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Habiatal Zone (outside our solar system)


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Habiatal Zone (outside our solar system)

  1. 1. Habitability Outside the Solar System
  2. 2. Overview <ul><li>Distant Suns </li></ul><ul><ul><li>Life cycle of stars and their habitability zones </li></ul></ul><ul><li>Extrasolar Planets: Discoveries and Implications </li></ul><ul><ul><li>detection methodologies </li></ul></ul><ul><li>The Possibilities that Earth is Rare </li></ul><ul><li>The Process of Science in Action: Classifying Stars </li></ul><ul><li>The Drake Equation </li></ul>
  3. 3. Are Habitable Planets Common? <ul><li>Really two questions </li></ul><ul><ul><li>Are planets common? </li></ul></ul><ul><ul><li>How many exoplanets are habitable? </li></ul></ul><ul><li>Review formation of stars and planets </li></ul><ul><ul><li>evidence from HST </li></ul></ul>
  4. 4. Habitability Zone Around Other Stars in Our Galaxy <ul><li>Use the range from our solar system as a basis for analysis </li></ul><ul><ul><li>In our solar system, 4 rocky planets that orbit the Sun from 0.4 to 1.4 AU and spaced 0.4 AU apart </li></ul></ul><ul><li>If typical, likelihood of other solar systems having continuous habitability zone is just width of the zone divided by the typical spacing </li></ul><ul><ul><li>0.2/0.4 = 0.5 </li></ul></ul><ul><ul><li>Probability of 50% </li></ul></ul><ul><ul><li>Discuss this probability </li></ul></ul>
  5. 5. Habitability Zone in Our Galaxy <ul><li>Other factors also relevant </li></ul><ul><ul><li>Several stars in our galaxy with planets the size of Jupiter within terrestrial zone from their sun </li></ul></ul><ul><ul><li>Mass of star </li></ul></ul><ul><ul><ul><li>Larger mass, greater luminosity, shorter life </li></ul></ul></ul><ul><ul><ul><li>Most abundant stars in galaxy are least luminous and longest-lived (red dwarfs) </li></ul></ul></ul>
  6. 6. Habitability Zones Elsewhere in the Galaxy Using Star Size
  7. 7. Different Stars – Different Habitable Zones Athena Andreadis, in Astronomy , Jan. 1999, illus. by Terri Field
  8. 8. Another View of Habitability
  9. 9. Question <ul><li>Compared to a star of spectral type K, a star of spectral type A is generally </li></ul><ul><ul><li>A hotter, more luminous, and more massive. </li></ul></ul><ul><ul><li>B hotter, more luminous, and less massive. </li></ul></ul><ul><ul><li>C cooler, dimmer and less massive. </li></ul></ul>
  10. 10. Question <ul><li>How does the habitable zone around a star of spectral type M compare to that around a star of spectral type G? </li></ul><ul><ul><li>A It’s larger and farther from its star. </li></ul></ul><ul><ul><li>B It’s hotter and brighter. </li></ul></ul><ul><ul><li>C It’s smaller and closer to its star. </li></ul></ul>
  11. 11. How to Find an Extrasolar Planet <ul><li>Think about how a planet effects the star around which it orbits </li></ul><ul><ul><li>light seen from star </li></ul></ul><ul><ul><li>gravitational effects </li></ul></ul><ul><ul><ul><li>translate into visual effects </li></ul></ul></ul><ul><ul><li>spectroscopic effects </li></ul></ul><ul><ul><ul><li>translate into observed spectroscopic observations </li></ul></ul></ul><ul><ul><ul><li>remember Doppler Effect </li></ul></ul></ul>
  12. 12. Four Main Ways to Find an Extrasolar Planet <ul><li>Photometrically </li></ul><ul><ul><li>light from star blocked by planet decreasing light seen from star in concert with orbit </li></ul></ul><ul><li>Astrometrically </li></ul><ul><ul><li>change in position caused by “dance with planet” </li></ul></ul><ul><li>Spectroscopically </li></ul><ul><ul><li>Doppler Effect on spectral lines due to “dance with planet” </li></ul></ul><ul><li>Gravitational Microlensing </li></ul><ul><ul><li>large gravitational force effecting light path </li></ul></ul>
  13. 14. Change in position of Sun due to Jupiter as seen from 10 parsecs distant
  14. 15. Remember Doppler
  15. 16. Applying Doppler
  16. 17. Applying Einstein
