In 1967 researchers Jocelyn Bell Burnell and Antony Hewish discovered an astronomical anomaly: radio-wave pulses that repeated every 1.33 seconds, originating from the same location in the sky. While they “did not really believe that we had picked up signals from another civilization”, they did admit to considering the possibility, given the signals were unlike anything ever detected before – so much so that they named the signal LGM-1, a tongue-in-cheek acronym for “little green men”.
When more pulsating sources were later discovered, and an entirely natural “lighthouse model” explaining the anomaly as a rotating neutron star was put forward, the ‘extraterrestrial civilisation’ explanation was well and truly left behind.
However, Belgian researcher Clément Vidal believes that the reasons for dismissing the ET hypothesis were not necessarily entirely valid, and perhaps the idea should be revisited. In a paper titled “Pulsar positioning system: A quest for evidence of extraterrestrial engineering“, he runs through various elements of how pulsars could be used as navigational beacons, similar to how in recent decades GPS has become ubiquitous for our own navigation, and what that means for both SETI-related questions, as well as our own future in space, both in terms of navigation and communication:
X-ray pulsar-based navigation (XNAV) is comparable to GPS, except it operates on a galactic scale. I propose a SETI-XNAV research program, to test the hypothesis that this pulsar positioning system might be an instance of galactic-scale engineering by extraterrestrial beings. The paper starts with a critique of the rejection of the extraterrestrial hypothesis when pulsars were first discovered, continues with some highlights on the rich pulsar phenomenology, and their usefulness for various purposes. The core section proposes lines of inquiry for SETI-XNAV, related to: the pulsar distribution and power in the galaxy, their population, their evolution, possible pulse synchronizations, pulsar usability when navigating near the speed of light, decoding galactic coordinates, directed panspermia, and information content in pulses. Even if pulsars are natural, they are likely to be used as standards by ETIs in the galaxy. Such a common galactic timing and positioning standard have deep consequences for SETI and METI. I discuss potential policy issues, as well as benefits for humanity, whether the research program succeeds or not.
Vidal notes that while “normal” pulsars have a pulse period of 0.5 second on average, a small subset (around 10% of all pulsars) have a period between 1.4ms and 30 ms (known as “millisecond X-ray pulsars” (MSPs). This latter, short wavelength pulsar type is an ideal candidate for using as a ‘galactic positioning system’, as not only are they detectable with small, low-cost equipment (as opposed to a 20+ metre radio dish for normal pulsars), but they offer unbelievable accuracy relative to galactic distances: “a probe or seed could go anywhere in the galaxy, with an accuracy of 100m!”
Vidal also notes that MSPs distribution in space “is isotropic, while normal pulsars are more concentrated in the galactic plane”. He asks what is the likelihood for this to happen naturally, and whether this distribution spread is possibly another indication of the involvement of alien engineers.
To sum up, this paper draws two major conclusions, one to be expected, the other uncertain. First, all pulsars could be perfectly natural, but we can reasonably expect that civilizations in the galaxy will use them as standards (section 6). By studying and using XNAV, we are also getting potentially ready to receive and send messages to extraterrestrial intelligence in a galactically meaningful way. From now on, we might be able to decipher a first level of timing and positioning metadata in any galactic communication.
Second, what remains uncertain is whether the pulsar positioning system is natural or artificial. We put forward the SETI-XNAV quest to answer this issue. It draws on pulsar astronomy, and navigation and
positioning science to make SETI predictions. This concrete project is grounded in a universal problem and need: navigation. Decades of pulsar empirical data is available, and I have proposed 9 lines of inquiry to start the endeavor (section 5). These include predictions regarding the spatial and power distribution of pulsars in the galaxy, their population, their evolutionary tracks, possible synchronization between pulsars, testing the navigability near the speed of light, decoding galactic coordinates, testing various directed panspermia hypotheses, as well as decoding metadata or more information in pulsar’s pulses.
To critics of the proposal that pulsars might be navigation beacons, Vidal asks them to imagine that we found strange time-keeping devices well-distributed around Mars, beaming information that could easily be used as a ‘Mars Positioning System’. “Wouldn’t we be compelled,” he asks, “to explore the hypothesis that extraterrestrial intelligence is at play? This is exactly the current situation with millisecond pulsars, but on a galactic scale.”
And in any case, he notes, even if pulsars are entirely natural, they might still be used as navigation beacons by one species at least: us. With numerous scientific missions proposed to send probes not only throughout our solar system, but also beyond – such as Russian billionaire Yuri Milner’s ‘Breakthrough Starshot” quest to send a probe to Alpha Centauri – precise space navigation is an important topic for the new epoch of space travel. And pulsars, he notes, “are currently the best option to navigate the solar system and the galaxy with high accuracy”, and so the topic is definitely worthy of further research.