Pulsar Positioning System Pulsar Positioning System: A quest for evidence of extraterrestrial engineering Clément Vidal Center Leo Apostel Vrije Universiteit Brussel Krijgskundestraat 33, 1160 Brussels, Belgium http://www.clemvidal.com, [email protected] v2.0, 15 Oct 2017, to appear in the International Journal of Astrobiology Abstract: Pulsars have at least two impressive applications. First, they can be used as highly accurate clocks, comparable in stability to atomic clocks; secondly, a small subset of pulsars, millisecond X-ray pulsars, provide all the necessary ingredients for a passive galactic positioning system. This is known in astronautics as X-ray pulsar-based navigation (XNAV). XNAV is comparable to GPS, except that 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 (section 4). The paper starts by exposing the basics of pulsar navigation (section 2), continues with a critique of the rejection of the extraterrestrial hypothesis when pulsars were first discovered (section 3). The core section 4 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 (section 5). I discuss possible objections and potential benefits for humanity, whether the research program succeeds or not (section 6). Keywords: SETI, XNAV, space navigation, pulsars, global navigation satellite system, directed panspermia. Contents 1 Introduction..........................................................................................................2 2 Pulsar navigation..................................................................................................4 2.1 Normal and millisecond pulsars...........................................................................................4 2.2 Pulsar behavior....................................................................................................................7 2.3 Navigation with pulsars.......................................................................................................8 3 Dismissing the dismiss.......................................................................................13 3.1 Too much energy...............................................................................................................14 3.2 Not unique.........................................................................................................................14 3.3 Not a planet........................................................................................................................15 3.4 Not narrow-band................................................................................................................15 3.5 Natural model....................................................................................................................16 1 Pulsar Positioning System 4 The SETI-XNAV quest......................................................................................19 4.1 Galactic distribution...........................................................................................................20 4.2 Power distribution..............................................................................................................21 4.3 Population synthesis...........................................................................................................22 4.4 Evolutionary tracks............................................................................................................23 4.5 Synchronization.................................................................................................................24 4.6 Navigability near the speed of light...................................................................................25 4.7 Decoding galactic coordinates...........................................................................................25 4.8 Directed panspermia: navigation and propulsion...............................................................26 4.9 Information content............................................................................................................28 5 Pulsars as standards............................................................................................30 5.1 Frequency window standard..............................................................................................30 5.2 Pulse window standard......................................................................................................30 5.3 Pulsars and habitable stars alignment.................................................................................31 5.4 Timing and positioning standard........................................................................................32 5.5 Communication standard...................................................................................................33 6 Discussion..........................................................................................................34 6.1 SETI-XNAV, a modern bias?............................................................................................34 6.2 How (im)plausible is pulsar engineering?..........................................................................34 6.3 Who could have done it?....................................................................................................35 6.4 How could pulsar engineering work?.................................................................................36 6.5 Is SETI-XNAV new?.........................................................................................................37 6.6 What could the benefits be?...............................................................................................38 7 Conclusion.........................................................................................................39 8 Acknowledgements............................................................................................40 9 References..........................................................................................................41 10 Argumentative maps........................................................................................49 1 Introduction Navigation is a universal problem whenever one needs to go from point A to point B. Around Earth’s orbit, Global Navigation Satellite Systems (GNSSs) such as the American Global Positioning System (GPS) or the Russian GLObal NAvigation Satellite System (GLONASS) have revolutionized the way planes, boats, cars and pedestrians navigate. GPS did not appear overnight, but was the culminating outcome of ground-based radio navigation in the 1920s, gradually complemented by satellites. These satellites broadcast timing information that allow users to determine accurately not only their instantaneous position, but also their instantaneous velocity. GPS requires at least 24 satellites equipped with precise atomic clocks and algorithms calculating the position of satellites, which must correct for relativistic effects predicted by Einstein’s theory. GNSSs constitute a great achievement of modern science and engineering, and will continue to prove revolutionary for all kinds of location-based services in our Internet era. However useful on Earth, GNSSs are of little use for space missions in the solar system and in deep space. We could only dream of the equivalent of a GNSS on a galactic scale. Remarkably, though, it seems already to exist. Back in 1972, Carl Sagan, with Linda Sagan and Frank Drake, famously composed “A message from Earth”, to be placed on Pioneer 10 as a way of communicating our position in the galaxy to any extraterrestrials who happened upon the probe. The spacetime coordinates of Earth are encoded in the message, thanks to a reference to 14 pulsars and the galactic center (Sagan, Sagan, and Drake 1972, see figure 1). 2 Pulsar Positioning System Figure 1: The Pioneer 10 plaque. On the left, the position of the Sun is shown relative to 14 pulsars and the center of the galaxy However, the potential of radio pulsars for galactic positioning and navigation was fully explored only two years later by Downs (1974). At that time, Downs showed that spacecraft position could be determined with an error on the order of 1500 km in the solar system, and he pointed out ways to narrow down the error. Achieving an accuracy of even a thousand kilometers may seem largely sufficient on a galactic scale, but it is not enough for solar-system missions. For example, in order to land a spacecraft on a particular crater of a planet, higher accuracy is needed. The technique of pulsar-based navigation took a leap forward with the suggestion of Chester and Butman (1981) to use X-ray pulsars instead of radio pulsars. With their methodology, they showed that an accuracy of 150 km could be achieved. One important advantage of X-rays over radio waves is their short wavelength, which means they can be detected with small detectors that are easy to engineer into a spacecraft. One year after, the first millisecond pulsar (MSP) was discovered in the radio band (Backer et al. 1982)