The Weird! Signal from Ross 128 detected in the May 2017 campaign (enclosed in the red frame).

Last week we distributed a press release announcing the Planetary Habitability Laboratory’s new collaboration with other observatories to study the red dwarf stars Barnard’s Star and Ross 128. We wanted to observe Barnard’s Star because it is a nearby star that might have planets and is currently being observed by the Red Dots project. We also wanted to observe, again, Ross 128 because in our previous observing campaign performed in May 2017 using the Arecibo Observatory we detected some peculiar signals from this star. Our project using the Arecibo Observatory, the world’s most active and most sensitive single-dish radio telescope, was originally aimed at searching for radio emissions from red dwarf stars intended to understand their stellar activity and any star-planet interactions.

Our follow-up observations of Ross 128 got much more attention from the press than we expected, although not necessarily for the right reasons. Based on our observations, we proposed three main explanations for the source of the strange signals from the star: (1) unusual stellar activity, (2) emissions from other background objects, or (3) interference from satellite communications.

Each of these potential solutions has its own problems, and so the mystery here was that we were not able to accurately distinguish between these working hypotheses. There were other less likely possibilities, such as ground radio interference, data processing errors, among several others.

However, many people were more interested in the signals as potential proof of transmissions from an extraterrestrial intelligent civilization. Statistically, this is always the last consideration, not because such civilizations are impossible, we humans are an example, but because other possibilities had frequently arisen and no extraterrestrial civilizations have been detected yet. Nevertheless, scientists need to be open to all possibilities and explore them. The Search for Extraterrestrial Intelligence (SETI) is a field of research that is part of astrobiology, and as such pursues finding signatures of life elsewhere in the galaxy. The SETI Berkeley Research Center at the University of California, and the SETI Institute are experts in this field.

There are many other examples where strange signals detected from different observatories resulted in the discovery of new astronomical phenomena or had a mundane explanation. For example, pulsars, which were originally referred to as LGM (Little Green Men), are fast rotating neutron stars. Peryton observations at Parkes Observatory in Australia were later shown to be caused by a malfunctioning microwave oven. Other strange signals are still a mystery, such as the recently detected Fast Radio Bursts (FRB), which the Arecibo Observatory helped to confirm and was essential in establishing their extragalactic origin.

Other unexplained signals, like the Wow! Signal, are commonly cited outside of academia to be proof of extraterrestrial communications. Unexplained here does not mean inexplicable; it just means we are not able to tell which is the precise source from many possibilities.

This was precisely the case of our signal from Ross 128, which we now call the Weird! Signal. We discussed our results with many other radio astronomers, but came up with no definitive answers. This finally motivated us to request the help from SETI Berkeley and the SETI Institute teams; both of which have a lot of observational experience and know very well the various kinds of terrestrial radio emissions.

Given the attention the story received from the media, we launched a public survey to ask people on the possible explanations of the Weird! Signal. The purpose of this survey was not in any sense to try to solve the mystery, but to involve the public in the excitement of real-time science.

Nine possible explanations for the Weird signal were given to the public in the survey: (1) stellar activity, (2) other astronomical source, (3) a satellite, (4) local interference, (5) instrumental glitch, (6) error in data acquisition, (7) error in data processing or calibration, (8) pattern in noise or (9) signal from aliens (a tenth possibility, “other explanation” was also included).

Nearly 800 people participated in this informal survey (including more than 60 astronomers); the consensus was that the most likely explanation was either (1) or (2), namely an astronomical phenomenon (see figure below). Causes related to radio interference or instrumental failures were considered most unlikely. This is interesting since in the absence of solid information about the signal, most astronomers would think that these would probably be the most likely explanation.





Results of a survey conducted during the week while the Weird! Signal was investigated.

Also interesting is the fact that a non-negligible number of participants in the Survey (~200) thought the most likely explanation of the signal was that of a communication with an Extraterrestrial Intelligence (ETI). However, a similar number thought that this would only happen “in our craziest dreams”. Although we do not necessarily share none of these opinions, these results reflect the still high expectations the public has on the possibility of contacting ETI.

After a careful analysis of the observations we performed last Sunday from the Arecibo Observatory, together with SETI Berkeley using the Green Bank Telescope and the SETI Institute’s Allen Telescope Array, we are now confident about the source of the Weird! Signal. The best explanation is that the signals are transmissions from one or more geostationary satellites. This explains why the signals were within the satellite’s frequencies and only appeared and persisted for Ross 128; this star is close to the celestial equator where many geostationary satellites are located. This fact, though, does not yet explain the strong dispersion-like features of the signals (diagonal lines in the figure); however, It is possible that multiple reflections caused these distortions, but we will need more time to explore this and other possibilities.





Location of Geostationary satellites operating between 4-8 GHz in the same region of the sky as Ross 128 (yellow dot).

Credit: Enriquez et al. (SETI Berkeley), http://seti.berkeley.edu/ross128.pdf

The Planetary Habitability Laboratory of the University of Puerto Rico at Arecibo made many new friends from this experience. We started coordinating efforts with the Red Dots team on their search for planets around nearby stars. We had the cooperation of AAVSO and other observatories with follow-up observations. Our students from the University of Puerto Rico could be involved in the scientific process, attending observations at the Arecibo Observatory and conducting data reduction. Such an experience is invaluable to our future scientists.