When the best hypothesis is aliens, the best place to test it is the Green Bank radio telescope.
If there’s intelligent life somewhere else in the universe, it lives on planets orbiting other stars. Planets in other systems have been hard for us to find until recently—we didn’t find our first until 1992. Those “exoplanets” are hard to see, because the stars they orbit outshine them. But if a planet’s path carries it between its star and Earth, we now have instruments sensitive enough to notice the less-than-1-percent dip in brightness caused by such a mini-eclipse.
The best place to take measurements that precise is from space, outside the Earth’s thick, wavy atmosphere. So in 2009, NASA launched the Kepler space observatory to monitor the brightness of 150,000 stars in a small, fixed area of the sky—an area about the size of your open hand at arm’s length. Through mid-2013, Kepler transmitted data every day back to Earth, where computers and astronomy enthusiasts reviewed it for patterns and surprises.
Among the many stars with regular, minuscule dips in brightness, citizen scientists noticed something perplexing: one star with irregular dips, sometimes up to a dramatic 20 percent. A Sun-sized star less than 1,500 light-years away, it was designated KIC 8462852, but was soon dubbed “Tabby’s Star” for Tabetha Boyajian, the Yale postdoc who came to publicize it.
Meanwhile, Jason Wright, a Pennsylvania State University astrophysicist, had been conducting an unusual Search for Extraterrestrial Intelligence (SETI) hunt—not for the communication signals SETI usually seeks out, but for other signs of advanced alien technology, something along the lines of swarms of energy-collecting satellites surrounding stars. Wright was drafting a paper in the fall of 2014 conceding that the Kepler observatory had found no such thing when Boyajian showed up at Penn State to give a talk. She showed him the KIC 8462852 data. “This stumps me,” he recalls saying.
None of the hypotheses—ideas like a pack of comets passing by through interstellar space—explained all of the observations convincingly. So Wright put his idea out there: Maybe Tabby’s Star was actually surrounded by a swarm of alien satellites. Since no one had a more plausible hypothesis, Wright and Boyajian decided to listen for SETI-type communication signals coming from the star.
Astronomers everywhere got interested. “Getting telescope time in astronomy is often difficult,” Wright says. “But people heard that something weird was happening, and there were people with their precious 8 or 10 hours of darkness emailing us saying, ‘I can spare 15 minutes,’ or ‘45 minutes’ to give us data. In terms of the number of telescopes all following a single event, it was one of the biggest events going on.”
And in late 2016, the Breakthrough Listen SETI project devoted three 8-hour periods of prized observation time at the best SETI telescope there is: West Virginia’s Green Bank radio telescope.
“Green Bank is at just the right frequency for radio SETI, which happens at low gigahertz—higher than the radio dial but low for astronomy,” Wright says. “Not only is it a gigantic, lower-frequency telescope, but you can point it anywhere in the Northern Hemisphere. It’s the only such gigantic telescope we could point at Tabby’s Star.”
It will come as no surprise that Green Bank did not discover aliens harvesting energy from Tabby’s Star. Based on new data, NASA posted a media release in October 2017 advancing the hypothesis of an uneven dust cloud moving around the star as the cause of at least some of the observations. “This flies in the face of the ‘alien megastructure’ idea and the other more exotic speculations,” NASA’s post reads.
Still, those who are eager for company in this vast universe can take heart. Kepler found more than 2,300 exoplanets in just its little section of space, 30 of which are about Earth-sized and orbit in their stars’ habitable zones—meaning, they could harbor something along the lines of life as we know it. Estimates are that our Milky Way galaxy may host more than 10 billion Earth-sized, rocky planets orbiting the habitable zones of Sun-like stars. The search continues and, when aliens are found, Green Bank will likely play a key role.