Planets & LifePlanets & LifePHYS 214PHYS 214

Dr Rob ThackerDr Rob ThackerDept of Physics (308A)Dept of Physics (308A)

thacker@astro.queensu.cathacker@astro.queensu.caPlease start all class related emails Please start all class related emails

with “214:”with “214:”

Today’s LectureToday’s Lecture SETI SETI

how and where to lookhow and where to look What to look forWhat to look for

“An absence of evidence is not evidence of absence” Sir Martin Rees

Credit: From presentation by Dan WerthimerDan Werthimer

Early (1800s) SETI ideas focused onour sending (visible) messages ratherthan detecting “them”.

Ideas focused on creating largeregions on Earth that could beseen from outerspace:

Example: Gauss’s (1820) idea to set up enormous fields (trees orwheat for example) that were geometrically aligned .

Of course we nowadays we broadcastour existence much more readily.

Where & what should we Where & what should we look for?look for?

Which frequencies? Which frequencies? Radio Radio

Leaked or intentional messages?Leaked or intentional messages?OpticalOptical

Powerful lasers can outshine stars in small Powerful lasers can outshine stars in small wavebandswavebands

The “next big discovery”…The “next big discovery”…

Direction? Direction? Targeted search?Targeted search?All-Sky survey?All-Sky survey?

Atmospheric EM spectrum Atmospheric EM spectrum transmissiontransmission

Sensible places to look

Categories of signalsCategories of signals We can look for 3 different types of signalsWe can look for 3 different types of signals

1)1) Leakage signals associated with local Leakage signals associated with local communication on a planet (10communication on a planet (1066 W) W)

2)2) Signals used to communicate of world perhaps Signals used to communicate of world perhaps to another colony or space craft (10to another colony or space craft (1088 W*) W*)

3)3) Intentional beacons designed to be “heard” Intentional beacons designed to be “heard” (10(101212 W*?) W*?)

It seems unlikely to us 3 will occur, but at It seems unlikely to us 3 will occur, but at present our detection limits force us to present our detection limits force us to look for these kinds of signalslook for these kinds of signals

*These are equivalent isotropic powers, the signal would actually be beamed in a small angle

From previous lecture: From previous lecture: Comparison of some SETI Comparison of some SETI

searchessearchesSurveySurvey # of stars# of stars Detection Detection threshold/ threshold/

W mW m-2-2

EIRP at 4 EIRP at 4 ly / Wly / W

EIRP at EIRP at 1000 ly / W1000 ly / W

AreciboArecibo 280280 881010-27-27 101088 9910101212

Allen Allen Telescope Telescope (SETI (SETI Inst., Inst., 2010?)2010?)

100000100000 ~1~11010-25-25 22101099 10101414

SKA SKA (2016?)(2016?)

100000100000 881010-29-29 101066 9910101010

EIRP=Equivalent isotropic radio power, corresponds to the strength of the transmitterOnly the SKA could detect a 106 W antenna at 1 ly away (it could at 4 ly actually)

Frequencies, bandwidth & Frequencies, bandwidth & channelschannels

Amplitude modulation (AM) radio Amplitude modulation (AM) radio works by modulating the amplitude works by modulating the amplitude of the carrier wave & a “side band”of the carrier wave & a “side band”

Frequency modulation (FM) radio Frequency modulation (FM) radio works by modifying the frequency works by modifying the frequency of the carrier waveof the carrier wave

Both of these methods require Both of these methods require more frequencies around the more frequencies around the central frequency to carry central frequency to carry informationinformation The total amount of frequency The total amount of frequency

range required is the range required is the bandwidthbandwidth A A channelchannel is a region of frequency is a region of frequency

space centered on the central space centered on the central carrier, thus allowing the signal carrier, thus allowing the signal riding on the carrier wave to be riding on the carrier wave to be detecteddetected So if you want to detect signals you So if you want to detect signals you

need as many channels as possibleneed as many channels as possible

Typical terrestrial radio Typical terrestrial radio frequenciesfrequencies

Band nameBand name AbbrAbbr ITU ITU bandband

Frequency & Frequency & WavelengthWavelength

UsesUses

Low freq.Low freq. LFLF 55 30-300 kHz, 10km-1km30-300 kHz, 10km-1km Longwave Longwave broadcastingbroadcasting

Medium freq.Medium freq. MFMF 66 300-3000 kHz, 1km-100m300-3000 kHz, 1km-100m AM radioAM radioHigh freq.High freq. HFHF 77 3-30 MHz, 100m-10m3-30 MHz, 100m-10m Amateur Amateur

radioradioVery high Very high freq.freq.

