A report of a possible SETI signal that triggered a flood of news stories over the weekend shows the inherent problems with announcing a discovery that’s potentially historic—while at the same time being very unlikely.
In the three days since a story appeared on the respected Centauri Dreams website about an abnormally strong burst of radio energy from a star 94 light-years away, many astronomers have expressed doubt that the signal came from extraterrestrials. In fact, neither the Centauri Dreams story nor the Russian astronomers who reported the observation make such a claim.
A team using the RATAN-600 radio telescope in southern Russia was systematically observing a list of around 30 SETI candidate stars last year when they detected an anomalously strong signal from a sunlike star in the constellation Hercules. Other researchers had previously found a planet roughly the mass of Neptune around this star, which is designated HD 164595.
Unfortunately, the signal detected on May 15, 2015 was never repeated, although HD 164595 was observed a total of 39 times. The Russian astronomers subsequently tried to rule out other possible natural or manmade sources for the radio signal. “We needed a year of work for accurate estimation of the noise level,” according to team member Alexander Panov of Moscow State University, “and finally we decided that we [had] something strange.” Last week the team e-mailed other SETI researchers around the world to tell them of the observation, which they also plan to discuss at a scientific meeting next month.
Most astronomers remain skeptical. Seth Shostak of the SETI Institute, who writes in the current issue of Air & Space about another false alarm in 1997, points out that the RATAN-600 signal spanned a broad swath of the radio spectrum, unlike the narrow-band transmissions one might expect from aliens trying to communicate across vast reaches of space. In fact, writes Shostak, it’s not even certain the signal came from HD 164595.
Eric Korpela, director of the University of California at Berkeley’s SETI@home initiative, was even more dismissive in a post yesterday: “All in all, [the HD 164595 signal] is relatively uninteresting from a SETI standpoint…. SETI@home has seen millions of potential signals with similar characteristics, but it takes more than that to make a good candidate. Multiple detections are a minimum criterion.”
Andrew Siemion of Berkeley, principal investigator for the new Breakthrough Listen initiative, says that transient signals like the one detected by RATAN-600 “are really hard” for SETI to interpret, especially if they’re heard only once. His Breakthrough team happened to be in a meeting when the email about the Russian observation came in last week, and it was a fairly straightforward decision to turn the Green Bank Telescope in West Virginia to observe HD 164595, which they did on Sunday. They also searched the archive of past Green Bank observations, but in neither case did they find evidence of any strong transmission. According to the team’s preliminary analysis, “If the [HD 164595] transient…originates from beyond the Earth, then, given what we currently know of the parameters of the RATAN search, such events ought to be common. The fact that they are not frequently seen in continuum imaging surveys suggests that the RATAN transient is likely due to instrumental interference or to some other artifact of human technology.”
The SETI Institute’s Allen Telescope Array also has been observing the star in the last couple of days, also with no luck.
Did the Russian team overstep by even raising the possibility of a SETI detection—especially when, as Shostak writes in his Air & Space article, “any promising signal will become public knowledge immediately”? And why did they tell no one until more than a year after the observation? Siemion says he has some sympathy considering the enormous amount of work it can take to rule out possible sources of noise in the massive amounts of data produced by modern radio telescopes. Right now, he says, decisions about when and how to contact other SETI researchers with a possibly interesting result are “organic,” and depend on the circumstances.
SETI researchers have tried to establish post-detection protocols for what to do and say in the event of a possible discovery, but these are only loosely followed. “We have some work to do as a community” in this regard, Siemion says. Duncan Forgan, an astronomer and astrobiologist at the University of St. Andrews in Scotland, recently co-authored a paper that advises SETI researchers to use blogs, social media, and other means to communicate the goals and results of their research right from the outset. Say the authors, “Before any search is attempted, the researchers should be prepared for what is likely to be an unprecedented media onslaught.”