For about
a week in 1960, radio astronomer Frank Drake thought he might have discovered

He had
pointed the National Radio Astronomy Observatory’s new 26-meter telescope at
the star Epsilon Eridani on April 8 of that year, and within minutes, the
instruments went wild. The telescope’s readout device, a chart recorder that
used a pen to scratch out signatures of incoming signals on paper, scribbled
erratically. A speaker connected to the telescope blared a train of strong pulses
— just the kind of transmission expected from an intelligent sender. Drake was
stunned. Could finding E.T. really be this easy?

wasn’t. When the telescope found the signal again several days later, a radio
antenna pointed in different direction also picked up the noise. The signal
wasn’t otherworldly at all; it was coming from an earthly source, like an

never picked up any interstellar broadcasts during his two months observing Epsilon Eridani and another
sunlike star, Tau Ceti, with the radio telescope in West Virginia (SN:
). But that first foray into the search for extraterrestrial
intelligence, or SETI, sparked a growing field of efforts to scout out fellow
intelligent creatures among the stars. And now, with recent discoveries in
astronomy, new technologies and a flush of new money, SETI is in renaissance.

National Radio Astronomy Observatory in 1960
In April 1960, radio astronomer Frank Drake used a 26-meter telescope at the National Radio Astronomy Observatory in West Virginia (pictured) to observe two nearby, sunlike stars for alien radio broadcasts. The observing campaign, which he dubbed Project Ozma, was the world’s first modern search for extraterrestrial intelligence.NSF, AUI, NRAO

really difficult to overstate how much the field has been transformed” in the
last few years, says Andrew Siemion, director of the University of California,
Berkeley’s SETI Research Center.

and better telescopes are probing deeper into the night sky. Sophisticated
computational tools are poring over massive datasets on increasing numbers of
stars and at a wider variety of frequencies. Observatories around the world are
performing regular observations as part of Breakthrough Listen — a $100 million
effort funded by Russian billionaires Yuri and Julia Milner to conduct the most comprehensive search for
extraterrestrials yet

(SN: 7/20/15).

So far, SETI
scientists have found nothing but radio silence. Still, they are undeterred. They’ve
scoured only a tiny fraction of the places E.T. could be (SN:
). And SETI’s collective observing power will make scientists 1,000
times more likely to find E.T. during this decade than they were in the 2010s, Siemion

This is,
he says, “a boom time for SETI.”

Eyes on the sky

decades, the hunt for intelligent aliens languished on the fringes of the scientific establishment (SN:
), viewed by many researchers as a “strange, boutiquey sort of thing
that’s not really astronomy,” says Siemion, principal investigator for
Breakthrough Listen. Short-lived U.S. federal funding for the field abruptly
ended in 1993, after which “SETI went underground and became very insular.”

SETI’s profile is changing, as our understanding of the universe evolves. Back when
Drake was making his observations, we hadn’t yet laid eyes on a planet around
another star. Within just the last decade, we’ve discovered thousands of exoplanets, giving new credence to arguments
that life beyond Earth is entirely possible (SN: 10/4/19).

In February,
Breakthrough Listen released the largest ever stockpile of SETI observations
for members of the astronomical community to analyze. The dataset, collected by
the Parkes radio telescope in Australia, the Green Bank Telescope in West
Virginia and the Automated Planet Finder in California, included a survey of radio
emissions from the disk of the Milky Way and the region around its core
supermassive black hole.

Green Bank Telescope
The behemoth 100-meter Green Bank Telescope in West Virginia is one of several observatories around the globe now contributing observations to Breakthrough Listen, the most comprehensive search for extraterrestrial life yet.GBO, AUI, and NSF (CC BY 3.0)

finding very advanced civilizations, I think galactic center very exciting,”
Siemion says. There, he speculates that some super tech-savvy aliens could have
built an extremely powerful radio transmitter charged by the Milky Way’s
supermassive black hole.

To find alien
civilizations working with more modest radio equipment comparable to our own,
searchers look to nearby stars. That was the approach that Sofia Sheikh, an
astronomer at Penn State, took in analyzing Breakthrough Listen observations of
20 of the sun’s stellar neighbors. All of those stars are in positions relative
to Earth that would allow any aliens around those stars to see Earth orbiting in
front of the sun — the same way that telescopes like TESS spot
). Those aliens might therefore be able detect Earth’s presence and target
our planet with a message.

and colleagues came up empty in their search. “Reporting null
results isn’t fun,” she says of her analysis, which was posted at on
February 14 and submitted to the Astrophysical Journal. But it does tell
other astronomers “this particular space has already been searched, go search
somewhere else,” she says. Given the vast cosmic real estate where E.T. might
be, checking out every little stellar neighborhood helps.

observatories joining the Breakthrough Listen cohort will start looking in a
lot of other places in the next few years. The MeerKAT array in South Africa is
gearing up to survey 1 million nearby stars. The Very Large Array in New
Mexico, seen in the 1997 film Contact, is getting its first SETI
instrument and will start looking for aliens in the background of its
observations for other astronomy studies in 2021.

Building better filters

more eyes on the sky is a key part of SETI. But while telescopes are heaping up
a massive haystack of data, there’s still the task of searching for any needles
buried within. And it could take picking through the same data more than once. New
computer algorithms can always revisit old observations to search for blips
that previous analyses missed.

