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The formal definition of habitable zone is the distance from the star at which temperatures allow for liquid surface water. Why should we expand this definition? SETI Karen J. Meech, Astronomer Institute for Astronomy A. Habitability can be subsurface, enabled by geothermal heat B. Liquid water is possible on bodies without substantial atmospheres if it is under pressure (sub-surface) C. There are energy sources that allow for liquid water other than the sun D. Habitable zones change with time as a star ages E. A, B and C Overview of Today: Searching for Extraterrestrial Intelligence ! ! ! ! Where and How to Look? Where to look for life How to look for ETI Chances of Success Past, current & future search programs SETI is a Search for ET Intelligence " technology Where to Look – Stellar Lifetimes L/LS Lifetime [yrs] Class Temp [K] 107 O 35,000 108 – 107 B 20,000 – 30,000 109 – 108 HR diagram: is a T sequence Mass (gravity) supported by pressure 109 – 1010 More Mass " more P " higher T " higher energy (L) # 1010 Massive stars " shorter lives A 10,000 – 15,000 F, G 6,000 – 10,000 K, M 3,000 – 6,000 White dwarfs T [K] ! Astronomy review ! ! ! ! Where to Look: Habitable Zones ! Region near star where liquid H2O can exist ! ! Hot stars – wider zone Hot stars – HZ far from star Class Temp [K] L (Lsun) H 2O Freeze H 2O Boil B1 23,000 13,000 173.7 93 A1 9,700 61 11.9 6.4 G2V 5,800 1 1.5 0.8 M5 3,000 0.015 0.19 0.1 The Galactic Habitable Zone Habitable Zone An extension of the concept of the HZ ! ! The region(s) of the Milky Way that allow complex biological life to emerge • • • • ! Massive stars " supernovae Release of dangerous radiation (not habitable) – red Early on – not enough heavy elements for planets – blue Green – optimal conditions for life Evolution of the HZ ! ! ! Stellar luminosity increases HZ moves outward as star’s T rises Planet atmosphere composition changes Some requirements for complex life in the Galaxy: ! Located in a region with few transient radiation events, such as supernovae ! ! ! ! HZ of Stars ! Depletion of ozone Low-mass planets in the HZ are tidally-locked to their host stars ! Enough metallicity, or building blocks for terrestrial planets Enough time for biological evolution ! ! Like the moon around the Earth One side always hot, the other always cold A planet orbiting a medium mass star in the HZ is not tidally locked Binary Star Systems The Galactic Habitable Zone Two predictions ! Stellar center of mass Lineweaver et al. (2004) Majority of habitable planets between 7-9 kpc, expanding outwards with time. ! Gowanlock et al. (2011) Majority of habitable planets in the inner Galaxy, expanding with time, but entire disk suitable. Schematic of a planet in a binary star system a) The planet orbits one component of the binary b) The planet is in a circumbinary orbit about both stellar components From: Perryman 2011 Image: Astronomy Now magazine, Dec. 2011 Where to Look – Binaries?? Where to Look – Binaries? ! Planets have been detected orbiting in binary star systems ! ! ~50% of stars in the Milky Way are binary systems Factors influencing habitability ! Eccentricity ! Temperature ! Dynamic stability ! ! ! ! ! Cephei – First binary system with a planet 1.59MSun (K1IV), 0.4MSun (M1) Period = 74 yr, e = 0.44 ! Planet 1.76MJup, e = 0.2 ! Stable if in resonance ! ! ! ! How circular are the orbits of planets? How does the temperature of planets change with time? How do the orbits of planets change with time? Will planets be retained in binary systems over long periods? Free floating planets have been detected Class Discussion ! Why do you think that planets in binary star systems could have habitable planets? Where to Look: Extrasolar Planets To date, there have been > 1000 confirmed exoplanets Including the Kepler candidates, there are over 3000 exoplanet detections Statistics show that maybe 70% of stars might have planets ! ! ! ! 