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

Nov. 4, 2018 – If extraterrestrial intelligence exists somewhere in our galaxy, a new MIT study proposed 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
Newspaper. The findings suggest that a high-powered 1- to
2-megawatt laser were focused through a massive 30- to 45-meter
telescope and desire out into space, the combination would produce
a beam of infrared radiation strong enough to stand out from the
sun's energy.

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Such a signal could be detectable by
alien astronomers performing a cursory survey of our section of
the Milky Way – especially if these astronomers live in nearby
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 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 Morse code.

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

The concept 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
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 a look at our star
immediately see something unusual about its spectrum. I do not 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
16.343 (Spacecraft and Aircraft Sensors and Instrumentation),
Course taught by Clark's Advisor, Associate Professor Kerri Cahoy.

"I wanted to see if I could take the
Types 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
sun's own infrared signal, in any "cursory survey by an
extraterrestrial intelligence. "

He Founded combinations of lasers and
telescopes of various wattage and size
2-megawatt laser, pointed through a 30-meter telescope, could
produce a signal strong enough to be detectable by
astronomers in Proxima Centauri, 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
in any survey conducted by astronomers within the
TRAPPIST-1 planetary system, about 40 light-years away. Either
setup, he estimated, could produce a detectable signal
from up to 20,000 light-years away.

Both scenarios would require laser and
telescope technology that has 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
Chile.

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

He acknowledges that a laser megawatt
would come with some safety issues. Such a beam would produce
flux of 800 watt of power per square meter, which
is approaching that of the sun, which includes about 1,300 watts
per square meter. While the beam would not be visible, it could
still damage people's vision if they were to look directly at it.
The beam could also be 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 one's living or orbiting much,
then that could be 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 possible, Clark then flipped the problem
At present today, it should be able to
detect such an infrared beacon if it was produced by astronomers
elsewhere in the galaxy. He found that, while a telescope 1 meter
or larger would be able to 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
laser beacons that could 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
viability of life, and as full-sky surveys
and become more rapid, we can be sure that, if E.T. is
phoning, we will detect it. "

PAPER: Optical Detection of Lasers
with Near-term Technology at Interstellar Distances:
http://iopscience.iop.org/article/10.3847/1538-4357/aae380