Exoplanets photo
An alien planet ringed with satellites transits in front of its sun.
A band of satellites orbits a planet crossing in front of a star. This could be Earth in a few centuries. Or an alien civilization today. Courtesy of Hector Socas-Navarro

The Earth is expanding, satellite by satellite, every rocket launch carrying a piece of the planet’s crust into orbit. Should this incidental geoengineering venture continue, it will reshape our planet’s profile as seen across even interstellar distances—giving our smooth sphere a noticeable bulge.

If we’re puffing up our planet, other civilizations could be doing the same to theirs, producing a ring of satellites that we might be able to spot with telescopes we have today. That’s according to Hector Socas-Navarro, an astrophysicist at the Instituto de Astrofísica de Canarias in Spain, who gave a talk on the topic at NASA’s Technosignatures Workshop in Houston last week. Scientists have long speculated that fantastical sun-sized structures might betray the presence of technological aliens, but while a mega-solar panel blocking a distant star is theoretically easy to spot, such notions remain squarely in the realm of science fiction. Thought experiments like Socas-Navarro’s, however, show that now, equipped with better telescopes than their predecessors, researchers are taking searches for planet-level changes more seriously.

Socas-Navarro realized that one planet-scale project in particular should have a specific and visible effect. Imagine a world something like Earth but a few hundred years ahead, technologically speaking. In this world, the alien military has launched GPS satellites to help with navigation. Alien NASA and alien Google have also launched countless weather and mapping satellites to deliver real-time feeds of the entire planet. Many of these satellites sit in special spots, geosynchronous and geostationary orbits, where they move in lockstep with their planet, letting them monitor the same area all the time. Fill in those special orbits and you get a thin cylinder ringing the planet, one that, when it passes between its star and an observer (like us), casts a slightly different shadow out into space than the naked planet would alone. When that shadow sweeps by the Earth, planet-hunting satellites like the aging Kepler and newly functional TESS could witness the alien star dimming in a specific way.

Exoplanets photo

Socas-Navarro published preliminary simulations in The Astrophysical Journal in March showing what that dimming would look like to modern telescopes if we were to watch such an Earthlike planet about ten light-years away. A satellite ring as thin as ours would be too sparse to see, he concluded, but Kepler could spot one about a billion times denser—a radical, but not impossible change that we could pull off in 200 years if launches continue to grow at current rates.

Plenty of people are already studying these stellar flickers, searching for something similar: a planet with natural rings. “It makes for a tricky transit, a tricky shadow,” says Masataka Aizawa, a graduate student at the University of Tokyo who found one possible Saturn cousin in 2017. He agrees that the dimming from a dense satellite belt should look unique. Natural rings spread out equatorially like a record while geosynchronous orbits form a north to south tin-can shape with vanishingly thin walls (ours currently measures just 450 feet thick), and the two geometries should cast two distinct shadows. But he still considers the paper’s suggestion, which he calls “science fictional,” a long shot. “I saw almost all of the [dimming] curves in the Kepler data, and there is no such evidence in my study,” he said.

Whether satellite-loving aliens are out there or not, running more detailed simulations of how the dimming patterns of moons differ from those of rings and satellite swarms helps all exoplanet researchers, Socas-Navarro points out. “We have to make sure we don’t misinterpret something as interesting as aliens, that we don’t mistake [them] with a natural ring or a natural moon,” he says. “If you look deeply they are different.”

While the technosignatures workshop focused on listening, not talking, Socas-Navarro’s ideas also suggest a sweeping conclusion about the nature of the first contact between two species. For decades our radio receivers and telescopes have restricted our potential pen pals to what he colorfully dubs “big brothers”—civilizations with unthinkably advanced technology. These species would be capable of engineering feats such as literally moving stars around, but recent surveys for traces of “astroengineering” have come up short.

As humanity’s capacity to observe advances, the type of civilization we can detect grows closer in nature to our own. Socas-Navarro’s satellite ring is the mark of a moderately advanced civilization just centuries ahead of us, rather than millennia. And he’s not the only one thinking along those lines. Others have proposed looking for orbital mirrors that could warm or cool a planet, something we humans have recently discussed as a potential solution to our own changing climate.

Any thought experiment about alien civilizations has to start with the only civilization we know, and compared with the technologists of the 1960s, climate change has burdened modern researchers with a more nuanced understanding of how technology can destabilize a civilization. “We are facing global problems that we didn’t have before, like global warming,” Socas-Navarro says, “so there is motivation to start global scale projects.” Based on our current experience, it’s not a big jump to wonder whether other civilizations, if they exist, have faced similar challenges—and found technological solutions.

Over the last seventy years, our machines have developed from being able to observe a civilization that controls stars to one that controls merely its own planet. And in the not too distant future, Socas-Navarro predicts, the synthesis of next-gen telescopes with the developing field of astrobiology will bring us to another tipping point. “We are not far from the transition,” he told an interdisciplinary audience of astronomers, archeologists, and anthropologists in Houston on Thursday. “In the next few decades we will be able to see ourselves at interstellar distances, and then we will become big brothers.”

Since little brothers can most easily detect big brothers, the hypothesis suggests that contact will tend to occur between species with a sizeable technology gap. Such contact between human civilizations has not turned out well for the little brother historically, but Socas-Navarro sees one potential reason for optimism.

Based on humanity’s experience with rapid development, researchers speculate that a “sustainability filter” may stop more violent species from reaching technological maturity. Expansionists that fail to check their aggressive impulses may quickly overrun their environment, triggering a technology-resetting crash, or even outright extinction.

Our current struggle to find a balance with our ecosystem suggests we could be facing just such a filter. Climate change threatens to render swaths of the planet uninhabitable by the end of the century, a blow that would derail economic and technological development. Clearing this hurdle, and finding a way for seven to ten billion people to live comfortably yet sustainably, will require that we take an active hand in managing the planet’s climate and resources. Should we reach that point, we’d be able to keep launching satellites and engage in other planet-shaping activities that could be seen from afar. By the same logic, other highly visible civilizations are also more likely to be active curators of their planets.

“They will implement changes to their planet just as a gardener will change his garden,” Socas-Navarro says.

In such a universe, most instances of first contact would be between mature gardeners and those grappling with their own unruly gardens. The likely outcome of such contact, one hopes, would be a gardening lesson.