Existing laser technology could be fashioned into Earth's 'porch light' to attract alien astronomers

November 5, 2018 by Jennifer Chu, Massachusetts Institute of Technology
An MIT study proposes that laser technology on Earth could emit a beacon strong enough to attract attention from as far as 20,000 light years away. Credit: MIT News

If extraterrestrial intelligence exists somewhere in our galaxy, a new MIT study proposes that laser technology on Earth could, in principle, be fashioned into something of a planetary porch light—a beacon strong enough to attract attention from as far as 20,000 light years away.

The research, which author James Clark calls a "feasibility study," appears today in the Astrophysical Journal. The findings suggest that if a high-powered 1- to 2-megawatt were focused through a massive 30- to 45-meter and aimed out into space, the combination would produce a beam of infrared radiation strong enough to stand out from the sun's energy.

Such a signal could be detectable by alien astronomers performing a cursory survey of our section of the Milky Way—especially if those astronomers live in nearby systems, such as around Proxima Centauri, the nearest star to Earth, or TRAPPIST-1, a star about 40 light-years away that hosts seven exoplanets, three of which are potentially habitable. If the signal is spotted from either of these nearby systems, the study finds, the same megawatt laser could be used to send a brief message in the form of pulses similar to Morse code.

"If we were to successfully close a handshake and start to communicate, we could flash a message, at a data rate of about a few hundred bits per second, which would get there in just a few years," says Clark, a graduate student in MIT's Department of Aeronautics and Astronautics and author of the study.

The notion of such an alien-attracting beacon may seem far-fetched, but Clark says the feat can be realized with a combination of technologies that exist now and that could be developed in the near term.

"This would be a challenging project but not an impossible one," Clark says. "The kinds of lasers and telescopes that are being built today can produce a detectable signal, so that an astronomer could take one look at our star and immediately see something unusual about its spectrum. I don't know if intelligent creatures around the sun would be their first guess, but it would certainly attract further attention."

Standing up to the sun

Clark started looking into the possibility of a planetary beacon as part of a final project for 16.343 (Spacecraft, and Aircraft Sensors and Instrumentation), a course taught by Clark's advisor, Associate Professor Kerri Cahoy.

"I wanted to see if I could take the kinds of telescopes and lasers that we're building today, and make a detectable beacon out of them," Clark says.

He started with a simple conceptual design involving a large infrared laser and a telescope through which to further focus the laser's intensity. His aim was to produce an infrared signal that was at least 10 times greater than the sun's natural variation of infrared emissions. Such an intense signal, he reasoned, would be enough to stand out against the sun's own infrared signal, in any "cursory survey by an extraterrestrial intelligence."

He analyzed combinations of lasers and telescopes of various wattage and size, and found that a 2-megawatt laser, pointed through a 30-meter telescope, could produce a signal strong enough to be easily detectable by astronomers in Proxima Centauri b, a planet that orbits our closest star, 4 light-years away. Similarly, a 1-megawatt laser, directed through a 45-meter telescope, would generate a clear signal in any survey conducted by astronomers within the TRAPPIST-1 planetary system, about 40 light-years away. Either setup, he estimated, could produce a generally detectable signal from up to 20,000 light-years away.

Both scenarios would require laser and telescope technology that has either already been developed, or is within practical reach. For instance, Clark calculated that the required laser power of 1 to 2 megawatts is equivalent to that of the U.S. Air Force's Airborne Laser, a now-defunct megawatt laser that was meant to fly aboard a military jet for the purpose of shooting ballistic missiles out of the sky. He also found that while a 30-meter telescope considerably dwarfs any existing observatory on Earth today, there are plans to build such massive telescopes in the near future, including the 24-meter Giant Magellan Telescope and the 39-meter European Extremely Large Telescope, both of which are currently under construction in Chile.

Clark envisions that, like these massive observatories, a laser beacon should be built atop a mountain, to minimize the amount of atmosphere the laser would have to penetrate before beaming out into space.

He acknowledges that a megawatt laser would come with some safety issues. Such a beam would produce a flux density of about 800 watts of power per square meter, which is approaching that of the sun, which generates about 1,300 watts per square meter. While the beam wouldn't be visible, it could still damage people's vision if they were to look directly at it. The beam could also potentially scramble any cameras aboard spacecraft that happen to pass through it.

"If you wanted to build this thing on the far side of the moon where no one's living or orbiting much, then that could be a safer place for it," Clark says. "In general, this was a feasibility study. Whether or not this is a good idea, that's a discussion for future work."