VHFVHF 88 30-300 MHz, 10m-1m30-300 MHz, 10m-1m FM radio, FM radio, some TVsome TV

Ultra high Ultra high freq.freq.

UHFUHF 99 300-3000 MHz, 1m-300-3000 MHz, 1m-100mm100mm

TV, TV, microwave microwave ovens, mobile ovens, mobile phonesphones

Super highSuper highfreq.freq.

SHFSHF 1010 3-30 GHz, 100mm-10mm3-30 GHz, 100mm-10mm Microwave Microwave devices, devices, wireless LANwireless LAN

Extremely Extremely high freq.high freq.

EHFEHF 1111 30-300 GHz, 10mm -1mm30-300 GHz, 10mm -1mm Radio Radio astronomyastronomyITU=International Telecommunications Union

Conflict of radio astronomy Conflict of radio astronomy with new communication with new communication

technologiestechnologies As technology improves terrestrial wavebands As technology improves terrestrial wavebands

are increasing in frequency and also are increasing in frequency and also bandwidthbandwidth

The International Telecommunications Union is The International Telecommunications Union is responsible for allocating different frequency responsible for allocating different frequency bands to different technologiesbands to different technologies

Thus far, wavebands associated with important Thus far, wavebands associated with important molecules (such as H, NHmolecules (such as H, NH33) have been ) have been protectedprotected

However, in the future it is unclear whether However, in the future it is unclear whether increasing economic pressure to assign increasing economic pressure to assign bandwidth will eventually make high sensitivity bandwidth will eventually make high sensitivity radio astronomy virtually impossibleradio astronomy virtually impossible

What about the interstellar What about the interstellar medium?medium?

Optical signals can be easily Optical signals can be easily obscured by clouds of dustobscured by clouds of dust

Radio can travel through the Radio can travel through the dust easily thoughdust easily though

However, at lower frequencies However, at lower frequencies (below 1 GHz) background (below 1 GHz) background noise from the galaxy becomes noise from the galaxy becomes a problema problem Easier to see a narrow band Easier to see a narrow band

signal above the noise than a signal above the noise than a wideband onewideband one

Signal will also spread out due Signal will also spread out due to Doppler shift & interaction to Doppler shift & interaction with interstellar mediumwith interstellar medium

What kind of message What kind of message should we look for?should we look for?

The signal should be immediately differentiable The signal should be immediately differentiable from any natural sourcesfrom any natural sources Most natural signals tend to be irregular and widely Most natural signals tend to be irregular and widely

spaced in frequency (but not always! There is one very spaced in frequency (but not always! There is one very famous example) famous example)

We can appeal to mathematical relationships for We can appeal to mathematical relationships for example:example: Prime numbers: 1,2,3,5,7,11,13,17,19,..Prime numbers: 1,2,3,5,7,11,13,17,19,.. Mathematical constants, Mathematical constants, ,e for example,e for example Space signals in frequency space? (Sagan)Space signals in frequency space? (Sagan)

What about encoding pictures? If we send a What about encoding pictures? If we send a signal that has a length that is a product of 2 signal that has a length that is a product of 2 prime numbers that could be interpreted as prime numbers that could be interpreted as describing a 2d map describing a 2d map

11111100001000011110000010000111110 With 35 bits it can be arranged as 5x7 or 7x5

While we recognize the first one, who’s to say that the second version isn’t used by a civilization somewhere?

However given a long enough message a natural ordering may well be apparent

Consider the following Consider the following binary messagebinary message

Describe the numeric system from 1 to 10 in binary

Atomic numbers 1, 6,7,8,15 (H,C,N,O,P)

Formulas for sugars and bases in nucleotides of DNA

Double helix of DNA

Number of nucleotides in human DNA

Human

Height of human in unit’s of signal’s wavelength (12.6 cm)

Human population

Pluto, Neptune, Uranus, Saturn, Jupiter, Mars, Earth (offset), Venus, Mercury, SUN

Arecibo dish

Diameter of Arecibo dish

The Arecibo Message

2d map is encoded into binary and sent, 1679 bits=23*73

The LGM-1 eventThe LGM-1 event Graduate student Jocelyn Bell Graduate student Jocelyn Bell

was responsible for searching was responsible for searching through miles of graphical through miles of graphical output from the new Cambridge output from the new Cambridge radio telescoperadio telescope