  17. 18. Extrasolar Planet Detection Capability
  18. 21. Considerations for Habitability <ul><li>Distance from sun </li></ul><ul><li>Luminosity of sun </li></ul><ul><li>Planet size </li></ul><ul><li>Atmospheric loss processes </li></ul><ul><li>Greenhouse effect and gases in the atmosphere </li></ul><ul><li>Source of energy (internal/external) </li></ul><ul><li>Presence of water </li></ul><ul><li>Presence of carbon biomolecules </li></ul><ul><li>Biota </li></ul>
  19. 22. Phases of Water and CO 2
  20. 23. Planetary Spectra
  21. 24. Planet Size Questions <ul><li>Tectonics: why important </li></ul><ul><li>Magnetosphere and solar winds </li></ul><ul><li>Gravity and tectonics </li></ul>
  22. 25. Atmospheric Loss Processes to Consider <ul><li>Solar winds of charged particles </li></ul><ul><ul><li>Sweeps away atmosphere in episodic wind events </li></ul></ul><ul><li>Planet’s magnetic field (magnetosphere) </li></ul><ul><ul><li>Deflect solar winds </li></ul></ul><ul><ul><li>Earth and Mercury have magnetospheres </li></ul></ul><ul><ul><li>Mars and Venus do not have magnetospheres </li></ul></ul><ul><li>Atmospheric loss processes </li></ul><ul><ul><li>Escape velocity of gases </li></ul></ul>
  23. 26. Question <ul><li>About how many extrasolar planets have been detected to date? </li></ul><ul><ul><li>A between 10 and 100 </li></ul></ul><ul><ul><li>B between 100 and 1000 </li></ul></ul><ul><ul><li>C more than 1000 </li></ul></ul>
  24. 27. Question <ul><li>How have we detected most extrasolar planets discovered to date? </li></ul><ul><ul><li>A Transits </li></ul></ul><ul><ul><li>B Hubble Space Telescope images </li></ul></ul><ul><ul><li>C the Doppler related technique </li></ul></ul>
  25. 28. Question <ul><li>Which technique will the Kepler mission use to search for Earth size planets around other stars? </li></ul><ul><ul><li>A Transits. </li></ul></ul><ul><ul><li>B The astrometric technique. </li></ul></ul><ul><ul><li>C The Doppler related technique. </li></ul></ul><ul><ul><li>D Gravitational lensing. </li></ul></ul>
  26. 29. Question <ul><li>Nearly all the extrasolar planets discovered to date are </li></ul><ul><ul><li>A terrestrial-like planets. </li></ul></ul><ul><ul><li>B jovian-like planets. </li></ul></ul><ul><ul><li>C large, icy worlds. </li></ul></ul>
  27. 30. Is Earth Rare? <ul><li>What are the odds? </li></ul><ul><ul><li>Location, location, location </li></ul></ul><ul><ul><li>Special events </li></ul></ul><ul><li>What are the odds of any special event? </li></ul><ul><ul><li>Example of coin toss </li></ul></ul>
  28. 31. Extraterrestrial Intelligence: Are We Alone? We’ll have to make many (educated) guesses to evaluate odds of ETs in our huge Galaxy But for many guesses we have only a SINGLE data point: our Earth This makes it almost impossible to be “scientific”
  29. 32. A Fearless Estimate Drake “Equation” for the number of “technical civilizations” currently in Milky Way: N = (SFR) x n habit planets x f life x f intel x f tech x L Simple accounting of our ignorance, which increases from left term to right
  30. 33. The Drake Equation – “The great filter” <ul><li>Developed by Frank Drake (pioneer radio astronomer. A semiquanitative attempt to estimate the number of intelligent civilization (N) able to communicate with other civilizations with our galaxy </li></ul><ul><li>N= R  fs  fp  ne  fx  fi  fc  L </li></ul>
  31. 34. R = average rate of star formation in the galaxy <ul><li>R is equal to about 20 stars/year (from recent HST observations of the nebula M 16) </li></ul>
  32. 35. Fs = fraction of stars similar to the sun <ul><li>Fs is probably 10-30% of all stars (stats of spectral type M are too small; type O and B spectral type are too short-lived). The circumstellar disk around the star Beta Pictoris is evidence of planetary formation </li></ul>
  33. 36. Fp = Fraction of stars with planetary systems <ul><li>Fp is now estimated to be relatively high (0.25 – 050). </li></ul>
