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Home , Active SETI, Allen Telescope Array, Galactic habitable zone, Rare Earth (book), Water hole (radio)

The formal definition of habitable zone is the distance from the at which temperatures allow for liquid SETI surface water. Why should we expand this definition?

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 D. Habitable zones change with time as a star ages E. A, B and C

Overview of Today: Searching for Where and How to Look? Extraterrestrial Intelligence

! Where to look for ! How to look for ETI ! Chances of Success ! Past, current & future search programs

SETI is a Search for ET Intelligence " technology

Where to Look – Where to Look: Habitable Zones Stellar Lifetimes ! L/LS Region near star where Lifetime Class Temp [K] liquid H O can exist [yrs] 2 ! Hot – wider zone White dwarfs 7 10 O 35,000 ! Hot stars – HZ far from star

T [K] 108 – 107 B 20,000 – 30,000 ! Astronomy review 109 – 108 A 10,000 – Class Temp [K] L (Lsun) H2O H2O ! HR diagram: is a T sequence 15,000 Freeze Boil ! Mass (gravity) supported by pressure B1 23,000 13,000 173.7 93 109 – 1010 F, G 6,000 – ! More Mass " more P " higher T " 10,000 A1 9,700 61 11.9 6.4 higher energy (L) 10 G2V 5,800 1 1.5 0.8 ! Massive stars " shorter #10 K, M 3,000 – 6,000 M5 3,000 0.015 0.19 0.1 The Habitable Zone

! An extension of the concept of the HZ ! The region(s) of the that allow complex biological life to emerge ! Evolution of the HZ • Massive stars " supernovae ! Stellar luminosity increases • Release of dangerous radiation (not habitable) – red ! • Early on – not enough heavy elements for – blue HZ moves outward as star’s T rises • Green – optimal conditions for life ! atmosphere composition changes Some requirements for complex life in the : ! Located in a region with few transient radiation events, ! HZ of Stars such as supernovae ! Low-mass planets in the HZ are tidally-locked to their host stars ! Depletion of ozone ! Like the moon around the Earth ! Enough , or building blocks for terrestrial planets ! One side always hot, the other always cold ! Enough time for biological evolution ! A planet orbiting a medium mass star in the HZ is not tidally locked

The Galactic Habitable Zone Systems

Two predictions Stellar center of mass

! Lineweaver et al. (2004)

Majority of habitable pla- nets between 7-9 kpc, expanding outwards with time.

! Gowanlock et al. (2011)

Majority of habitable pla- Schematic of a planet in a binary star system nets in the inner Galaxy, a) The planet orbits one component of the binary expanding with time, but b) The planet is in a circumbinary orbit about both stellar components entire disk suitable.

Image: Astronomy Now magazine, Dec. 2011 From: Perryman 2011

Where to Look – Where to Look – Binaries? Binaries?? ! Planets have been detected orbiting in binary star systems ! ~50% of stars in the Milky Way are binary systems ! Factors influencing habitability ! Eccentricity ! How circular are the orbits of planets? ! Temperature ! How does the temperature of planets change with time? ! Dynamic stability ! How do the orbits of planets change with time? ! ! Cephei – First binary system with a planet ! Will planets be retained in binary systems over long periods? ! Free floating planets have been detected ! 1.59MSun (K1IV), 0.4MSun (M1) ! Period = 74 yr, e = 0.44

! Planet 1.76MJup, e = 0.2 ! Stable if in resonance Class Discussion Where to Look: Extrasolar Planets

! Why do you think that planets in binary star systems could ! To date, there have been > 1000 confirmed have habitable planets? ! Including the Kepler candidates, there are over 3000 detections ! Statistics show that maybe 70% of stars might have planets

!185 stars with planets out to 150 LY

How: Manifestations of Where to Look – Summary Advanced Civilizations

! ’ ! Rule out hot stars: OBA ! Best F, G, K Stars Invention of TV – 1940 s (~70 yrs ago) ! Lifetime too short ! EM radiation travels out to 70 LY ! Rule out cool stars?? M ! 50% of power is narrow (0.1Hz) carrier wave ! HZ too small ! 50% of power is the “picture” ! But . . . These are the most numerous stars . . . ! Binaries? ! Possible, but not first choice

We’ve Already Sent Messages

# stars How far has our TV signal travelled? Dyson Spheres !1 AU = 1.5 LY

! Our stellar neighborhood ! ~ 100,000 AU = 1.5 LY ! Advanced civilization ! Local stellar density ~ 0.004 stars / cubic LY ! Builds structure !Oort Cloud ! In 2013 the signal has passed ~ 6500 stars surrounding star at HZ ! http://workshop.chromeexperiments.com/stars/ distance ! Collects all solar energy ! Only IR / escape ! A variant – “Ringworld”

!77 LY

!25 LY

Types of Searches – Interstellar Travel Space Probes – Cheaper Alternative?

