Alien hunters should search for artifacts on the moon, a study suggests |
The quest for these alien
artifacts could start with the
moon and other cosmic bodies near Earth, a new study finds.
The Drake Equation is used to estimate the number of civilizations in the Milky Way one can detect via their broadcast signals — or, more simply put, the odds of finding intelligent life in our galaxy. First proposed by radio astronomer Frank Drake in 1961, the equation calculates the number of communicating civilizations by analyzing several variables, such as the rate of formation of stars suitable for the development of intelligent life and the number of planets, per stellar system, with an environment suitable for life.
Currently, virtually all SETI (search
for extraterrestrial intelligence) experiments scan the skies looking for
radio or light signals. However, over the years, some researchers have
suggested that another, potentially better way to find evidence of alien life
is to not look for broadcasts from afar, but instead to hunt for what are
essentially messages in a bottle — a SETA (search
for extraterrestrial artifacts) approach.
For example, in 2004,
researchers suggested that broadcasting a signal across the cosmos is expensive
and inefficient. Instead, the scientists calculated that inscribing messages
onto a hunk of matter and launching it at potential extraterrestrial pen pals
would require about a
trillionth as much energy.
Another concern with conventional SETI is that extraterrestrial
civilizations may be long dead by the time astronomers do actually detect
signals from them. In contrast, extraterrestrial artifacts could provide a way for us to directly learn about alien civilizations, especially if these
artifacts are equipped with artificial intelligence, study author James
Benford, a physicist at Microwave Sciences in Lafayette, California, told
Space.com.
In the new study, Benford developed a version of the Drake equation
for artifacts. The new formula specifically focused on what he calls "lurkers"
— hidden and likely robotic extraterrestrial probes. Although the civilizations
that deployed these lurkers may well be dead, the lurkers themselves could
still be active enough to communicate with us.
A key difference between a SETA strategy and conventional SETI
approaches "is how it [SETA] involves actively looking for evidence
instead of passive observations," Benford said. "The SETI community
as a whole would need to think a new way."
When Benford compared his formula with the Drake equation, he
suggested the potential success rate of SETA was competitive with conventional
SETI. For example, if an alien civilization noted that artifacts were likely a
more cost-effective contact strategy than broadcasts, then SETA would prove
more successful than conventional SETI. However, if an alien civilization was
much like ours in that, it was only capable of spaceflight at interplanetary
speeds, then it might only ever build beacons instead of interstellar probes,
and conventional SETI would prove more successful than SETA.
Extraterrestrial civilizations that passed near the
sun might have been especially interested in launching probes at the
solar system, Benford said. He noted that about two stars come within one
light-year of the solar system per million years, and about one star comes
within 10 light-years every 5,000 years. The most recent close encounter the
solar system had was with Scholz's Star, which came within 0.82 light-years of
the sun about 70,000 years ago.
"On the 10,000-year timescale of agricultural civilizations on
Earth, about two stars have come within 10 light-years," Benford said.
Benford suggested first analyzing lunar images for signs of
extraterrestrial probes. He noted that NASA's Lunar Reconnaissance Orbiter has
taken about 2 million photos of the moon since 2009 "with resolution down
to about a foot (0.3 meters)," Benford said. "You can see Neil
Armstrong's footprints on the moon in some photos, but only a handful of these
images have been inspected by human eyes. We need to use AI [artificial
intelligence] software to look for structures, for signs of artificiality,
which could benefit sciences on Earth, such as archaeology."
Benford also suggested looking for alien artifacts located on other
bodies near Earth. These include Earth's Trojan objects (bodies located at
points in space where Earth and the sun's gravitational pull balance out) and
Earth's co-orbital objects (those sharing Earth's zone around the sun).
"China is planning a mission, ZhengHe, to one of these
co-orbital objects, 2016 HO 3, for launch in 2024," Benford said.
"It's going to come within 10 times Earth's distance to the moon."
Benford would not suggest looking on Earth itself. "If an artifact has been here a long time, it's been subject to the weather, damage, theft, or decay due to the elements," Benford said. "Over hundreds or thousands or millions of years, they're likely not really discoverable, whereas someplace like the moon — they could still be there."
All in all, "we can get a yes-no answer to part of the SETI
question by searching nearby Earth, and we can do it with experiments, not just
waiting for signals," Benford said. "SETI asks, 'Where are they?'
Well, maybe they're right next door."
Benford detailed his findings online on March
18 in the journal Astrobiology. He will also discuss his idea with Breakthrough
Listen, a $100 million, 10-year search for intelligent life in the universe
announced in 2015 by famed scientist Stephen Hawking and other researchers.
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