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In the last half-century of space flight, our planet’s own orbits have become so littered with space junk, it gives pause to wonder if our orbital presence could be remotely observed by a nearby extraterrestrial civilization?
In a paper just submitted to The Astrophysical Journal, Hector Socas-Navarro, a senior scientist at Spain’s Instituto de Astrofisica de Canarias, turns this question on its head. He argues that our planet’s own plethora of geostationary satellites are not yet numerous enough to be visible to alien telescopes.
But Socas-Navarro told me that NASA’s forthcoming TESS (Transiting Exoplanet Survey Satellite) will likely gather photometric data of extrasolar earthlike systems that could reveal such artificial exobelts by the dimming they cause as they transit across the face of their parent star.
They are dubbed Clarke exobelts in referenc to a 1945 paper in which the science fiction icon Arthur C. Clarke advocated geostationary satellites as a means of implementing an earth-based global communications network. However, Socas-Navarro says that we are capable of detecting such an alien Clarke exobelt around a nearby Red dwarf star with our own current technology.
With current technology we could observe the Clarke exobelt of a civilization slightly more advanced than ours up to some 100 light-years away, says Socas-Navarro. A Clarke exobelt could perfectly well show up in TESS data, he says. That is, if there is one to be seen in the roughly 3000 exoplanets expected to be discovered by this mission.
Socas-Navarro writes in his paper that civilizations with a high density of devices and/or space junk in that region may leave a noticeable imprint on the light curve of the parent star. And because nature has no particular preference for this kind of orbit , he writes, its mere detection would be extremely suggestive of an artificial origin.
The best places to look would be around dim Red dwarf (M type) stars that were so close to their parent stars that the exoearths would inherently be gravitationally tidally-locked with their parent stars, so that only one side of the planet faces the star.
As for distinguishing such exobelts from a purely natural planetary ring?
A detection of a dense belt of objects at the distance of geostationary orbit would be a very strong evidence for the presence of extraterrestrial intelligences (E.T.I.), Socas-Navarro writes, especially considering that rings around habitable rocky planets are probably rather uncommon. He dubs such civilizations Moderately Advanced Civilizations since he says they would only be a couple of hundred years ahead of us --- a calculation that Socas-Navarro reaches by extrapolating what he terms the exponential growth of Earth’s own satellite industry.
But there’s a catch.
“All theoretical SETI (Search for Extraterrestrial Intelligence) papers are extremely speculative, since they depend on the nature of extraterrestrial intelligences (E.T.I.)s, of which we know nothing,” Alan Penny, an astronomer at the University of St. Andrews in the U.K., told me.
So the usual procedure is to say 'they are like us, but a bit more advanced' which is, in my view, extremely unlikely, says Penny. But this paper takes the last 10 years of geo-orbits, extrapolates their growth over the next 180 years to get a billion times more objects, he says. They would indeed be detectable, but that extrapolation, says Penny, seems like a bit of a stretch.
Yet Penny does concede that it's not beyond the realm of possibility that TESS might pick up data that could lend itself to being interpreted as evidence for alien exobelts.
As for whether our own satellites are detectable by E.T.s?
“They aren't, unless they had some very advanced observing technology,” said Socas-Navarro. “However, if we extrapolate our current rate of populating the Clarke belt, we would be detectable by our current technology by the year 2200.”
