SETI. Where and How to Look? Where to Look: Habitable Zones. Overview of Today: Searching for Extraterrestrial Intelligence

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1 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, B 20,000 30, HR diagram: is a T sequence Mass (gravity) supported by pressure 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, A1 9, G2V 5, M5 3,

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

optimal conditions for life Evolution of the HZ Stellar luminosity increases HZ moves outward as star s T rises Planet atmosphere composition

Depletion of ozone Low-mass planets in the HZ are tidally-locked to their host stars Enough metallicity, or building blocks for terrestrial planets

in the HZ is not tidally locked Binary Star Systems The Galactic Habitable Zone Two predictions Stellar center of mass Lineweaver et al.

(2011) Majority of habitable planets in the inner Galaxy, expanding with time, but entire disk suitable.

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

2 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 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

3 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 Where to Look Summary Rule out hot stars: OBA Best F, G, K Stars Lifetime too short Rule out cool stars?? M HZ too small But... These are the most numerous stars... Binaries? Possible, but not first choice How: Manifestations of Advanced Civilizations 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 We ve Already Sent Messages # stars

1 AU How far has our TV signal travelled?

Dyson Spheres Cloud Oort cloud ~ 100,000

? Smaller cost per probe Send 106 probes

Nuclear Space Probes Cheaper Alternative?

4 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 ~ stars / cubic LY In 2013 the signal has passed ~ 6500 stars Advanced civilization 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 Builds structure surrounding star at HZ distance Collects all solar energy Only IR / radio escape 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 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

detectable civilizations Number of stars now Fraction

life exists Fraction with intelligence Fraction with

R = 10 yr-1 Stars form out of clouds of gas & dust Process

rate of star formation (R*) over time At least 100 billion

star formation rate N* = Sum of R* over time Nciv = N* x

(UCLO) Fraction Forming Planets How Many are Habitable?

75% Rate of Jupiter-mass objects inside 3.5 AU 7% 1-1.

Jupiter-mass to date " must have smaller planets too True

planets New Kepler discoveries " 1200 planets Fraction

Hydrothermal vents Life occurred early on the Earth np = 0.

internal planetary heat M stars: small zones, but very

23% of stars host super Earths with P < 50 days (Howard et

4% of stars have planets with M < 10 Mearth (Wittenmyer et

With Life Extrasolar Planet Searches Studies of language "

5 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 = 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 Organics in space are ubiquitous Miller-Urey Experiments Hydrothermal vents Life occurred early on the Earth np = Organics + water + energy " amino acids Oceans + internal planetary heat M stars: small zones, but very abundant F stars: much larger HZ Rocky planet occurrence 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? With Life Extrasolar Planet Searches 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 = fi =

$civilization or fraction$ which endures a long enough

6 Animal Communication Complexity Fraction with Technology Species Communication Entropy Repertoire Size Monkey Social behavior Whistles Alphabet " char (english) Chinese Bottlenose dolphin Homosapien fc = 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 = Meanings Evaluating the Drake Equation Variable Pessimist N* Optimist Description 100 billion 100 billion Num of stars in MW fp Fraction of stars form planets np Fraction w/ habitable planets fl Existence of Life fi Rise of Intelligence fc Rise of technology Lc Survival/duration now Total 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 yrs ago No communication

Frank Tipler Proof why there are no other

Pessimistic Views Optimist Curiosity is the by

everywhere: might give rise to intelligent life

to intelligent life Many planets detected in the

able to send signals for ~100 years It is not clear

g. the cold war) Fred Hoyle: The chance that higher

comparable to the chance that a tornado sweeping

learn we are not the center of the solar system, why

There are advanced civilizations They leave us alone

Cohen 1600 Feb 17, Rome " burned at stake for heresy

life exists on them Mathematician Gauss 1820 s

arrangement in Siberia " pythagorean theorem.

directive ) Rare Earth Hypothesis Astrophysical

rare, microbial life may be abundant The timescales

is roughly the same timescale that it takes for

and close planetary system encounters Project Ozma

Zoo Hypothesis How do we know Frank Tipler exists?