185 stars with planets out to 150 LY How: Manifestations of Advanced Civilizations Where to Look – Summary ! Rule out hot stars: OBA ! Rule out cool stars?? M ! ! Best F, G, K Stars Lifetime too short HZ too small ! But . . . These are the most numerous stars . . . ! ! Binaries? ! Possible, but not first choice We ve Already Sent Messages # stars ! ! ! ! Invention of TV – 1940 s (~70 yrs ago) EM radiation travels out to 70 LY 50% of power is narrow (0.1Hz) carrier wave 50% of power is the picture ! 1 AU How far has our TV signal travelled? = 1.5 LY ! Our stellar neighborhood ! ! ! Oort Dyson Spheres Cloud ! ! ! Oort cloud ~ 100,000 AU = 1.5 LY Local stellar density ~ 0.004 stars / cubic LY In 2013 the signal has passed ~ 6500 stars http://workshop.chromeexperiments.com/stars/ Builds structure surrounding star at HZ distance ! Collects all solar energy ! Only IR / radio escape ! ! ! 77 ! 25 LY Interstellar Travel ! ! ! ! ! ! ! ! ! ! 80 years ! Lack technology 10 years Fuel costs ~ $1015 (106 billion = quadrillion) Cooling requires 2x103 km array Scoop of 100 km radius Not invented! Characteristics of Effective Communication ! ! ! ! ! Expensive ( millennia of the world GNP) Uninvented Technologies?? ! ! ! Smaller cost per probe Send 106 probes (to get big enough star system sample) Launching 1/day " 3000 years! Cost $1013 Info sent by radio " many 100m class radio telescopes Why send a probe? Just listen! Ramjets – collect fuel from ISM ! ! ! Photon (matter-antimatter) ! Eavesdrop on another civilization ! v=30 km/s - to " Cen – 40,000 yr! Cryogenic suspension? Generations? Nuclear ! Space Probes – Cheaper Alternative? ! Chemical rockets ! A variant – Ringworld LY Types of Searches – Interstellar Travel ! Advanced civilization Requires minimum E over background noise Travel at the speed of light Not deflected by stellar magnetic fields Easy to generate, beam & detect Not be absorbed by ISM ! 1-10 GHz – low noise ! Recall c = #f H radiates at 1.42 GHz (# = 21 cm) ! OH at 1.6-1.72 GHz ! Cosmic Water Hole !. But millions of frequencies are still possible . . . . ! ! EM Radiation No Mass No Charge Specific Wavelengths Where to Search in the EM Spectrum – The Water Hole Probability of Success? The Drake Equation ! ! ! ! ! ! ! ! Nciv N* fp np fl fi fc Lc Number of detectable civilizations Number of stars now Fraction forming planets Fraction suitable for life Fraction where life exists Fraction with intelligence Fraction with communication Probability of survival ! Number of stars now R = 10 yr-1 ! ! ! ! ! Stars form out of clouds of gas & dust Process ~ well understood We have a good observed number for local rate of star formation (R*) over time At least 100 billion stars in the Milky Way Number of stars is related to the star formation rate N* = Sum of R* over time Nciv = N* x fp x np x fb x fc x fi x fc x Lc Illingworth, et al. (UCLO) Fraction Forming Planets ! How Many are Habitable? ! By Star type ! fp = 0.2-0.9 ! ! ! ! ! ! ! Rate of hot Jupiters – 0.75% Rate of Jupiter-mass objects inside 3.5 AU – 7% 1-1.5% sunlike stars have gas giants Mostly finding Jupiter-mass to date " must have smaller planets too True rate must be much higher! ! 40% of stars may have low mass planets New Kepler discoveries " 1200 planets! ! Fraction With Life ! Organics in space are ubiquitous Miller-Urey Experiments ! Hydrothermal vents ! Life occurred early on the Earth ! ! Extrasolar Planet Searches ! ! Organics + water + energy " amino acids Oceans + internal planetary heat ! Rocky planet occurrence ! np = 0.01-0.5 M stars: small zones, but very abundant F stars: much larger HZ ! 