! Interstellar Travel ! Eavesdrop on another civilization ! Chemical rockets ! Smaller cost per probe ! v=30 km/s - to " Cen – 40,000 yr! ! Cryogenic suspension? Generations? ! Send 106 probes (to get big enough star system sample) ! Nuclear ! Launching 1/day " 3000 years! ! 80 years ! Cost $1013 ! Photon (matter-antimatter) ! Lack technology ! Info sent by radio " many 100m class radio telescopes ! 10 years ! Why send a probe? Just listen! ! Fuel costs ~ $1015 (106 billion = quadrillion) ! Cooling requires 2x103 km array ! Ramjets – collect fuel from ISM ! Scoop of 100 km radius ! Expensive (“millennia” of the world GNP) ! Uninvented Technologies?? ! Not invented!

Characteristics of Effective Where to Search in the EM Communication Spectrum – The “”

! Requires minimum E over background noise ! 1-10 GHz – low noise ! Travel at the speed of light ! Recall c = #f ! Not deflected by stellar ! H radiates at 1.42 GHz magnetic fields (# = 21 cm) ! Easy to generate, beam & detect ! OH at 1.6-1.72 GHz ! Not be absorbed by ISM ! Cosmic “Water Hole” EM Radiation !. But millions of frequen- No Mass cies are still possible . . . . ! No Charge Specific Wavelengths Probability of Success? !Number of stars now The R = 10 yr-1 ! Nciv Number of detectable civilizations * ! N Number of stars now ! Stars form out of clouds of gas & dust ! fp Fraction forming planets ! Process ~ well understood ! np Fraction suitable for life ! We have a good observed number for local rate of (R*) over time ! fl Fraction where life exists ! At least 100 billion stars in the Milky Way ! fi Fraction with intelligence ! Number of stars is related to the star ! fc Fraction with communication formation rate ! Lc Probability of survival

* 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 !How Many are Planets Habitable?

! By Star type ! M stars: small zones, but very abundant ! F stars: much larger HZ f = 0.2-0.9 ! Extrasolar Planet Searches p ! ! Rate of hot Jupiters – 0.75% Rocky planet occurrence ! 23% of stars host super Earths with P < 50 days ! Rate of Jupiter-mass objects inside 3.5 AU (Howard et al. 2010) – 7% n = 0.01-0.5 ! 17.4% of stars have planets with M < 10 Mearth ! 1-1.5% sunlike stars have gas giants p (Wittenmyer et al. 2011) ! 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 !Fraction With Life Intelligence?

! Studies of language " markers of intelligence ! Organics in space are ubiquitous ! Information theory ! Miller-Urey Experiments ! Complexity of communication ! Organics + water + energy " amino acids ! Ability to make tools / problem solve ! Hydrothermal vents ! Brain to body mass ratio ! Oceans + internal planetary heat ! Many factors may be indicative of intelligence ! Life occurred early on the Earth fl = 0.001-0.01

fi = 0.001-0.01

Animal Communi- Fraction with Technology cation Complexity

! Homo sapiens has been around for ~ 3 million yrs (Australopithicine) Species Communication Entropy Repertoire ! Technology – 100 yrs Size ! Inevitable? Monkey Social behavior 6.9 120

Bottlenose Whistles 6.67 102 dolphin Homosapien Alphabet " 4.8 26 char (english) f = 0.1-0.9 Chinese 11.6 3000 c

Survival? !Survival?