She found a pulse with a 1.337 She found a pulse with a 1.337 second periodsecond period First assumed to be noise due to First assumed to be noise due to

its regularityits regularity After that, the discoverers half-After that, the discoverers half-

seriously proposed, as an seriously proposed, as an alternative explanation, that the alternative explanation, that the signal might be a beacon or a signal might be a beacon or a communication from an communication from an intelligent extraterrestrial intelligent extraterrestrial civilization and named it civilization and named it LGM-1LGM-1 LGM=“little green men”LGM=“little green men”

Later realized to be caused by a Later realized to be caused by a rotating neutron star rotating neutron star

Optical SETIOptical SETI In 1961 Charles Townes pointed In 1961 Charles Townes pointed

out that sending pulses of laser out that sending pulses of laser light could be a potential light could be a potential mechanism for broadcasting a mechanism for broadcasting a civilizations existencecivilizations existence

The light must be distinguishable The light must be distinguishable from the star, but a directed laser from the star, but a directed laser can be much brighter than a star in can be much brighter than a star in a narrow wavebanda narrow waveband

It is easy for planets to overwhelm It is easy for planets to overwhelm their suns in radio waves, but not their suns in radio waves, but not visible visible

Jupiter is the strongest radio source Jupiter is the strongest radio source in the skyin the sky

Powerful lasers have a very well Powerful lasers have a very well defined wavelengthdefined wavelength

Results? Reines and Marcy in 2002 Results? Reines and Marcy in 2002 searched 577 nearby stars with searched 577 nearby stars with sensitivity to detect >60 kW lasers sensitivity to detect >60 kW lasers focused from a 10m telescopefocused from a 10m telescope

Nothing was detectedNothing was detected

For a recent report on Optical SETI see: http://www.spectrum.ieee.org/nov06/4710

Optical SETI at the Lick Observatory

The Water HoleThe Water Hole

Can’t get awayfrom noise inthe detector

Emission fromour own atmosphere

Noise associatedwith thegalaxy

Any technical society with radio astronomy will know this.

Radio telescope field of Radio telescope field of viewview

Sensitivity of a telescope is Sensitivity of a telescope is proportional to the area proportional to the area times the channel bandwidth times the channel bandwidth times time of pointingtimes time of pointing SSDD22√√tt Dictates large DDictates large D

However, we do not know However, we do not know where the source comes where the source comes fromfrom Dictates a large field of viewDictates a large field of view

Field of view is given by Field of view is given by D – argues for smaller D – argues for smaller telescopestelescopes

For a large dish, the number For a large dish, the number of pointings you need to of pointings you need to make increases as the make increases as the square of the diametersquare of the diameter

1

2=21D/2

D

Famous SETI projectsFamous SETI projects OZMA (Frank Drake) -

The first modern radio search (at Green Bank) 200 hours of observing 200 hours of observing

two nearby starstwo nearby stars Ohio SETI program

Used the “Big Ear” telescope, detected the infamous “Wow!” signal

META (1985, Paul Horowitz) – 8.4 million channels monitored Partly funded by Steven

Spielberg

Project PhoenixProject Phoenix Following the cancellation of Following the cancellation of

the NASA SETI program, the NASA SETI program, this project has been funded this project has been funded entirely by private sourcesentirely by private sources

Ran from 1995-98 on radio Ran from 1995-98 on radio telescopes in Australia & telescopes in Australia & USA (Parkes, Green Bank & USA (Parkes, Green Bank & Arecibo) Arecibo) Looked at both southern & Looked at both southern &

northern hemisphere starsnorthern hemisphere stars 800 sun-like stars within 800 sun-like stars within

200 ly, at frequencies of 1-3 200 ly, at frequencies of 1-3 GHz, 1Hz at a time.GHz, 1Hz at a time.

The search is for narrow-The search is for narrow-band “artificial” signalsband “artificial” signals

(Radio) SETI search (Radio) SETI search spacespace

~End of “waterhole”

This is what matters

SETI@home: Lots of data to SETI@home: Lots of data to processprocess

Scientifically, the computing methods involved in SETI@home have proven very productive.