23% of stars host super Earths with P < 50 days (Howard et al. 2010) 17.4% of stars have planets with M < 10 Mearth (Wittenmyer et al. 2011) ! Fraction with Intelligence? ! Studies of language " markers of intelligence ! ! ! ! ! Information theory Complexity of communication Ability to make tools / problem solve Brain to body mass ratio Many factors may be indicative of intelligence fl = 0.001-0.01 fi = 0.001-0.01 Animal Communication Complexity Fraction with Technology ! Species Communication Entropy Repertoire Size Monkey Social behavior 6.9 120 Whistles 6.67 102 Alphabet " char (english) 4.8 26 Chinese 11.6 3000 Bottlenose dolphin Homosapien ! ! fc = 0.1-0.9 Survival? ! Homo sapiens has been around for ~ 3 million yrs (Australopithicine) Technology – 100 yrs Inevitable? ! Survival? Mean lifetime of a civilization or fraction which endures a long enough time to be detected. “The receipt of a message from an advanced civilization will show that there are advanced civilizations, that there are methods of avoiding the self-destruction that seems so real a danger of our present technological adolescence. Finding a solution to a problem is helped enormously by the certain knowledge that a solution exists. This is one of many curious connections between the existence of intelligent life elsewhere and the existence of intelligent life on Earth.” Carl Sagan Lc = 10-5-0.01 Meanings Evaluating the Drake Equation Variable Pessimist N* Optimist Description 100 billion 100 billion Num of stars in MW fp 0.2 0.9 Fraction of stars form planets np 0.01 0.5 Fraction w/ habitable planets fl 0.001 0.01 Existence of Life fi 0.001 0.01 Rise of Intelligence fc 0.001 0.9 Rise of technology Lc 0.00001 0.01 Survival/duration now Total 0.000002 50500 Communicating civilizations now ! ! ! Pessimist: 106 LY between civilizations Optimist: 16 LY " lots of neighbors! ! Optimist ! Curiosity is by product of intelligence ! Laws of physics same everywhere Pessimist ! Consider development 104-109 yrs ago! No communication! Frank Tipler Proof why there are no other civilizations Optimistic vs. Pessimistic Views ! Optimist ! ! ! ! ! Curiosity is the by product of intelligence Laws of physics same everywhere: might give rise to intelligent life everywhere Life occurred early on the Earth and lead to intelligent life Many planets detected in the Milky Way ! ! ! Pessimist ! ! ! Tipler Argument We’ve only been able to send signals for ~100 years It is not clear that technology does not lead to self-destruction (e.g. the cold war) Fred Hoyle: “The chance that higher life forms might have emerged in this way is comparable to the chance that a tornado sweeping through a junkyard might assemble a Boeing 747 from the materials therein.” ! ! Arguments Against Tipler ! Pre-Copernican comparison ! ! The Zoo Hypothesis ! ! ! We took a long time to learn we are not the center of the solar system, why the only ones in the galaxy? There are advanced civilizations They leave us alone to develop ( prime directive ) Seti scientist N. Cohen How do we know Frank Tipler exists? Have you ever seen him? There are 4 billion people on this planet, surely an intelligent creature would find some direct way of making his presence known to a sizeable fraction of the planet. . . ! ! ! 1600 Feb 17, Rome " burned at stake for heresy There are an infinite number of other worlds, and life exists on them ! Mathematician Gauss ! 