Taking E.T.'s call

Having established that a planetary beacon is technically feasible, Clark then flipped the problem and looked at whether today's imaging techniques would be able to detect such an infrared beacon if it were produced by astronomers elsewhere in the galaxy. He found that, while a telescope 1 meter or larger would be capable of spotting such a beacon, it would have to point in the signal's exact direction to see it.

"It is vanishingly unlikely that a telescope survey would actually observe an extraterrestrial laser, unless we restrict our survey to the very nearest stars," Clark says.

He hopes the study will encourage the development of infrared imaging techniques, not only to spot any laser beacons that might be produced by alien astronomers, but also to identify gases in a distant planet's atmosphere that might be indications of life.

"With current survey methods and instruments, it is unlikely that we would actually be lucky enough to image a beacon flash, assuming that extraterrestrials exist and are making them," Clark says. "However, as the infrared spectra of exoplanets are studied for traces of gases that indicate the viability of life, and as full-sky surveys attain greater coverage and become more rapid, we can be more certain that, if E.T. is phoning, we will detect it."

Explore further: Supersharp images from new VLT adaptive optics

More information: Optical detection of lasers with near-term technology at interstellar distances, Astrophysical Journal (2018). DOI: 10.3847/1538-4357/aae380

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1.9 / 5 (9) Nov 05, 2018
Remember the 'interstellar asteroid Oumuamua'? It approached within .25 solar distance from the sun, AND .15 solar distance from the earth. It, on re-examination, showed internal trajectory control on approach to and away from the closest approach to the sun. It even accelerated on its way AWAT FROM the Sun, a clear indication it was a ship. As for a crew we cannot prove they are living or dead. Computers could handle it. Speculation is that it has sent back data to the species that made it. At least THIS alien species KNOWs that we are here. These may not have had warp drive, or if so know not ot use it in a solar system.

Do not forget the miners on Ceres.

THEY ARE COMING!! We have at the most 50 years. We are a backward, internally divided species on a small planet, and do not yet have real access to space or a serious unified space access program to make effective claim to our solar patrimony.

3.8 / 5 (5) Nov 05, 2018
Humans are very naive to think that technological progress means moral development. In other words, a civilization might reach the power to travel through space, but they may still be violent, cruel, exploitative. The universe is infinite, therefore infinite possibilities. There is no one good logical reason to expect goodness from aliens, as there is not a good logical reason to expect goodness from a person just passing by in front of my door.

To the best of my knowledge we are still missing a full 747, and record amount of money was spent trying to find it....
4.3 / 5 (3) Nov 05, 2018
This is not about aliens and their capabilities.

This is about life forms living on a planet that achieved sufficient awareness to recognize their own existence.

It is not important that aliens learn about us or us about them.

What is fundamental and crucial is that being able to leave a trace of our existence for a long time beyond our demise.

The way to do it is with solar sails embedded with physical and digital hieroglyphs and geometrical wave generating patterns. Sails floating at the edge of our solar system. Sails that can absorb photons from our sun and translate/propagate them in patterns, infinitely (photons do not age).

Shapes that can live on for billions of years beyond the existence of our solar system. For as far as we know, at this point in the history of the universe, no other life form within a reasonable distance have achieved awareness.

Lighting space with a laser is fruitless.
2.6 / 5 (5) Nov 05, 2018
OH_MY_GOD!! The lunatics have taken over the asylum! As the headline read, "The nut screws and bolts!"
Mark Thomas
3.9 / 5 (8) Nov 05, 2018
Earth's 'porch light' to attract alien astronomers

Dumb idea on multiple levels that is wasteful at best and risky at worst. If somebody was close they would already know about us. If they are 20,000 light years away, then what is the point? An answer and response that takes at least 40,000 years does not seem worth the risk of letting the Borg-equivalent know we are here and eager for assimilation. If FTL is possible, we will probably meet millennia before our stupid porch light message arrives. If aliens are already visiting (the recent U.S. Air Force video), we look dumb for ignoring what is right in front of us.
4 / 5 (4) Nov 05, 2018
what is the point?

Good point, since biological lifetimes are so much shorter, any interstellar travel for living biology is impractical. Except for our robots, nano-technology that can tell future Earth about things very far away, very far in the future. This doesn't require lasers telling them where we are.
Marvin Martian
3.8 / 5 (5) Nov 05, 2018
Radio stations have been around for about a hundred years. So there's already radio waves in a globe shaped volume with a diameter of 200 light years. If there are any space aliens in that volume they already have our radio waves to work with.
2.8 / 5 (6) Nov 05, 2018
One simply has to read the published accounts of 120 retired military officers with the highest security clearances who oversaw the operations of nuclear missile sites in Russia, England, and the U.S. They all reported a UFO hovering above the missile sites and disarmed the nuclear warheads by remote which then took weeks to rearm the warheads. Does that sound like a threatening gesture or were they sending a message to save us from ourselves?
2.3 / 5 (3) Nov 06, 2018
Oh Mark, Mark, Mark... I expect gibbering idiocy from all these other lunatics! But really, I did expect better of you. You must never leave your drink unintended around this gaggle of sheeple..