  34. 37. Ne = mean proportion of planets within the CHZ <ul><li>Ne – proportion of planets within the Continuously Habitable Zone ( assumes liquid water is necessary for life, and planets must have N, O 2 and CO 2 atmospheres) </li></ul><ul><li>Ne approximately 0.1 </li></ul>
  35. 38. Fl = fraction of planets on which life originates <ul><li>Assuming that given enough time organic substances will be synthesized into RNA and DNA, this fraction may be high </li></ul>
  36. 39. Fl = fraction of planets on which life originates <ul><li>In the near future it may be possible to detect indirect evidence for life on extra solar planets by looking for the spectral signature of oxygen and methane in planetary atmospheres. </li></ul>
  37. 40. Fl = proportion of planets with intelligent life <ul><li>Fl = may be near 1 (evolution probably occurs wherever life arises, and intelligence has survival value (Anthropic Principle) </li></ul>
  38. 41. Fc = fraction of intelligent species attempting interstellar communications <ul><li>Interstellar communications requires very advanced technological skills (radio and laser transmitters), plus the expenditure of large amounts of resources. </li></ul>
  39. 42. L = Lifetime of intelligent species <ul><li>We may have to depend upon the “anthropic principle” for guidance </li></ul><ul><li>Doomsday Argument intelligent species may self destruct </li></ul>
  40. 43. Drake Equation Estimate <ul><li>1 – 10,000 advanced civilizations within our galaxy. </li></ul><ul><li>With our present technology it would probably be very difficult to actually detect radio broadcast from another civilization. </li></ul>
  41. 44. ET Question can only be resolved with more data—who is going to make the first move, us or them? <ul><li>Nearest outpost of the hypothesized “galactic club” might be about 100 light-years away </li></ul><ul><li>Within this volume, we already know most of the suitable stars to search for habitable planets. </li></ul><ul><li>With luck, we might even discover strong biosignatures remotely, then send probes </li></ul>
  42. 45. Our 25 nearest stellar neighbors.
  43. 46. What’s a Light Year? <ul><li>This is a DISTANCE not an amount of TIME </li></ul><ul><li>EX: 3 Miles is a distance, 3 Years is a time </li></ul><ul><li>Used to represent extremely LARGE distance in space </li></ul><ul><li>Remember, Light is a Transverse Wave – and all waves travel, they don’t just appear </li></ul>
  44. 47. So how far is it? <ul><li>This distance is very large – it’s hard for the mind to understand how far this is </li></ul><ul><li>Speed of Light = 300,000 km/sec </li></ul><ul><li>That’s about 18,000,000 km/min </li></ul><ul><li>Oh that’s right we don’t like the metric system in America – let’s look at that in mph </li></ul>
  45. 48. So how far is it? <ul><li>Speed of light is about 186,000 miles/sec </li></ul><ul><li>That is about 671,000,000 miles per hour </li></ul>
  46. 49. So how far is it? <ul><li>Now that you know how fast light travels it time think about distance </li></ul><ul><li>If we look at how far light would travel for ONE full year – that distance is a Light Year! </li></ul>
  47. 50. So how far is it? <ul><li>The total distance light travels in one full year is about: 9,460,000,000,000 km (9.46 trillion km) </li></ul><ul><li>In terms of miles that is about: 5,800,000,000,000 miles (5.80 trillion miles) </li></ul>
  48. 51. An example close to home… <ul><li>So how far is that distance of a light year… really. </li></ul><ul><li>EX: it is about 370,000 km from the Earth to the Moon. If you could walk from the Earth to the Moon, how many times would you have to go that distance to equal a light year? </li></ul><ul><li>ANSWER: about 12 MILLION times back and forth from the Earth to the Moon! </li></ul>
  49. 52. 260,000 stars within 250 light years
  50. 53. Pessimists say we have to search almost our entire galaxy to find intelligent company: 200 billion stars offer a lot of possibilities, but typical distances are now tens of thousands of light years!