1820 s ! Communication scheme for inhabitants on Moon ! Tree arrangement in Siberia " pythagorean theorem. They do not exist ! Von Neumann machines Pre-Copernican comparison ! ! We took a long time to learn we are not the center of the solar system, why the only ones in the galaxy? The Zoo Hypothesis ! ! There are advanced civilizations They leave us alone to develop ( prime directive ) ! Rare Earth Hypothesis ! Astrophysical explanation: major catastrophes ! ! ! Complex life is rare, microbial life may be abundant The timescales for life extinguishing events like gamma ray bursts is roughly the same timescale that it takes for intelligent life to arise Threats from supernovae and close planetary system encounters Project Ozma ! Giordano Bruno ! The Great Silence Early SETI ! ! Will explore galaxy in 300 x 106 yr No evidence on Earth ! Take the optimistic path for # civilizations No technology " sophisticated ~ 100 yr Older societies " more advanced Advanced societies will have interstellar travel 1959 Phil Morrison " First SETI article It is difficult to estimate the chances of success, but if we don t try the chances are zero ! 85 ft NRAO dish in West VA ! ! 2 nearby stars Strange noise pulses " terrestrial interference Star Dist [pc] Type PM [ /yr] $ Ceti 3.46 G8V 1.92 % Eri 3.28 K2V 0.98 Unraveling the Mystery 1967 Galactic Radio Survey ! ! ! ! ! ! Mysterious repeated pulsed ratio signals Repeat every 1.33730115 sec Pulse duration 0.001 s Regular LGM signals ! ! ! ! A New physical phenomenon ! A new physical phenomenon " the Discovery of Pulsars ! Small Source Size: New object! ! J. Bell discovered the signal (grad student) A. Hewitt got the nobel prize ! Finite speed of light " cannot have infinitely thin pulse Small source ! Energy spread over many f " expensive No doppler effect " not from orbiting planet Knew distance of object ! Example: ! ! ! 1 2 Source 3 x 105 km diam Turn off instantaneously Light from 1 takes longer than from 2 to reach earth Signal strength " 109 more than Earth s E output " not artificial!! vel x time = dist; d / v = t 3x105 / 3x105 = 1 sec Drake Puzzle Solution What is the Message? ! ! ! ! ! ! First US SETI meeting (11/1961) Drake passed out a test to participants Language would not be sent " picture Encode a picture in 1 s and 0 s ! ! ! ! ! 551 numbers Divisible by prime #s 29 x 19 or 19 x 29 Other Early Efforts ! 1974 Cornell Arecibo Antenna ! Message to Hercules cluster ! 25,000 LY away ! 300,000 stars ! Binary ! 001 ! 010 ! 011 ! 100 ! 101 ! 110 ! 111 ! 1000 ! 1 2 3 4 5 6 7 8 ! Left column Sun & planets Bottom Center Human R: Next to planets – populations #2 has 11 (expedition?) #3 has 3000 (colony?) ! #4 has 7 billion ! ! ! Top: C and O (C-based life) Other Early Efforts Adenine ! Cytocene Voyagers 1 & 2 ! Guanine Thymine ! 1983 6/13 Pioneer 10 ! ! Solar System Gold disks with greetings, music First to leave Solar System Gold Plaque Scale of spacecraft & humans Solar system & Earth ! 3D pulsar map of location ! Arecibo Antenna Human Genome ! SETI Search Space A Variety of Searches Date Observer Observatory # or Freq Targets ! Drake NRAO 1.42 GHz % Eri, $ Tau 1968 Troitsky Gorky 21, 30 cm 12 solar stars 1972 Verschuur NRAO 1.42 GHz 10 nearby stars ! 1972 Troitsky Gorky 16, 30, 50 cm All sky ! 1972-6 Palmer, Zuckerman NRAO 21 cm 670 nearby stars 1972 Kardashev Europe Several All sky 1973- Dixon, Cole Ohio 21 cm All sky 1974 Bridle, Feldman Algonquin 1.3 cm 70 nearby stars 1975-6 Drake, Sagan Arecibo 12.5, 18, 21 cm Nearby galaxies 1977 Tarter NRAO 18 cm 200 nearby stars 1978 Horowitz Arecibo 21 cm 185 nearby stars 1983 Horowitz Harvard 1.42 GHz All Sky 1985 Horowitz META 1.42 GHz All Sky Fraction of Sky covered Sensitivity of Search ! Number of frequencies Planetary Society & SETI ! ! ! Begun in 1981 – Targeted & All Sky ! 