"There are Lies. There are Stupid Lies. And there are Drunken Stupid Lies!"

Guess which category I place BEMs, LGM, theosophist cargo-cult of flying saucers and hollow earth, EE/EU/Aether loons?
Mark Thomas
1 / 5 (2) Nov 06, 2018
rrwillsj, mislabeling is not an endearing trait. The analysis begins by considering the laws of physics, chemistry and planet formation that enable life to survive here appear to apply through the universe, thus conditions suitable for life are likely to be relatively plentiful. Without covering all the analysis, my personal guess is that bacteria are widespread and there is at least one other space-faring civilization between 4 light years and 4 billion light years from here. I have no hard proof of this, it is merely an educated guess, but I understand that many would agree. I also think it is unlikely that an advanced civilization has arisen nearby, but again, this is not yet clear. If you believe the entire universe if devoid of life outside of Earth, I believe that is one of the least likely outcomes, but I acknowledge that it could be correct. If you disagree with my thinking, try basing your arguments on science, not mislabeling.
3 / 5 (2) Nov 06, 2018
Please for the love of all things rational and logical read "The Three Body Problem" by Liu Cixin before you even consider that this might be a "good idea." If James Clark can't afford it I will buy him a copy. Questions of technical, physical or engineering are irrelevant to the risk analysis of what the maximum damage might be.
3.7 / 5 (3) Nov 07, 2018
With how many Nukes we have set off, and how many EMP's we have generated, that advanced civilizations know we are here is a forgone conclusion at this point if they are out there. (And as pointed out above by Marvin within 75 or so light years in all directions for the EMP timeline).
Da Schneib
5 / 5 (2) Nov 07, 2018
"Yoo hoo, aliens! Food here!"
Da Schneib
4.7 / 5 (3) Nov 07, 2018
Oh well, at least it'll fix global warming.

Remember the one about the aliens who show up with a book titled, "How To Serve Humankind?" It turns out to be a cookbook.
3 / 5 (2) Nov 07, 2018
Mark, What part of "Wanting and Wishing. Hoping and Praying?" is science?

Yes DS, truly food for thought! Though when you consider humanity's history as Homo Anthropophagus? Our appetite for reckless consumption of all life, intelligent or not.

I would bet any intelligent, technologically advanced alien are in full flight from this Galaxy. Before we can run them down.

"Bon Appetite!"
Mark Thomas
2.3 / 5 (3) Nov 07, 2018
The analysis begins by considering the laws of physics, chemistry and planet formation that enable life to survive here appear to apply through the universe, thus conditions suitable for life are likely to be relatively plentiful.

What part don't you get? No "Wanting and Wishing. Hoping and Praying" required.
5 / 5 (1) Nov 08, 2018
Quick build it right away, if they're an average of just 10k light years away we might get an answer back in 20 thousand years. Unless an asteroid has extincted Homo sapiens by then.

What it the signal is reached by alien space trolls and then thousands of years in the future a message is flashed across the Earth sky "ATT Earthlings...LOL at your stupid laser!"
Phyllis Harmonic
3 / 5 (2) Nov 08, 2018
Spectrographic analysis of our atmosphere would provide plenty of evidence of life to an outside observer (assuming life-chemistry is similar across the galaxy). No mega-lasers required.
5 / 5 (1) Nov 08, 2018
30 meter telescope

1 megawatt laser

There is no reason at all why an advanced civilization has to restrict itself to such tiny sizes and energies. If there are aliens out there, then they would have long ago catalogued every habitable planet in our local galaxy group. You cannot hide a life-bearing planet like Earth.

Whether they would want to contact us is another matter entirely.
Phyllis Harmonic
4 / 5 (4) Nov 08, 2018
"Yoo hoo, aliens! Food here!"

Reminds me of a Far Side cartoon. : )
1 / 5 (1) Nov 08, 2018
They should be stuffed and mounted as trophies for our future overlords.
Da Schneib
5 / 5 (2) Nov 08, 2018
"Yoo hoo, aliens! Food here!"

Reminds me of a Far Side cartoon. : )
Reminds me specifically of the deer with a target on it's chest with two others whispering, "My, what an unfortunate birthmark."

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