrial civilizations could be using this technique to monitor our progress. Perhaps at some point: • We become cool enough to make friends • We become advanced enough to pose a threat

23. Jovian Planets: Comet Launchers • Jovian planets launched trillions of objects into the Oort Cloud • These objects now pose no danger to Earth • Might “comet launchers” be a prerequisite for intelligent civilizations?

24. The Drake Equation Number of “Contactable” Civilizations = NHP x flife x fciv x fnow NHP = Number of habitable planets in the galaxy flife = Fraction of planets that are habitable fciv = Fraction of planets that can communicate fnow = Fraction of planets that have a civilization now

25. Another Approach • EM waves travel forever – but get weaker • Look for signs of communication • SETI (Search for ExtraTerrestrial Intelligence) does that all day

26. And Just The Opposite • We have deliberately sent high-power signals into space to “make contact” • Used Arecibo in 1974 to send to M13 (21k LY away)

27. Interstellar Travel • Einstein’s Theory of Relativity limits all speeds to the speed of light • Out fastest spacecraft are travelling 1/10,000 the speed of light • 100,000 years to Alpha Centauri (but not pointing there) • Time dilation and length contraction: • At 99.9% the speed of light, 2 years pass for the astronauts while 50 years pass on Earth

28. Interstellar Travel Ideas • Scoop up hydrogen and fuse it • Detonate atomic bombs to propel the ship

29. Interstellar Travel • So we either build generational ships or we figure out how to warp space and time • We don’t know how to warp space and time, but current laws of physics don’t seem to prevent it

30. Aliens • Even our “slow” spaceships could populate stars within a few hundred LY • Would take about 10,000 years – an instant in the overall scheme of the Universe • In a few million years, we could colonize the galaxy • A few million years? This should have been done a long time ago.

31. Aliens • 1 in 1 million chance a star will have life • 100 billion stars in Milky Way: 100,000 civilizations • Suppose intelligent civilizations arise after 5 billion years • Galaxy is 12 billion years old • 100,000 civilizations should have arisen 7 billion years ago – billions of years ahead of us

32. Aliens So… where are the aliens?

33. Aliens • Galactic civilization should already exist! Three possibilities • We are alone • … and therefore precious. The only part of the Universe that is self-aware. • Civilizations are common but they haven’t bothered colonizing the galaxy • We explore every chance we get. Do they always end up destroying themselves? • The galactic civilization hasn’t gotten around to us • Are we not yet invited?