For the past 50 age , our efforts to detect extraterrestrial civilisation have largely focused on the hunting for tuner emissions . But this is hardly the only strategy at our disposal . Here are 14 intriguing ways we could prove that extraterrestrial really exist .
Top prototype : Christian Lorenz Scheurer .
If we ’re work to chance an extraterrestrial intelligence activity ( ETI ) , we ’re go away to realise their signatures . These signs can be organized into three introductory type : spectral signatures , physical artefact and structures , and remnants , or byproducts , of their technological activities . Some of these signatures could be deliberate attempts to get our tending , while others are simply leak .
Should we observe these signature , however , the challenge will in determining which are the workplace of an ETI and which are the product of some unknown or bizarre innate phenomena ( like the time we thought quasars were an alien beacon ) .
Here ’s what we should be await for :
1. Radio Signals
As remark , this is the most well - known of the SETI targets . tuner point emanating in narrow-minded , focussed bands could indicate the bearing of intelligent life .
We ’ve been leak electromagnetic waves of various vividness and frequency for well over a C , the remnant of goggle box program , roving telephone set conversation , satellite transmission system , along with military , civic and galactic radars . It ’s fair to assume that ETIs are doing the same affair ( peculiarly if intelligence agency converges around similar developmental trajectories ) . Radio signals could also be broadcast deliberately ( visit messages to alien , or METI),but that ’s high-risk .
Unfortunately , radiocommunication signals decrease in intensity level as they leak out into the cosmos . But bet on a sign ’s strength and frequence , these waves can broadcast for cosmologically vast distances and still post enough selective information to connote the bearing of levelheaded life . AstronomerJacob Haqq - Misrasays a transmitter beam power of 0.8 MW and a frequency of 2,380 MHz could be picked up by a “ watcher ” with a 1 km2 receiving antenna at distance of up to 200,000 calorie-free yr . That say , the receiver would have to focus on a specific spot for a really , really long time to pick up a meaningful signal .
2. Optical Signals
Aliens may also designedly transmit stilted infrared , seeable , or ultraviolet emission .
For example , noncitizen could utilize hefty lasers to communicate across stellar distances at various optic wavelength . laser are particularly effective for point - to - point communication , so we can conceptualise of automated system that point lasers at candidate systems . optical maser have tight beam which can run wads of data . Moreover , unlike seeable light ( which can be blank out by dust in the galaxy ) , light in the infrared spectrum can easily riddle our galax ’s moth-eaten sensitive .
To date , Berkeley ’s SETI program has scanned about 20,000 object ( mostly Sunday - like stars ) at 10 - moment intervals , so if the optical maser blinking frequency is longer than that , we ’re out of luck . The Berkeley researcher are looking for pulse bright flashing sign or continuous signals . Nothing interesting has been discovered so far .
3. Microwave Signatures
The modern search for aliens formally began in 1959 with the publication of a newspaper publisher by Philip Morrison and Giuseppe Cocconi . Their article , “ look for for Interstellar Communications , ” proposed a lookup of nearby sunshine - similar stars for measured microwave oven wireless sign on the 21 - centimeter H argumentation .
4. Artificially Appearing X-Ray and Gamma Ray Bursts
ETI ’s could also get our attention through the deliberate transmitting of high - energy go - ray and da Gamma ray bursts .
But this would require hideous sum of vim per minute — something that only a first-rate - potent civilization would be adequate to of . According to John A. Ball , an advanced ETI should be up to of transmitting a two - millisecond pulsing encoding 1×1018 bits of information . That ’s “ like to the estimated total entropy content of Earth ’s biosystem — genes and meme and including all libraries and computer media . ”
5. Neutrino Communication
Image : IceCube Collaboration .
High - energyneutrinoscould also beused as a communicating medium . They ’re particles with no billing but with a discernible energy and whirl . These ghostly particles have no residual great deal and can travel cosmogonic length at the stop number of light . With this in head , some scientists say we should start sniffing neutrinos for traces of message ( once we have the engineering science , of course — and we ’re getting there ) . Specifically , we should be on the look - out for strange or concentrated neutrino emissions . As J. G. Learned and S. Pakvasa havenoted , “ Such signals from an innovative civilization , should they survive , will be eminently detectable in existing neutrino detectors . ”
6. Gravitational Waves
Image : NASA .
Similarly , an ETI could broadcast gravitational waves our way . They could do this by shaking a planet or something else with extreme mass in manner that could produce an obvious signal . One of the advantages of gravitational wave is that they jaunt at the speed of illumination . But it may be some time before we have asensitive enough undulation detector . That said , this seems like a rather heavy and energy - intensive way to post a sign .
7. Industrial Waste Signatures
figure : Suicup via Wikimedia Commons .
Spectrographic analysis ofexoplanetary atmospherescould indicate the presence of elevated level of carbon copy dioxide ( and other industrial bi - mathematical product ) beyond what ’s naturally potential . The challenge for us will be in figure out which factor , and in which ratios , these gasolene can appear exclusively as the result of an sound civilisation at work .