! Mean lifetime of a civilization or fraction which endures a long “The receipt of a message from an advanced civilization will show that enough time to be detected. 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

-5 Lc = 10 -0.01

Meanings Evaluating the Drake Equation

Variable Pessimist Optimist Description * N 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 f 0.001 0.01 Existence of Life l ! Optimist

fi 0.001 0.01 Rise of Intelligence ! is by product of intelligence fc 0.001 0.9 Rise of technology ! Pessimist: 106 LY ! Laws of physics same L 0.00001 0.01 Survival/duration now c between civilizations everywhere Total 0.000002 50500 Communicating civilizations now ! Pessimist ! Optimist: 16 LY " lots ! Consider development 104-109 of neighbors! yrs ago! No communication! Optimistic vs. Pessimistic Views Frank Tipler “Proof why there are ! Optimist ! Curiosity is the by product of intelligence no other civilizations” ! Laws of physics same everywhere: might give rise to intelligent life everywhere ! Tipler Argument ! Will explore galaxy in 300 x 6 ! Life occurred early on the Earth and lead to intelligent life ! Take the optimistic path for # 10 yr civilizations ! Many planets detected in the Milky Way ! No evidence on Earth ! No technology " ! Von Neumann machines ! Pessimist sophisticated ~ 100 yr ! We’ve only been able to send signals for ~100 years ! Older societies " more ! They do not exist ! It is not clear that technology does not lead to self-destruction advanced (e.g. the cold war) ! Advanced societies will have interstellar travel ! : “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 The Great Silence

! Pre-Copernican comparison ! Pre-Copernican comparison ! We took a long time to learn we are not the center of the solar ! We took a long time to learn we are not the center of the solar system, why the only ones in the galaxy? system, why the only ones in the galaxy? ! The “” ! The Zoo Hypothesis ! There are advanced civilizations ! There are advanced civilizations ! They leave us alone to develop (“prime directive”) ! They leave us alone to develop (“prime directive”) ! Seti scientist N. Cohen ! ! Complex life is rare, microbial life may be abundant “How do we know Frank Tipler exists? Have you ever ! Astrophysical explanation: major catastrophes seen him? There are 4 billion people on this planet, ! The timescales for life extinguishing events like gamma ray bursts is surely an intelligent creature would find some direct way roughly the same timescale that it takes for intelligent life to arise of making his presence known to a sizeable fraction of ! Threats from supernovae and close encounters the planet. . .”

Early SETI

! 1959 Phil Morrison " First SETI article “It is difficult to estimate the chances of success, but if we don’t try the ! Giordano Bruno ! Mathematician Gauss chances are zero” ! 1600 Feb 17, Rome " burned ! 1820’s at stake for heresy ! 85 ft NRAO dish in West VA ! Communication scheme ! “There are an infinite number of ! 2 nearby stars Star Dist Type PM [“/yr] other worlds, and life exists on for inhabitants on Moon ! Strange noise pulses " [pc] them” ! Tree arrangement in terrestrial interference $ Ceti 3.46 G8V 1.92 Siberia " pythagorean theorem. % Eri 3.28 K2V 0.98 1967 Galactic Radio Survey Unraveling the Mystery

! Small Source Size: New object! ! Mysterious repeated pulsed ! Finite speed of light " cannot have ratio signals infinitely thin pulse ! Repeat every 1.33730115 sec ! Small source ! A New physical phenomenon ! Example: ! Pulse duration 0.001 s 1 2 ! Source 3 x 105 km diam ! Regular “LGM” signals ! Energy spread over many f " expensive ! Turn off instantaneously ! A new physical phenomenon ! Light from 1 takes longer than from 2 ! No doppler effect " not from " the Discovery of to reach earth orbiting planet ! J. Bell discovered the signal ! Knew distance of object (grad student) ! Signal strength " 109 more than ! A. Hewitt got the nobel prize Earth’s E output " not artificial!!

vel x time = dist; d / v = t 3x105 / 3x105 = 1 sec

What is the Message? Drake Puzzle Solution

! Left column ! Sun & planets ! Bottom Center ! First US SETI ! “Human” meeting (11/1961) ! Binary ! Drake passed out a ! 001 1 ! R: Next to planets – populations test to participants ! 010 2 ! #2 has 11 (expedition?) ! 011 3 ! #3 has 3000 (colony?) ! “ ” Language would ! 551 numbers ! 100 4 ! #4 has 7 billion not be sent " picture ! 101 5 ! Divisible by prime #s ! Top: C and O (C-based life) ! Encode a picture in ! 110 6 ! 29 x 19 or 19 x 29 1’s and 0’s ! 111 7 ! 1000 8