Often in
radio astronomy, “the most interesting discoveries are not made on the first or
the second or even the third analysis of the dataset,” Siemion says. For
example, brief, brilliant flashes of radio waves from distant galaxies called fast
radio bursts were first discovered in a reexamination of
old data from the Parkes telescope

(SN: 7/25/14).

the perennial challenge is devising techniques to better distinguish potential alien
signals from radio interference by earthly technology. SETI scientists are
usually seeking the same kind of tight, well-defined radio transmissions that
human electronics produce. Such signals are easily distinguishable from radio
waves emanating from natural sources, such as stars or galaxies, which tend to
vary slowly over time or be smeared out across many frequencies. But that means
scientists have to judge whether any promising signals they detect are coming
from deep space or from a nearby a cell phone or satellite.

One way
of doing this is to point a telescope at a target, like a star, then somewhere
else. Any radio signals that appear when the telescope is pointed in both
directions are probably humanmade radio interference. Conventional computer
algorithms detect changes between on-star and off-star observations simply by
comparing the amount of energy detected in each observation. But if a faint
alien transmission overlaps in the sky with earthly noise, a basic
energy-detection algorithm may mistakenly discount everything it sees as
humanmade noise.

researchers hope artificial intelligence will be better than rigid energy-detection
algorithms at detecting subtle changes between on- and off-star observations.
While at the Berkeley SETI Research Center, applied machine learning researcher
Yunfan Gerry Zhang taught an AI to recognize radio interference from human
technology by showing it thousands of observations from the Green Bank
Telescope. Using its learned sense of what earthly radio interference looked
like, the AI could accurately pick out humanmade
that was
mixed into on-star observations.

If such
an algorithm were to detect radio signals from a star that didn’t qualify as
humanmade noise, the AI could flag that star for researchers as a potential
source of alien transmissions. Zhang’s team presented the AI at the 2018 IEEE Global Conference
on Signal and Information Processing as a tool for finding oddities in future
SETI investigations.

Looking for lasers

Radio waves,
the focus of mainstream SETI, are not the only means of sending interstellar
messages. Aliens could also encode information in nanosecond laser pulses. Though
lasers were first suggested as potential interstellar beacons in 1961, most
SETI searches have followed Drake in looking for radio communications — partly
because radio waves are low energy, and so possibly a more
cost-effective way to package
interstellar mail.

optical light could also be a practical interstellar beacon if focused into a narrow
laser beam, argue proponents of this approach, called optical SETI or OSETI. Fast
laser flashes would be would be detected as a bunch of photons hitting the
telescope all at once, as opposed to the steady trickle of incoming photons
from background starlight. As a result, for the nanosecond duration of the
laser pulse, it could outshine surrounding stars. And no known astrophysical
sources produce nanosecond optical blips.

SETI is still in its infancy, or early toddler phase,” compared with radio
SETI, says Shelley Wright, an astrophysicist at the University of California,
San Diego. But if used in tandem with radio scans of the sky, OSETI efforts can
expand the search into entirely different mode of communication.

PANOSETI observatories field view
To take the search for alien laser signals to the next level, researchers have proposed building four dedicated PANOSETI observatories — two in the Northern Hemisphere, two in the south. The observatories’ collective field of view (projected onto the sky in this animation) would cover the entire observable night sky to keep a continual lookout for interstellar laser beacons.PANOSETI team

In July
2019, the VERITAS telescope array at the Whipple Observatory in Arizona joined
Breakthrough Listen. This telescope quartet was built to watch for brief
flashes of blue “Cherenkov” light generated by astrophysical gamma rays hitting
Earth’s atmosphere. But its fast cameras are also well suited to looking for
E.T.’s laser beams.

VERITAS Breakthrough Listen effort involves both new optical stellar
observations and a review of old VERITAS data. Already, some of those analyses
have garnered results, even if somewhat disappointing. Nine hours of observations
taken from 2009 to 2015 of Tabby’s Star — once suspected of holding an
alien megastructure in its orbit due to its bizarre periodic dimming (SN:
) — found no alien laser beacons, the researchers reported in the Astrophysical
Journal Letters
in 2016.

and colleagues hope to dramatically expand OSETI with new facilities. While previous
OSETI searches, including VERITAS, have targeted specific stars for only
minutes at a time, Wright’s team has drawn up a blueprint for four dedicated
SETI observatories to keep constant vigil for alien laser pulses across the
entire observable sky.

This observatory concept, dubbed
, was
described at the SPIE Astronomical Telescopes + Instrumentation meeting in
Austin, Texas, in July 2018. Each observatory would be a dome covered in 88
lenses with optical and near-infrared detectors. One pair of observatories in
the Northern Hemisphere would keep watch over the northern sky, while a second
pair in the south would keep tabs on the southern sky.

Two observatories in two different locations would have to keep watch over the same part of the sky to ensure that anything a single observatory detected wasn’t a glitch or an effect caused by local light pollution, Wright says — the same way a pair of far-flung LIGO detectors teamed up to detect cosmic ripples called gravitational waves (SN: 2/11/16). “Nobody would have believed LIGO without a secondary site,” she says. Double-checking potential detections would be absolutely crucial for a claim as extraordinary as receiving a greeting from E.T.