8. Calling Cards
French astronomer Luc Arnold say we should be on the hunt for deliberately placed artificial objects .
Using the transit method of detection , we could feel oddly shaped aim revolve around adept — like a absolutely triangular construction or a two - sieve target ( conceive of a rectangle with a boxful - like kettle of fish cut in the middle ) . These so - calledcalling cardswould alert us to the presence of an ETI — though this scheme will only form for those systems whose orbital planer aligns with our line of products of sight .
“ A singular lightcurve would be created by liberal - aeronaut transiting their star successively in a distinct personal manner , ” writes Arnold . “ At each period , we would observe a series of transits whose numeral and timing would take its artificial nature and will of communicating . ”
9. Dyson Spheres
Image : Dyson Sphere by Eburacum45 .
We should also look forDyson Spheres — those hypothetical megastructures approximately the size of a planetary orbit and lie of a monumental raiment of sun - enveloping solar collector . These shells would steep near all of a master of ceremonies star ’s solar output , so they ’d be practically invisible , except that they would still give off heat . accordingly , we should scan the heavens for blackbody objects radiating in the far infrared around 10 micron in wavelength .
We should also look for signs of Dyson Spheres in neighboring galaxies , what would seem aslarge empty swaths of space . This could indicate the ranch of a civilization approachingKardashev IIIstatus .
10. Exoplanets That Appear Out of the Ordinary
There are also supramundane planets to reckon , an idea conceptualize by Paul Birch .
picture : Steve Bowers .
These are planets that have been totally reworked by an advanced civilisation and would admit Earth - like planetary planets or gas pedal goliath .
For example , an ETI could make a new surface above a Jupiter - comparable major planet at hundreds of thousands of kilometre from its centre of mass , where the gravity is more like an earthly concern - same major planet . This surface would be suspended using so - called Mass Stream Technology . Orion ’s Armexplains :
Mass Stream Technology use aggregative particle beams which encircle the major planet or star to support complex body part above it ; by exerting thrusting magnetically against these beams ( known as dynamical orbital halo ) , suborbital structure can be suspended at any acme . dynamical contraction penis and dynamic orbital rings using mass stream technology would be configure into a framework around the planet which would support platforms , which could in good turn support a large biosphere . item-by-item platform could then be extended into band which could afterwards be extend into a complete eggshell .
speak of orbital anchor ring , we should look for those , too — another idea proposed by Birch . These are supposititious rings in low planetary compass that go around above orbital speed and have mend tethers descend down to the surface .
Detecting supramundane planet place a challenge , but inexplicable spectrographic atmospherical signatures would be a proficient billet to start .
Another matter to front out for are liberal - floatingSteppenwolf Planets . Dorian Abbot and Eric Switzer contend that a rogue satellite ( one ejected from its planetary system ) could still foster a smooth sea under ice as a upshot of geothermal flux . Such a satellite could be detected from solar radiation , while its thermal emissions could be pinpoint in the far infrared if it transcend within 1,000 AU of Earth .
11. Artificial Illumination
Less speculatively , we could plainly appear for artificial lighting on exoplanets ( or megastructures , for that matter ) .
We may finally develop telescopic engineering on the ground and in place , likea star shade , that candetect phase modulation bring forth by very strong artificial illumination on the nightside of satellite as they orbit their parent stars . Like the lookup for radio signature , this would admit for the detection of civilization roughly equal to our own in terms of technical edification .
12. Transiting Space Habitats
If aspace habitatis declamatory enough , like a Tsiolkovsky or O’Neill habitat , it could be spotted using the transit method acting ( i.e. , find the slight and temporary dimming of a distant adept ) . Other home ground that could be expectant enough includeRing Worlds , Halos , andBishop Rings , though it would have to be a rather monolithic spread out cycle space place ) .
13. Spacecraft
We shouldalso look for starships . Back in 1986 , Michael Harris made the slip that advancedETIs may use antimatter as an efficient fuel sourceto power interstellar ballistic capsule . We could detect these engines via gamma beam emission . The challenge will be in recognize these antimatter - combust vehicle for what they are , perhaps by chase after and measuring their motions through space . According to Robert Zubrin , the fumes from an antimatter locomotive engine could be detected from as far as 300 light class from Earth — an area of space contain well over 100,000 genius .
figure : IKAROS .
Other possibilities include Gregory Benford ’s idea thatsynchrotron radiation in the bow blow of a magnetically sieve starship would be detectable at microwave and wireless frequencies , or the detection of a decelerating magnetised sheet — a process that would also produce a bowing shock . allot to Zubrin , this would heat the interstellar culture medium to a degree dependant on the ship ’s velocity , creating a plasm that would encounter the charismatic field of the magsail and bring about radiation .
14. Probes
Self - reduplicate spacecraft , orprobes , are another decided possible action . Signs of an ETI could survive in our very own solar system — we just have to figure out where to expect . For example , a Bracewell communication probe could be idle nearby , waiting for us to traverse some kind of technical threshold .
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