Other Early Efforts Other Early Efforts

! 1974 Cornell Adenine ! Voyagers 1 & 2 Cytocene ! Arecibo ! Gold disks with greetings, ! Message to cluster Guanine music Thymine ! 25,000 LY away ! 1983 6/13 Pioneer 10 ! 300,000 stars ! First to leave Solar System Solar System ! Gold Plaque ! Scale of spacecraft & humans Arecibo Antenna ! Solar system & Earth ! 3D map of location

Human Genome A Variety of Searches SETI Search Space

Date Observer Observatory # or Freq Targets ! Each survey has been 1960 Drake NRAO 1.42 GHz % Eri, $ Tau limited 1968 Troitsky Gorky 21, 30 cm 12 solar stars 1972 Verschuur NRAO 1.42 GHz 10 nearby stars ! Fraction of Sky covered 1972 Troitsky Gorky 16, 30, 50 cm All sky ! Sensitivity of Search 1972-6 Palmer, Zuckerman NRAO 21 cm 670 nearby stars ! Number of frequencies 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 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

Planetary Society & SETI The NASA Search ! Suitcase SETI – Horowitz (1983) ! 131,000 channels ! Begun in 1981 – Targeted & All Sky ! 200 stars ! Sentinal – continuation of Suitcase SETI ! Budget of $2,000,000/ yr ! 131,000 channels 1.42 GHz ! Senator Proxmire – cut funding in 1981 ! META (1985) ! “If they existed, they would be here by now” ! Megachannel Extra-Terrestrial Assay ! Sagan – talked him out of objections (Drake Eqn) 6 ! 8x10 channels ! Senate budget approved SETI in 1982 ! Very sensitive – Energy of Earth could be detected out to 1000 LY ! Renamed from SETI to HRMS (High Resolution Microwave Survey) ! BETA (1995) ! In 1993 ! Billion-channel Extra-Terrestrial Assay ! 109 channels ! 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

The NASA Search So, SETI Is Not !

! An investigation of UFO’s or alien ! Targeted Program ! All Sky Survey ! 300-1000s per star ! Use 34-m DSN dishes abductions ! 107 frequencies ! Scan entire sky (3-5 yrs) ! A religion, or a cult ! Centered on 1.42 GHz, 1-3 GHz ! 107 channels, 1-10 GHz ! 770 Solar type stars ! Politically correct ! Within 22 LY ! Good candidates for planets ! Use Arecibo

Dawn of public-private partnerships within ? !Project !SETI Institute:

• 1000 nearby sun-like stars from 1995-2004 ! "#$%"$&$'()*$% • 200 stars in Southern hemisphere ! +,-%'./01%2.'#$'% • 11000 hours; 240 light years ! 3456&%7)%8-9%1:% • 1 – 3 GHz ! ;)(67$2%67%<67%=>$$?@%=A% • Realtime signal detection and follow up ! B5C&.(0*>.D67$%*6>7E$>'#.*%% • Pioneer 10: signal beyond Solar System ! 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 Exploration Of The Galaxy

• “Alien” Laser signals: continuous or pulse !SKA ! ATA • More efficient, narrower beam, bright ! Allen Telescope Array !ATA • No “waterhole”; unique absorption lines ? ! SKA • Several searches: Harvard, Berkeley, Lick.. !Phoenix ! Square kilometer array ! collaboration between ~10 countries

!Should We Transmit? !Timelines for Active SETI

! Not yet? !If we transmit a signal to all known stars, how many could we ! Could we be the youngest technology in the galaxy? receive a response within the following time durations ! We are currently “leaking” ! 10 years ! Transmission is a long term strategy ! A signal could travel to and from a star within a distance of 5 light yrs ! We are culturally too immature ! There are only 3 stars within 5 light years ! Who will speak for Earth? ! 40 years 3 ! What will they say? ! The volume is (4 ) 64 times larger than that of 10 years ! There are ~100 stars within 20 light years ! Organizations: ! 100 years ! "United Nations Committee on the Peaceful Uses of ! ~0.00323 stars per cubic light year in the solar neighborhood ! International Institute of Space Law ! Distance is 50 light years ! International Academy of Astronautics ! 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 !Citizen Science

! 1000 years: ! SETI efforts can be helped using the ! 1.7 million stars within 500 light years SETI@Home distributed computing platform ! About 1 in every 100,000 stars in the Milky Way ! The platform uses your unused CPU cycles to process data ! With cheap multicore machines, there is a lot of underutilized computation time

! Currently has over 3 million users

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