In February, astronomers announced the discovery of a new solar system with seven Earth-like planets circling a cool temperature, Jupiter-sized star named TRAPPIST-1. The star’s small size permits study of its planets’ atmospheres, which have temperatures suitable for liquid water that could support extraterrestrial life. The discovery also adds to a growing understanding in modern astronomy that exoplanets—planets that orbit stars other than our sun—are far more common than previously expected. We now know that 22 percent of sun-sized stars have an Earth analogue that orbits the habitable zone, with the nearest Earth-like planet within 12 light-years of our solar system. That’s a lot of possible worlds on which life, and intelligence, could exist. So, why haven’t we seen it?

Breakthrough Listen

Since it began in the 1970s, SETI (the Search for Extraterrestrial Intelligence) has  composed of a loosely organized—and often underfunded—group of astronomers and engineers, who devote themselves to finding intelligence elsewhere in the cosmos. Since the likelihood of finding a signal in the seemingly endless radio noise we receive from space is so low, SETI has remained on the fringes of mainstream astronomy. However, recent advances in observational technology, new funding, and innovative ideas about where to look for intelligent life are creating a renaissance in SETI research, thrusting it into the limelight.  UC Berkeley has been home to many innovative thinkers that have advanced the field of SETI over the last three decades, Now, a new laboratory in the Department of Astronomy called Breakthrough Listen is emerging as the command center for this new age of SETI observations.

The work of Breakthrough Listen takes place in a wall-less, spacious conference and office space on the second floor of the astronomy department in Campbell Hall. Established in 2014 through a $300 million grant from Russian billionaire and venture capitalist Yuri Milner, the advisory board of Breakthrough Listen includes Nobel laureates and science celebrities like Stephen Hawking. Breakthrough Listen is using the bulk of its funding to buy time on two of the world’s best radio telescopes, the Green Bank Observatory in West Virginia and the Parkes Observatory in Australia. The astronomers take turns, sometimes pulling all-nighters, to control the telescopes from a remote link on a laptop computer. They are also using the funding to improve their algorithms for detecting a signal, correct for interference from man-made noise, and deal with the signal distortion  caused by ripples in space-time.  The new funding source is a revolution for these SETI researchers who have maintained SETI as a side project throughout their careers but now have the money to be wholly devoted to the search.

Funding, however, is not the only hurdle these researchers had to overcome. For decades SETI surveys of transmissions from space have been viewed as pointless. Radio waves are the preferred medium for SETI surveys because of their range and the fact that a reasonably advanced civilization could use them to convey information (humans have leaked radio waves out of our own atmosphere since the 1940s). But the universe is vast and radio waves are emitted by many kinds of cosmic phenomena, including quasars, meteorites hitting our atmosphere, and even the Big Bang, which echoes indefinitely as cosmic background radiation. All this noise means there is a low probability of discovering something interesting.

To improve their odds, Breakthrough Listen is specifically targeting areas where intelligent life is more likely to exist: solar systems where exoplanets orbit the habitable domain around a star. They will be directing their scopes towards TRAPPIST-1 soon. Habitable worlds are being detected at an ever-increasing rate in modern astronomy, with new techniques and bigger data sets frequently becoming available. As Breakthrough Listen astronomers follow up on each new lead, their odds of making a discovery greatly improve.

Seven planets (b-h) of the recently discovered TRAPPIST-1 planetary system could harbor extraterrestrial life. While the planets are Earth-sized, the TRAPPIST-1 system is significantly smaller than our solar system. Design: Nicole Repina, Infographic data and images: NASA

Breakthrough Listen also studies anomalies that  other astronomers are unable to explain according to natural processes. One of those anomalies are fast radio bursts (FRBs), which are bright, unexplained pulses of electromagnetic activity detected from sources outside our galaxy. FRBs were first discovered in 2007, baffling empirical astronomers and theoretical physicists. At first, the widely accepted explanation of these phenomena was that FRBs are glimpses of a one time explosive event, like a supernova, the flash of energy when a very dense star falls into a black hole. In 2016, however, McGill astronomer Paul Scholz showed that some FRBs actually repeat at regular intervals, ruling out one-time occurrences like collisions or explosions. Danny Price, a postdoc with Breakthrough Listen, told me he is excited and optimistic about the possibility of observing FRBs. “We are like a command center,” Price told me. “We can follow up on these anomalies.  With the resources we have, we can find out what they are, and what they mean.”

