It may sound cliche, but the question ‘Are we alone?’ is still one that captures the imagination of many people, including of course, scientists. With the now regular discovery of exoplanets orbiting other stars, the prospect that there may be other intelligent life out there somewhere (or any kind of life) has only become more exciting and compelling. When it comes to intelligent extraterrestrials, SETI is a name that has become part of our modern culture, the Search for Extra-Terrestrial Intelligence. SETI focuses on looking for radio and optical signals that could originate from an advanced society, a technique that in itself has generated much debate. After several decades of searching, a definitive signal has yet to be found, but there have been tantalizing possibilities. Unfortunately, none of those have yet panned out as the signal. Now, another interesting radio signal is making the news – could it be the evidence scientists are looking for or is it another dead-end?
The new signal was first reported by Paul Gilster in Centauri Dreams on Aug. 27, a “strong” radio signal detected in the direction of a star in the constellation Hercules. The detection was made by the RATAN-600 radio telescope in Zelenchukskaya, Russia on May 15, 2015, but was only recently made public by Russian astronomers. The discovery, led by Nikolai Bursov of the Russian Academy of Sciences’ Special Astrophysical Observatory, will be discussed in more detail at a meeting of the IAA SETI Permanent Committee, during the 67th International Astronautical Congress (IAC) in Guadalajara, Mexico, on Tuesday, Sept. 27th, 2016.
The star that the signal is purported to have come from is called HD164595, which is almost exactly the same size as our Sun and a bit older. About 95 light-years away, it is 0.99 solar masses and estimated to be 6.3 billion years old. The star’s metallicity is also very similar to that of our Sun. The star has at least one known exoplanet, HD 164595 b, which has a 0.05 Jupiter mass. It orbits its star in 40 days, and is likely to be a “warm Neptune.” There may still be other planets, as yet undetected.
Those facts themselves make this star interesting, but what about the radio signal itself? It was detected on May 15, 2015, at 18:01:15.65 (sidereal time), at a wavelength of 2.7 cm, which is equivalent to a frequency of 11 GHz. The receiver of the RATAN-600 radio telescope has a bandwidth of 1 GHz, which is a billion times wider than the bandwidths typically used in SETI searches. It’s also 200 times wider than a television signal, with a strength of 0.75 Janskyns, which is considered weak. The nature of the signal brings to mind two possibilities, if it was actually alien.
First, the signal is being sent out in all directions. The required power would be 1020 watts, or 100 billion billion watts, in order for us to have found it with the RATAN-600. That is a lot of power, hundreds of times greater than all of the sunlight falling on Earth. Second, the signal was being aimed directly at us. That would require less power, but still more than a trillion watts. Both possibilities would require technology far beyond what we currently have on Earth.
The RATAN-600 is also an unusual radio telescope, consisting of a ring on the ground which is 577 meters in diameter. The past of the sky to which it is the most sensitive is a “beam shape,” elongated north-south, and 20 arcsec by 2 arcmin. The signal however, seemed to come from the east-west direction.
From all accounts so far, including from SETI, this is more likely to be a case of terrestrial interference or possible a natural astronomical phenomenon. The fact that the signal was only heard the one time (so far) in 2015 doesn’t help. SETI requires a signal to be detected more than once, preferably by multiple radio telescopes, for that signal to be considered truly compelling.
“Their receiver was set up to gobble up a huge chunk of the radio dial at once,” said Seth Shostak, senior astronomer at the SETI Institute. “Generally, SETI looks for narrow-band signals … that’s like your laser pointer, which, although it has very little power, makes a highly visible spot because it’s all in one wavelength range.”
Starting on Aug. 28, astronomers started using the Allen Telescope Array (ATA) to listen to the star. So far, the signal has not been heard again. In this way it is reminiscent of the famous ‘Wow! signal‘ from Aug. 15, 1977, heard by the Big Ear radio telescope of Ohio State University. That signal was only heard once and still has not been explained. The full range of frequencies still need to be checked however.
There is also the question of why the Russian astronomers didn’t alert other scientists with SETI at the time. It is standard protocol within the SETI community that if a candidate signal is found, others are notified immediately so that they can try to detect it as well. That didn’t happen in this case.
The research group METI International will also try observing HD 164595, using the Boquete Optical SETI Observatory in Panama. As president Doug Vakoch explained in GeekWire:
“Standard SETI protocols call for confirmation of possible signals from a separate observatory. This helps ensure that the original signal didn’t arise from a technical glitch in the original observatory, and it helps rule out a hoax perpetuated by some enterprising graduate students targeting a SETI experiment. In the past, plans for SETI follow-up observations have focused on confirmation of the original signal, seeking a repeat signal at the same frequency. That’s a critical step for confirmation – and we don’t yet have evidence that this sort of follow-up has happened for HD 164595. In addition, we need to be alert to the possibility than if we do really find a signal from an advanced civilization, they are also transmitting at other frequencies than the one where we first detected them. That’s why it’s so important to prepare for follow-up SETI observations at both radio and optical frequencies, to be launched as soon as we detect a credible candidate signal at any frequency.”
As also noted by Shostak:
“This is a bit of a puzzling story, as the Russians found this signal a year ago or so, but just didn’t let others know. That’s not good policy, as what you really want is confirmation at another telescope, but … Is it real? The signal may be real, but I suspect it’s not ET. There are other possibilities for a wide-band signal such as this, and they’re caused by natural sources (or even terrestrial interference).”
There was also the case last year where a possible radio burst signal, detected by the Parkes Observatory in Australia, was found to actually originate from a microwave oven in the facility.
The Breakthrough Listen project also aimed the Green Bank Telescope at the star, but so far has heard nothing.
“Our GBT observations did not detect ongoing emission from the direction of HD 164595. Single-epoch transients are by their nature hard to confirm or deny, illustrating the need for confirming follow-up, either at a later time, or as part of the observing strategy.”
*As this article was being written, a statement was released by the Russian Academy of Science. The translation follows (via Google Translate):
“August 30, 2016 in a number of media reports about the possible detection of the RATAN-600 radio signal associated with the activity of an extraterrestrial civilization, in this connection, we consider it necessary to give an official comment.
Over the past few years, staff SINP MSU (Institute of Nuclear Physics of Moscow State University named Skobeltsyn) jointly c SAO staff conducted exploratory work on the study of astronomical objects – SETI candidates (Search for Extraterrestrial Intelligence). SETI – the common name of projects and activities to search for extraterrestrial intelligence. The program is focused on the search for artificial radio emission. Research is being conducted on the RATAN-600 using a broadband continuum radiometers in the frequency range 1-22.7 GHz. Conducting such observations on RATAN-600 has been made possible thanks to its large collecting surface – thousands of square meters, which is why the high sensitivity allows the telescope to search for radio signals are extremely weak in the universe, which include SETI objects. The objects of study for this program are Sun-like stars with planets and Sun-like stars, planets whose presence is unknown.
Under this program, in 2015 on one of the objects (the star HD164595 system in the constellation of Hercules), it was detected interesting radio signal at a wavelength of 2.7 cm. The processing and signal analysis revealed that the most likely, it’s still a signal of terrestrial origin.
With regard to other research facilities on RATAN-600, it is currently too early to talk about the reliability of the scientific results. The measurements can evaluate radio emission study areas just to the upper limit of detection. With confidence we can say that the search signal is not detected.”
And that’s where we currently are. We probably won’t know much more until perhaps the IAC meeting next month, or if by chance the signal is detected again. As it stands, the signal was most likely terrestrial interference, as has happened often before.
You can track SETI live as it searches for this or other signals on its website.