  51. 54. In that case, why stop with our own Galaxy, since we could reach thousands more, going another factor of 100 further in distance…
  52. 55. What can they do to contact us? <ul><li>Communication is cheapest: </li></ul><ul><li>EM waves such as radio are “easy” for the persistent (e.g. “Species”) (Arecibo can now communicate with a copy of itself on other side of the Milky Way Galaxy!) </li></ul><ul><li>But this is a classic needle-in-a-haystack problem, with so many frequencies, directions, duty cycles, signal patterns, to search. We have to make some assumptions about their transmission, or try “eavesdropping” (really tough!) </li></ul>
  53. 56. Arecibo 1000 foot dish in Puerto Rico, with very powerful radio transmitter
  54. 57. HOLD ON!! Are we SURE we WANT to be Contacted? <ul><li>Are you SURE that all advanced ETs are really “nice” and enlightened? </li></ul><ul><li>What if all of those (bad) Sci-Fi movies were right!?! (as Tim Ferris reminds us) </li></ul><ul><li>But on the other hand, isn’t it more likely that only a PEACEFUL Galactic Club could survive billions of years? </li></ul><ul><li>Would you like to bet the fate of the entire human race that they were wrong? (oops, it’s too late anyway…) </li></ul><ul><li>We must never forget just how ALIEN ETs are going to be! </li></ul>
  55. 58. Even George Lucas can’t imagine how strange ETs will really be, and that is mathematical certainty These are all just humans, dressed up in fancy costumes!
  56. 59. What can they do to contact us? That requires speculating about them! <ul><li>Odds are overwhelming that they will be thousands to millions of years ahead of us, since our technical civilization was just born ---- (how many people in LA are 10sec old?) </li></ul><ul><li>In thousands of years, one-way voyages of colonization should be undertaken by some adventurous explorers (giant space stations are independent of the home star) </li></ul>
  57. 60. If Optimists Correct, Where Are They? <ul><li>They’re uninterested. (Want to talk to ants?) </li></ul><ul><li>1a. Maybe they’re too far away to have received the RECENT ‘news’ of our development of technology </li></ul><ul><li>Remember how LITTLE WE MAY HAVE IN COMMON (besides basic math and physics) </li></ul><ul><li>2. They’re already here, but incompetent or “messing with us”? No–UFO’s internally inconsistent </li></ul><ul><li>3. They are STRICTLY QUARANTINING us new kids on the block (“Zoo Hypothesis”). </li></ul><ul><li>Please credit them with being SERIOUS (unlike USS Enterprise!). </li></ul>
  58. 61. For either possibility 1) or 3), the only sound position is to assume we’re alone for now <ul><li>Until proven otherwise, this may be the only place in the entire Universe where consciousness has developed (we’re only physically insignificant) </li></ul><ul><li>We certainly can’t count on a bunch of super/enlightened beings to swoop down and ‘save’ us just at the brink of some calamity, cures cancer, etc—even if ‘they’ are watching, WE’RE ON OUR OWN </li></ul><ul><li>P.S. MM personally PREFERS it that way! </li></ul><ul><li>(my last night on the telescope) </li></ul>
  59. 62. (Personal) Overview of some of Homo Sapiens’ Highs and Lows What snaps would You send to the Galactic Club? Whatever you say about all these spectacular Highs and Lows, We HUMANS did them 100% on our own No matter how many times we mess up, WE HUMANS will never stop trying I PREFER this to the prospect of some superior aliens doing it all for us