Another oddity being studied by Breakthrough Listen is Tabby’s star. Also known as the WTF star (for “where’s the flux?”), this star captured the public’s imagination in 2015 when astronomers announced that something massive, possibly artificial, was in its orbit. Jason Wright, a visiting scholar on the Breakthrough Listen project, is one of the authorities on this exciting new find. Wright earned his PhD in astrophysics at UC Berkeley, where he developed methods to detect exoplanets through the shadows they produced as they move in front of distant stars. “While doing so,” Wright tells me, “I once noodled around with, and thought for a day or two, about looking for evidence of extraterrestrial civilizations on those exoplanets, or more specifically, around them.”

Rather than look for radio waves being transmitted by alien civilizations—as SETI astronomers had been doing since the 1970s—Wright  proposed that astronomers apply the same technologies to look instead for shadows being created by an artificial structure called a Dyson sphere. Named for Freeman Dyson, the physicist who proposed their existence, a Dyson sphere is a massive solar panel, the size of an entire solar system, that advanced civilizations could use to meet their energy needs. This artificial structure could be so large that its shadow would be visible as it passes in front of its host star.




Atmospheric absorption of electromagnetic waves is dependent on wavelength. Visible light and radio waves are observable from Earth using optical or radio telescopes, whereas infrared, ultraviolet, X-ray, and gamma-ray radiation are mostly blocked by Earth’s atmosphere and are best observed from space. Design: Nicole Repina,Infographic data: NASA

It is possible that astronomers have found their first Dyson sphere. In 2014, NASA launched the Kepler Mission to continuously monitor starlight from thousands of nearby stars. The data from this mission became the foundation for furious searching by professionals and amateurs alike for the dips in light curves characteristic of exoplanets. Throughout the course of the Kepler mission, hundreds of new planets have been discovered, but as some amateurs pointed out,  one particular star stood out from the rest, seeming to fit Wright’s predictions about the dimming patterns produced by a Dyson sphere.

KIC 8462852, known colloquially as Tabby’s star (after Tabetha Boyajian, first author of the publication on the star’s behavior), shows irregular and intense dimming—more extreme than any other transiting event observed thus far. To put this exceptional behavior in context: when a planet the size of Jupiter—about as big as a planet can be—passes in front of a star, it blocks about 1 percent of that star’s light. In contrast, Tabby’s star has an incredible dimming pattern of up to 20 percent of its light output. That means an object 20 times larger than Jupiter is moving in front of it. Furthermore, the pattern of the dimming is irregular, not what you would expect from a comet field or an exoplanet.

Until recently, the leading hypothesis was that this extreme dimming was due to something fractured, like a cloud of asteroids or the remnants of a planetary collision. If this were true, this field of debris would absorb starlight and heat up. To check, astronomers observed Tabby’s star through a telescope that collects infrared light. Where they expected to see a broad field of heat emanating from the debris, they found the opposite. What ever is orbiting Tabby’s star doesn’t give off infrared radiation. Instead, it appears to absorb radiation.

Many citizen scientists think this absorption of radiation is a clear sign of a Dyson sphere. After all, it is the same pattern you would expect out of a giant energy collecting structure. Most astronomers, however, are reluctant to concede to that view. Jason Wright himself is skeptical. “It’s definitely something new,” he tells me, “and that is really what is special.” Wright is now working with Breakthrough Listen to study Tabby’s star, but so far they have not detected any extraordinary radio transmissions. “That doesn’t necessarily mean that there is nothing to be found,” says Wright. “Actually, we may have only begun to scratch the surface.”

When a distant planet crosses in front of (transits) its parent star, the dip in light intensity can be detected from Earth. The exoplanet’s radius is proportional to its transit duration. This method for exoplanet detection, called transit photometry, is used in the NASA Kepler Mission, including the KIC 8462852 (Tabby’s star) discovery. Design:Nicole Repina, Infographic data and images: NASA

Screensavers, unite! 

Searching for signs of intelligent life, it turns out, is a lot more complicated than it appears. Understanding why is not exactly intuitive, so astronomers often employ the metaphor of a desert road trip: you are driving across the desert and you are flipping through the radio dial in search of music. You flip through approximately 200 channels, and then, score! Bob Marley! The signal is momentary, however, and the good tunes disappear when you cross the next dusty pass. There’s nothing else on the radio but static, so you give up and enjoy the view.

Now compare this to the search for extraterrestrial intelligence. The situation is similar: a radio antennae pointed at an object picks up radio signals at various frequencies. The job of the radio astronomer is to flip through those channels until something interesting comes up (hopefully, not Bob Marley). But the astronomer’s  situation is far more complex than the desert road-tripper. For each celestial object a modern radio telescope records literally billions of frequencies, which are recorded simultaneously, leaving behind a mind-boggling amount of data. Celestial objects also move, often rapidly, towards or away from Earth. Signals emanating from those worlds are thus distorted by space-time, as described by the theory of relativity, in what astronomers call redshifts. So, to find the signal of interest coming from another world, a SETI researcher has to search through billions of radio frequencies multiplied by each of their possible redshift corrections. Even simple SETI searches quickly become problems so complex that they could crash a super computer. In the end, maybe we should just give up and enjoy the view!