SETI fundingSETI funding SETI is a truly unusual endeavour inspiring passions on SETI is a truly unusual endeavour inspiring passions on

both sidesboth sides Cynics, with strong arguments, dismiss it as a utter waste of timeCynics, with strong arguments, dismiss it as a utter waste of time Proponents, with strong arguments, believe it to be of Proponents, with strong arguments, believe it to be of

monumental significancemonumental significance As of 2007, SETI is currently not funded by any As of 2007, SETI is currently not funded by any

government agencies anywheregovernment agencies anywhere In the US, SETI funding was stopped in 1994In the US, SETI funding was stopped in 1994 However, strong public interest continues to provide private However, strong public interest continues to provide private

fundingfunding The continuing growth of interest in astrobiology at both The continuing growth of interest in astrobiology at both

public and political levels, seems to indicate that SETI public and political levels, seems to indicate that SETI probably will receive public funds again in the futureprobably will receive public funds again in the future However, I’d like to get results from TPF/Darwin for pHowever, I’d like to get results from TPF/Darwin for pll before we before we

start doing that – if we don’t find planets with atmospheres start doing that – if we don’t find planets with atmospheres indicating life, then SETI is a complete waste of time in IMHOindicating life, then SETI is a complete waste of time in IMHO

You are free to draw your own conclusions – the stakes are You are free to draw your own conclusions – the stakes are clearly significantclearly significant

Allen Telescope ArrayAllen Telescope Array UC Berkeley, SETI Institute UC Berkeley, SETI Institute

collaborationcollaboration 13.5 million donated by Paul 13.5 million donated by Paul

Allen (Microsoft cofounder)Allen (Microsoft cofounder) 350 6.1m antennas, about 350 6.1m antennas, about

1/71/7thth area of Arecibo area of Arecibo TO be completed 2008-9?TO be completed 2008-9?

Many small dishes, so large Many small dishes, so large field of viewfield of view

100% devoted to SETI 100% devoted to SETI researchresearch

Should cover at least Should cover at least 100,000 stars and possibly 100,000 stars and possibly up to 1 millionup to 1 million

Proving to be a scientifically Proving to be a scientifically useful proving ground for useful proving ground for technology that could be technology that could be adapted to the SKAadapted to the SKA

Array elements in snow!

SETI Contact protocolSETI Contact protocol1) Is it really extraterrestrial?1) Is it really extraterrestrial?2) Get confirmation from other astronomers. 2) Get confirmation from other astronomers.

(If extraterrestrial, tell your government about it). (If extraterrestrial, tell your government about it). 3) If convincing: announce to International Astronomical 3) If convincing: announce to International Astronomical

Union, Secretary General of the UN, inform SETI Union, Secretary General of the UN, inform SETI groups. groups.

4) Make the first public announcement 4) Make the first public announcement 5) Make data available to all. 5) Make data available to all. 6) Everyone carefully record & disseminate signals6) Everyone carefully record & disseminate signals7) Protect frequencies. 7) Protect frequencies. 8) Don't broadcast back to the ETs! Requires Debate.8) Don't broadcast back to the ETs! Requires Debate.9) Study signals. The SETI Committee of the International 9) Study signals. The SETI Committee of the International

Academy of Astronautics keeps a list of experts to call Academy of Astronautics keeps a list of experts to call on.on.

What about UFOs and all What about UFOs and all that?that?

(Ahem!) No credible evidence(Ahem!) No credible evidence ““Oh, the government and scientists Oh, the government and scientists

are just covering it all up!”are just covering it all up!” Scientists are extremely competitive Scientists are extremely competitive

people, trust me, if someone had people, trust me, if someone had found something worth knowing found something worth knowing about they’d let people knowabout they’d let people know

UFO sightings tell us nothing more UFO sightings tell us nothing more than every now and again there are than every now and again there are things in the sky we can’t explainthings in the sky we can’t explain

What about crop circles, What about crop circles, abductions etc?abductions etc? Would you travel a hundred trillion Would you travel a hundred trillion

miles to mow down some wheat?miles to mow down some wheat? Sleep paralysis, false memoriesSleep paralysis, false memories

They’re here already and they They’re here already and they don’t want us to knowdon’t want us to know Impossible to argue against, but do Impossible to argue against, but do

you really believe that?you really believe that?

Summary of lecture 30Summary of lecture 30 Both radio and optical searches for SETI are Both radio and optical searches for SETI are

possiblepossible The main problems areThe main problems are

Large frequency space to searchLarge frequency space to search Low signal power requires high sensitivityLow signal power requires high sensitivity

Searching over large areas of sky presents Searching over large areas of sky presents unique problemsunique problems High sensitivity requires a big dish, which High sensitivity requires a big dish, which

enforces a small field of viewenforces a small field of view Must point separately at different areas of skyMust point separately at different areas of sky

SETI is currently not funded by government SETI is currently not funded by government grants, but now has its own dedicated facility grants, but now has its own dedicated facility – the ATA– the ATA

Final lectureFinal lecture Future technology ideasFuture technology ideas

Comments on the finalComments on the final