Last week the internet was abuzz with rumors of a strange star that some suggested might host an extraterrestrial construction. Astronomers say that scenario is a slim possibility. A more likely explanation is that the weird star, called KIC 8462852, is orbited by a swarm of comets, which is a pretty interesting idea on its own. But either way, this intriguing star might never have been found. The oddball was just one of thousands of stars being monitored by NASA’s Kepler telescope, which searches for the telltale dips in a star’s light caused when exoplanets pass in front of it. Computers spot most of the promising planet candidates in the data, but this star would have fallen through the cracks if volunteer citizen scientists had not flagged its unusual signature. “This wouldn’t have been picked up by a computer algorithm,” says Yale University astronomer Tabetha Boyajian, who manages the Planet Hunters crowdsourcing project to analyze Kepler’s data. “We weren’t looking for something like this.”
The volunteers’ human eyes noticed that the light from KIC 8462852 sometimes got fainter by as much as 20 percent. Typical stars in the Kepler field dim by about 1 percent, and even then it takes a very large, Jupiter-size exoplanet to cause such a decrease. And whereas exoplanets create dimming at regular intervals, KIC 8462852’s dips were not periodic but random. When the Planet Hunters volunteers referred the star to astronomers for further review, Boyajian at first doubted the observations. “The first thing we think is there’s something wrong with the data,” says Boyajian, the lead author on an arXiv paper about the bizarre star. But her team rigorously checked their equipment and found no technical errors to explain the peculiar light signal. “These [dimming] events last from a couple of days to a couple of months. And that’s weird,” Boyajian says.
The most plausible explanation Boyajian’s team came up with was exocomets. Most observed space objects—like planets, comets and asteroids—are roughly spherical. But the way the light is altered around KIC 8462852 cannot be explained by a lone circle moving across the face of a star. A cluster of exocomets in an irregular clump, possibly drawn in by a neighboring star, could cross the star and cause varying dimming of light. “The exocomet theory really is the best theory at this point only because it has the least amount of conflict with the data we’ve currently got,” Planet Hunter and amateur astronomer Daryll LaCourse says.
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Others, such as astronomer Jason Wright of The Pennsylvania State University, think the exocomet explanation is contrived. Based on the light signal from the star, Wright floated an incredibly unlikely alternative explanation: artificial constructs could be orbiting the star. “People have been thinking about the possibility of detecting artificial structures with Kepler,” says Andrew Siemion, director of the Berkeley SETI Research Center. (SETI is short for search for extraterrestrial intelligence.) “In this case the theory has come to the fore because now we have a very strange looking light curve and we’re struggling to find an explanation for it.”
Most of what SETI observes are nearby stars and galactic centers, but every now and then SETI finds a wildcard. “There’s this final category of things that we call exotica—strange objects that for some reason don’t really fit the model of their class,” Siemion says. “They might be an anomalous pulsar or a quasar that shows odd variability. This star falls into that category.”
Siemion, Wright and Boyajian all want further observation of this strange star in order to tease out its mysteries. To do that they plan to use the Green Bank Radio Telescope in West Virginia. If lucky, they might also be able to tap data from the Transiting Exoplanet Survey Satellite (TESS) after its planned 2017 launch, which takes place when the suspected exocomets’ next passage is predicted to occur. It is a close window for using TESS and there is no guarantee the satellite would pick up the star’s signal.
The more intriguing, yet highly unlikely outcome, would be the detection of a very ordered, narrow-band radio emission less than a hertz wide, which would indicate the presence of technology or an artificial structure. Natural particles that emit electromagnetic radiation move in random directions, causing the emissions to be spread out in frequency or wavelength. Radiation emanated by technology, however, is very ordered and focused in a single direction, making it very compressed. “When we do a SETI search, we look for this artificial compression or contraction of signal in frequency, wavelength or time,” Siemion notes. “It’s [KIC 8462852] the single-most interesting star from a SETI perspective,” he adds.
It still remains an incredibly distant possibility that Kepler has truly picked up on artificial structures orbiting a distant star. Yet whatever the explanation for KIC 8462852’s signal is, it promises to be an interesting story—and one that astronomers have citizen science to thank for.