There are 4 billion people on this planet, surely an

$making his presence known to a sizeable fraction of$

7 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 Tipler Argument Pessimist 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 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 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. 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 ) 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 Von Neumann machines Early SETI Giordano Bruno The Zoo Hypothesis 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... They do not exist Pre-Copernican comparison The Zoo Hypothesis The Great Silence Pre-Copernican comparison 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

8 Unraveling the Mystery 1967 Galactic Radio Survey Mysterious repeated pulsed ratio signals Repeat every sec Pulse duration 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 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 /13 Pioneer 10 Solar System Gold disks with greetings, music First to leave Solar System Gold Plaque Arecibo Antenna Human Genome Scale of spacecraft & humans Solar system & Earth 3D pulsar map of location

SETI Search Space A Variety of Searches Date Observer

42 GHz % Eri, $ Tau 1968 Troitsky Gorky 21, 30 cm 12

42 GHz 10 nearby stars 1972 Troitsky Gorky 16, 30, 50 cm

stars 1972 Kardashev Europe Several All sky 1973- Dixon,

3 cm 70 nearby stars 1975-6 Drake, Sagan Arecibo 12.

nearby stars 1978 Horowitz Arecibo 21 cm 185 nearby stars

200 stars Begun in 1981 Targeted & All Sky 131,000

42 GHz META (1985) The NASA Search Sentinal continuation

109 channels The NASA Search Targeted Program 300-1000s

42 GHz, 1-3 GHz 770 Solar type stars Within 22 LY Good

34-m DSN dishes Scan entire sky (3-5 yrs) 107 channels,

talked him out of objections (Drake Eqn) Senate budget

Resolution Microwave Survey) In 1993 Budget of

Megachannel Extra-Terrestrial Assay 8x106 channels Very

LY BETA (1995) Fraction of Sky covered Sensitivity of

(1983) Each survey has been limited 1960 Richard Bryan -

9 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 Palmer, Zuckerman NRAO 21 cm 670 nearby stars 1972 Kardashev Europe Several All sky Dixon, Cole Ohio 21 cm All sky 1974 Bridle, Feldman Algonquin 1.3 cm 70 nearby stars 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 Planetary Society & SETI 131,000 channels 200 stars Begun in 1981 Targeted & All Sky 131,000 channels 1.42 GHz META (1985) The NASA Search Sentinal continuation of Suitcase SETI Billion-channel Extra-Terrestrial Assay 109 channels The NASA Search Targeted Program s 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) Fraction of Sky covered Sensitivity of Search Number of frequencies Suitcase SETI Horowitz (1983) 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

stars in Southern hemisphere 11000 hours; 240 light

'#$'% 3456&%7)%8-9%1:% ;)(67$2%67%<67%=>$$?

up Pioneer 10: signal beyond Solar System B5C&.(0*>.

)E% A(($''%I)>%7#$%G$E$>6&%'(.$E7.L(% ()115E.

signals: continuous or pulse More efficient,

. Should SKA International Institute of Space Law

Timelines ATA Allen Telescope Array ATA We Transmit?

Could we be the youngest technology in the galaxy?

term strategy We are culturally too immature Who

Organizations: U " nited Nations Committee on the

Galaxy SKA Square kilometer array collaboration

transmit a signal to all known stars, how many

time durations 10 years A signal could travel to

There are only 3 stars within 5 light years 40

10 Project Phoenix SETI Institute: Allen Telescope Array 1000 nearby sun-like stars from stars in Southern hemisphere hours; 240 light years "#$%"$&$'()*$% +,-%'./01%2.'#$'% 3456&%7)%8-9%1:% 1 3 GHz Realtime signal detection and follow up Pioneer 10: signal beyond Solar System B5C&.(0*>.D67$%*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 More efficient, narrower beam, bright No waterhole ; unique absorption lines? Several searches: Harvard, Berkeley, Lick.. Should SKA International Institute of Space Law International Academy of Astronautics Phoenix Timelines ATA Allen Telescope Array ATA 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 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 ~ 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

using the SETI@Home distributed computing platform The platform uses your unused CPU cycles to process radio telescope data With cheap

11 Timelines for Active SETI 1000 years: 1.7 million stars within 500 light years About 1 in every 100,000 stars in the Milky Way Citizen Science SETI efforts can be helped using the SETI@Home distributed computing platform The platform uses your unused CPU cycles to process radio telescope data With cheap multicore machines, there is a lot of underutilized computation time Currently has over 3 million users "#$%*>)C6C.&.7J%)I%'5(($''% %.'%2.M(5&7%7)%$'7.167$@%C57%.I%N$% E$D$>%'$6>(#%7#$%(#6E($%)I%'5(($''%.'% O$>)P% 0%=)(()E.%H%Q)>>.')E%

Young Solar-like Systems

Young Solar-like Systems FIG.2. Panels(a),(b),and(c)show 2.9,1.3,and 0.87 mm ALMA continuum images of other panels, as well as an inset with an enlarged view of the inner 300 mas centered on the (f) show