131,000 channels 1.42 GHz ! META (1985) ! ! ! ! 131,000 channels 200 stars Sentinal – continuation of Suitcase SETI ! ! The NASA Search Suitcase SETI – Horowitz (1983) ! ! ! ! ! ! ! Billion-channel Extra-Terrestrial Assay 109 channels ! The NASA Search Targeted Program ! ! ! ! ! ! 300-1000s per star 107 frequencies Centered on 1.42 GHz, 1-3 GHz 770 Solar type stars Within 22 LY Good candidates for planets Use Arecibo ! All Sky Survey ! ! ! Use 34-m DSN dishes Scan entire sky (3-5 yrs) 107 channels, 1-10 GHz If they existed, they would be here by now Sagan – talked him out of objections (Drake Eqn) Senate budget approved SETI in 1982 Renamed from SETI to HRMS (High Resolution Microwave Survey) In 1993 ! ! Budget of $2,000,000/ yr Senator Proxmire – cut funding in 1981 ! Megachannel Extra-Terrestrial Assay 8x106 channels Very sensitive – Energy of Earth could be detected out to 1000 LY BETA (1995) ! ! Each survey has been limited 1960 Richard Bryan - Nevada senator eliminated all NASA funding for SETI SETI was only 0.1% of NASA’s annual budget, or a nickel per taxpayer So, SETI Is Not ! ! ! ! An investigation of UFO s or alien abductions A religion, or a cult Politically correct Dawn of public-private partnerships within Astrobiology? ! Project Phoenix ! SETI Institute: Allen Telescope Array • 1000 nearby sun-like stars from 1995-2004 • 200 stars in Southern hemisphere • 11000 hours; 240 light years ! "#$%"$&$'()*$% ! +,-%'./01%2.'#$'% ! 3456&%7)%8-9%1:% ! • 1 – 3 GHz • Realtime signal detection and follow up • Pioneer 10: signal beyond Solar System ;)(67$2%67%<67%=>$$?@%=A% ! B5C&.(0*>.D67$%*6>7E$>'#.*%% ! F$'.GE%H%()E'7>5(7.)E%I5E2'%>6.'$2% *>.D67$&J% ! B65&%A&&$E%#6'%2)E67$2%K+-%1.&&.)E% ! A(($''%I)>%7#$%G$E$>6&%'(.$E7.L(% ()115E.7J% ! Berkeley ! Optical SETI ! Enhanced • “Alien” Laser signals: continuous or pulse ! SKA • More efficient, narrower beam, bright ! Phoenix • Several searches: Harvard, Berkeley, Lick.. ! ! ! ! ! ! ! ! We Transmit? Not yet? Could we be the youngest technology in the galaxy? We are currently leaking Transmission is a long term strategy We are culturally too immature Who will speak for Earth? What will they say? Organizations: ! U " nited Nations Committee on the Peaceful Uses of Outer Space ! ! International Institute of Space Law International Academy of Astronautics ! ! Timelines ATA Allen Telescope Array ! ! ATA • No “waterhole”; unique absorption lines ? ! Should Exploration Of The Galaxy ! SKA Square kilometer array ! collaboration between ~10 countries ! for Active SETI ! If we transmit a signal to all known stars, how many could we receive a response within the following time durations ! ! ! 10 years ! A signal could travel to and from a star within a distance of 5 light yrs ! There are only 3 stars within 5 light years 40 years ! The volume is (43) 64 times larger than that of 10 years ! There are ~100 stars within 20 light years 100 years ! ~0.00323 stars per cubic light year in the solar neighborhood ! Distance is 50 light years ! Volume of a sphere: (4/3)*pi*503 ! ~1700 stars or 1 out of every 100 million stars in the Galaxy ! Timelines ! for Active SETI 1000 years: ! ! ! Citizen ! SETI efforts can be helped using the SETI@Home distributed computing platform ! The platform uses your unused CPU cycles to process radio telescope data 1.7 million stars within 500 light years About 1 in every 100,000 stars in the Milky Way ! ! ! "#$%*>)C6C.&.7J%)I%'5(($''% ! %.'%2.M(5&7%7)%$'7.167$@%C57%.I%N$% E$D$>%'$6>(#%7#$%(#6E($%)I%'5(($''%.'% O$>)P% ! 0%=)(()E.%H%Q)>>.')E% Science With cheap multicore machines, there is a lot of underutilized computation time Currently has over 3 million users