Is a mysterious radio signal received by the Arecibo Observatory in Puerto Rico a message from another civilization in our galaxy? Scientists at the Planetary Habitability Laboratory (PHL) say it's highly unlikely, but the peculiar signals coming from the red dwarf star Ross 128 are raising speculation because their origin remains a mystery.

According to Abel Méndez, director of the PHL at the University of Puerto Rico at Arecibo, the signals from the star, which is 11 light years from Earth in the constellation of Virgo, were picked up by the giant Arecibo radio telescope on May 13 at 00:53 GMT. The small, dim star was under observation as part of a study of red dwarf planetary systems, which included Gliese 436, Ross 128, Wolf 359, HD 95735, BD +202465, V* RY Sex, and K2-18.

Méndez says that only Gliese 436 and K2-18 are known to have planets, but the other stars were studied in April and May to learn more about their radiation and magnetic environments that might provide clues as to the presence of dark companion stars or planets. Ross 128 has no known planets or companions, but is already of interest to astronomers because it's classified as an active flare star due to its tendency to suddenly increase its luminosity for a few minutes.

Ross 128 was one of a number of red dwarf stars being surveyed (Credit: PHL)

Ross 128 was observed by Arecibo Observatory in the 4 to 5 GHz C band on May 12 at 8.53 pm local time. Nothing unusual was seen at the time, but when the data was analyzed two weeks later unusual signals were picked up in the 10-minute dynamic spectrum. The signals consisted of non-polarized pulses that showed signs of being periodic with strong dispersion-like features. Periodicity is one sign of an intelligent signal, though many natural phenomena, such as pulsars, possess it.

Having eliminated radio interference from Earth, Méndez and his team have narrowed the source of the signal to three possibilities.

The first is that the signals are from Ross 128. If so, then the red dwarf star is producing something very like Type II solar flares, but such flares happen at much lower frequencies and don't show so much dispersion. This suggests that the source is farther away or there is a dense electron field present – possibly in the stellar atmosphere.

The second likelihood is that the signals aren't coming from Ross 128, but from an object along the same line of sight, but closer or farther away. However, the area around the star isn't very densely populated and there aren't any likely suspects in the vicinity.

The third possibility is that the source of the signal is much closer to home, perhaps a satellite in a high orbit around the Earth that is either making rogue transmissions or is inadvertently reflecting radio or radar signals back to the ground. The trouble is, while such things have occurred, they've never involved bursts of this nature.

And then there is the obvious question raised by the periodic nature of the signal. It hasn't been ruled out, but no one is holding their breath.

"In case you are wondering," says Méndez. "The recurrent aliens hypothesis is at the bottom of many other better explanations."

The PHL team is currently working on confirming the signals and gathering more data to determine their origin. Though the incoming radio waves are too weak to be detected by most telescopes, PHL managed to book time at Arecibo on July 16 for more observations. Meanwhile, SETI Berkeley is using the Green Bank Telescope to tune in on Ross 128, as is the SETI Institute's Allen Telescope Array.

"Results from our observations will be presented later that week," says Méndez. "I have a Piña Colada ready to celebrate if the signals result to be astronomical in nature."

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