Among many theories on locating aliens and gauging their technological advancements, a recent one about "space junk" has stirred a lot of buzz in the science community.
The Theory Of Space Junk
Numerous satellites have already been sent to outer space over the past few decades, and astrophysicist Hector Socas-Navarro of the Canary Islands Institute of Astrophysics in Spain believes that they might hold the key to finding an alien civilization on an exoplanet.
In a Feb. 21 paper published on arxiv.org, Socas-Navarro asserts that Earth's satellites — or space junk — leave a faint shadow circling the planet when it passes in front of the sun. The theory holds that alien civilizations might also send satellites around their planets, which would also leave a similar shadow when they pass in front of stars.
If this process occurs often enough, Socas-Navarro says that humans might be able to spot the non-transparent shadow around alien planets. Likewise, aliens should be able to locate the same shadow around Earth.
The current process for spotting aliens, known as transit method, involves watching the dip in a star's brightness when a planet passes in front of it. Thus, this theory fits within that process.
How The Theory Would Work
According to Socas-Navarro, humans would need to send about 10 billion to 1 trillion satellites into orbit before aliens could spot them. As of 2017, there are over 4,000 satellites orbiting the planet based on the Index of Objects Launched Into Outer Space maintained by the United Nations Office for Outer Space Affairs (UNOOSA).
If Socas-Navarro's theory is valid, it would take until the year 2200 before aliens could locate the Earth.
In addition to time, there is also another issue raised by other scientists about the space junk theory. Essentially, moons or rings orbiting exoplanets could be mistaken for space junk because they might be difficult to distinguish.
What The Satellites Could Tell Us
Apart from locating alien species in space, the proposed theory could also provide information about how technologically advanced the aliens are compared to human beings.
"Civilizations with a high density of devices and/or space junk in that region, but otherwise similar to ours in terms of space technology (our working definition of "moderately advanced"), may leave a noticeable imprint on the light curve of the parent star," Socas-Navarro wrote in his paper.
If aliens' satellites are more advanced than humans' satellites, then they are likely to be a more advanced civilization.