Welcome back to our Fermi Paradox series, where we take a look at possible resolutions to Enrico Fermi’s famous question, “Where Is Everybody?” Today, we examine the possibility that Earth hasn’t been visited by aliens because interstellar travel is not very practical!
In 1950, Italian-American physicist Enrico Fermi sat down to lunch with some of his colleagues at the Los Alamos National Laboratory, where he had worked five years prior as part of the Manhattan Project. According to various accounts, the conversation turned to aliens and the recent spate of UFOs. Into this, Fermi issued a statement that would go down in the annals of history: “Where is everybody?“
This became the basis of the Fermi Paradox, which refers to the disparity between high probability estimates for the existence of extraterrestrial intelligence (ETI) and the apparent lack of evidence. Since Fermi’s time, there have been several proposed resolutions to his question, which includes the Dark Forest Hypothesis, where extraterrestrial civilizations are deliberately avoiding contact.
When it comes to the search for extra-terrestrial intelligence (SETI) in the Universe, there is the complicated matter of what to be on the lookout for. Beyond the age-old question of whether or not intelligent life exists elsewhere in the Universe (statistically speaking, it is very likely that it does), there’s also the question of whether or not we would be able to recognize it if and when we saw it.
Given that humanity is only familiar with one form of civilization (our own), we tend to look for indications of technologies we know or which seem feasible. In a recent study, a researcher from the Instituto de Astrofísica de Canarias (IAC) proposed looking for large bands of satellites in distant star systems – a concept that was proposed by the late and great Arthur C. Clarke (known as a Clarke Belt).
This proposal is based in part on a paper written by Arthur C. Clarke in 1945 (titled “Peacetime Uses for V2“), in which he proposed sending “artificial satellites” into geostationary orbit around Earth to create a global communications network. At present, there are about 400 such satellites in the “Clarke Belt” – a region named in honor of him that is located 36,000 km above the Earth.
This network forms the backbone of modern telecommunications and in the future, many more satellites are expected to be deployed – which will form the backbone of the global internet. Given the practicality of satellites and the fact that humanity has come to rely on them so much, Socas-Navarro considers that a belt of artificial satellites could naturally be considered “technomarkers” (the analogues of “biomarkers”, which indicate the presence of life).
As Socas-Navarro explained to Universe Today via email:
“Essentially, a technomarker is anything that we could potentially observe which would reveal the presence of technology elsewhere in the Universe. It’s the ultimate clue to find intelligent life out there. Unfortunately, interstellar distances are so great that, with our current technology, we can only hope to detect very large objects or structures, something comparable to the size of a planet.”
In this respect, a Clarke Exobelt is not dissimilar from a Dyson Sphere or other forms of megastructures that have been proposed by scientists in the past. But unlike these theoretical structures, a Clarke Exobelt is entirely feasible using present-day technology.
“Other existing technomarkers are based on science fiction technology of which we know very little,” said Socas-Navarro. “We don’t know if such technologies are possible or if other alien species might be using them. The Clarke Exobelt, on the other hand, is a technomarker based on real, currently existing technology. We know we can make satellites and, if we make them, it’s reasonable to assume that other civilizations will make them too.”
According to Socas-Navarro, there is some “science fiction” when it comes to Clarke Exobelts that would actually be detectable using these instruments. As noted, humanity has about 400 operational satellites occupying Earth’s “Clarke Belt”. This is about one-third of the Earth’s existing satellites, whereas the rest are at an altitude of 2000 km (1200 mi) or less from the surface – the region known as Low Earth Orbit (LEO).
This essentially means that aliens would need to have billions more satellites within their Clarke Belt – accounting for roughly 0.01% of the belt area – in order for it to be detectable. As for humanity, we are not yet to the point where our own Belt would be detectable by an extra-terrestrial intelligence (ETI). However, this should not take long given that the number of satellites in orbit has been growing exponentially over the past 15 years.