This insurmountable computational mountain has posed one of the greatest obstacles to SETI research. By as early as the 1990s, SETI researchers had amassed more data than they could ever hope to analyze. In the last two decades, however, the program has taken strides in its ability to sift trough SETI data. One landmark project that revolutionized SETI data analysis was SETI@HOME, which was initiated by UC Berkeley astronomer David Werthimer and computer scientists David Anderson and Matt Lebovsky in 1997.

SETI@HOME was the first ever distributed computing platform. Distributed computing allowed SETI software to borrow and compile space on private citizen’s CPUs into one massive super computer capable of running computations more complex than any single machine at its time. SETI@HOME became popular during the time when computers reverted to a screen saver while not in use. SETI@HOME worked just like a screen saver, except that instead of displaying flying toasters—a  popular screen saver in its day—your computer connected to the SETI@HOME server and helped sift through radio astronomy data. SETI@HOME ran until 2005. Although it didn’t find an extraterrestrial civilization, it was successful in invigorating the citizen science community to contribute to SETI research. In total, 5 million citizen scientists participated in donating computer time to SETI@HOME, giving SETI researchers the capacity to carry out the world’s largest computation.

SETI engineers at UC Berkeley continue to develop SETI@HOME’s software for research. The software has evolved into an open-source infrastructure known as BOINC (Berkeley Open Infrastructure for Network Computing), which can be applied to a variety of studies. BOINC is currently being used in climate modeling (, HIV, malaria,  and cancer research (World Community Grid), particle physics (LHC@home), gravity waves (Einstein@home), and protein structure determination (Rosetta@home). The new software and growing base of donated computing space is being tweaked and perfected by engineers at Breakthrough Listen to comb through data sets with greater accuracy and efficiency.

What it means to not be alone 

Assuming that we are not alone in the universe, it seems increasingly likely that SETI researchers will turn up an important discovery in the not-so-distant future. What will be the consequences of discovering intelligent life outside of Earth ? Will there be a paradigm shift in human consciousness, politics, and technology? These questions have been tinder for the science fiction imagination.  I asked the real life SETI astronomers I spoke with to speculate about what they thought the effects of such a discovery would be for society. The range of their answers is surprising.

Jason Wright is skeptical that a discovery of extraterrestrial intelligence would ripple throughout society in a very profound way. “Don’t get me wrong,” he explains, “I think it would be an apocryphal moment for science, but I think if you poll the general public about whether extraterrestrials exist, most people would say that they not only exist, but that UFOs are visiting us on a regular basis.”

Eric Korpela, director of SETI@HOME, sometimes doubts we will ever find a SETI signal. “It’s easy to be pessimistic,” he admits. “The fact that we haven’t found any obvious evidence of intelligent life yet suggests that intelligence is either rare, or short lived in our universe.”

“Aren’t there plenty of habitable world’s out there though, on which life could exist?” I ask Korpela.

“This is true,” he clarifies. “Maybe there is just a time limit on advanced societies after which they simply destroy themselves and sink into obscurity. It would be difficult to hear their messages if they are fleeting. I’m not a fan of this view, but it does seem like there are a lot of people in power now that are putting our survival at risk.”

Matt Lebofsky, an engineer who wrote much of the code for SETI@HOME, told me the discovery of extraterrestrials would be like the moon landing, only more profound. “After people saw the landing,” Lebofsky explains, “people said ‘huh so space exploration is possible.’ That led us into the space age. Discovery of an advanced intelligent life form would make people say ‘huh, that’s possible too’ and would open up a new age of technological innovation.”

“What if we don’t find anything?” I ask Lebofsky.

“Then we can learn from that too.”

With new funding, technology, and techniques, SETI is undergoing a renaissance that is moving this field from the fringes to the mainstream of modern astronomy research. However, it remains difficult to place SETI within the traditional confines of astrophysics, or within the boundaries of any scientific field for that matter. Andrew Siemion, director of Breakthrough Listen, says, “What sets SETI apart from other fields of science, is that it has an extremely low expectation value. What we are looking for may be exceedingly rare.” Siemion himself has worked on SETI since he was an undergraduate at UC Berkeley. After completing his PhD in astrophysics in the astronomy department at UC Berkeley, he took the position as director of Breakthrough Listen.

What has kept him devoted to SETI research all of these years?

“Sure, the expectation that we find something is very low,” Siemion says. “But if we do, it would be the most amazing discovery that humans could possibly make.”




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