Based on simulations conducted by Socas-Navarro, humanity will reach the threshold where its satellite band will be detectable by ETIs by 2200. Knowing that humanity will reach this threshold in the not-too-distant future makes the Clarke Belt a viable option for SETI. As Socas-Navarro explained:
“In this sense, the Clarke Exobelt is interesting because it’s the first technomarker that looks for currently existing technology. And it goes both ways too. Humanity’s Clarke Belt is probably too sparsely populated to be detectable from other stars right now (at least with technology like ours). But in the last decades we have been populating it at an exponential rate. If this trend were to continue, our Clarke Belt would be detectable from other stars by the year 2200. Do we want to be detectable? This is an interesting debate that humanity will have to resolve soon.
As for how these belts would be detected, that would come down to the most popular and effective means for finding exoplanets to date – the Transit Method (aka. Transit Photometry). For this method, astronomers monitor distant stars for periodic dips in brightness, which are indications of an exoplanet passing in front of the star. Using next-generation telescopes, astronomers may also be able to detect reflected light from a dense band of satellites in orbit.
“However, before we point our supertelescopes to a planet we need to identify good candidates,” said Socas-Navarro. “There are too many stars to check and we can’t go one by one. We need to rely on exoplanet search projects, such as the recently launched satellite TESS, to spot interesting candidates. Then we can do follow-up observations with supertelescopes to confirm or refute those candidates.”
While these space-telescopes would search for rocky planets that are located within the habitable zones of thousands of stars, next-generation telescopes could search for signs of Clarke Exobelts and other technomarkers that would be otherwise hard to spot. However, as Socas-Navarro indicated, astronomers could also find evidence of Exobands by sifting through existing data as well.
“In doing SETI, we have no idea what we are looking for because we don’t know what the aliens are doing,” he said. “So we have to investigate all the possibilities that we can think of. Looking for Clarke Exobelts is a new way of searching, it seems at least reasonably plausible and, most importantly, it’s free. We can look for signatures of Clarke Exobelts in currently existing missions that search for exoplanets, exorings or exomoons. We don’t need to build costly new telescopes or satellites. We simply need to keep our eyes open to see if we can spot the signatures presented in the simulation in the flow of data from all of those projects.”
Humanity has been actively searching for signs of extra-terrestrial intelligence for decades. To know that our technology and methods are becoming more refined, and that more sophisticated searches could begin within a decade, is certainly encouraging. Knowing that we won’t be visible to any ETIs that are out there for another two centuries, that’s also encouraging!
And be sure to check out this cool video by our friend, Jean Michael Godier, where he explains the concept of a Clarke Exobelt:
Welcome back to our ongoing series, “The Definitive Guide To Terraforming”! We continue with a look at the Moon, discussing how it could one day be made suitable for human habitation.
Ever since the beginning of the Space Age, scientists and futurists have explored the idea of transforming other worlds to meet human needs. Known as terraforming, this process calls for the use of environmental engineering techniques to alter a planet or moon’s temperature, atmosphere, topography or ecology (or all of the above) in order to make it more “Earth-like”. As Earth’s closest celestial body, the Moon has long been considered a potential site.
All told, colonizing and/or terraforming the Moon would be comparatively easy compared to other bodies. Due to its proximity, the time it would take to transport people and equipment to and from the surface would be significantly reduced, as would the costs of doing so. In addition, it’s proximity means that extracted resources and products manufactured on the Moon could be shuttled to Earth in much less time, and a tourist industry would also be feasible.
In our previous episode, we introduced Arthur C. Clarke, the amazing man and science fiction writer. Today we’ll be discussing his legacy and ideas on space exploration. You’ll be amazed to hear how many of the ideas we take for granted were invented or just accurately predicted by Arthur C. Clarke. Continue reading “Astronomy Cast Ep. 331: Arthur C. Clarke’s Technologies”
Arthur C. Clarke was one of the greatest science fiction writers of all time. He defined the genre, and revolutionized our ideas about what it will take to become a true space faring civilization. In the first of our two part series on Arthur C. Clarke, we examine the man’s life and his books. Continue reading “Astronomy Cast Ep. 330: Arthur C. Clarke”