If aliens have visited the solar system, here’s how to find clues
Have intelligent aliens ever visited the solar system? It’s not a ridiculous question. At least the solar system has been around for over 4 billion years, and if intelligent life arose in our galaxy, it may have reached the level of technology needed to study other systems, including our own.
In a new paper, scientists outline how we can look for clues visitors may have left behind.
There are several main ways to look outside for information Earth. The first approach is to look for signs of life, whether intelligent or not. This is by far the most common method in astronomyand is usually geared towards other star systems – for example in search of life-generating chemicals in the atmospheres of other worlds. But the Search for extraterrestrial life also considers locations within the solar system, such as the surface of Mars and the hydrocarbon-rich atmosphere of Saturn’s moon titanium.
Another approach is to specifically search for intelligent life, since intelligent aliens are believed to be able to announce their presence far more easily than a microbe. For example, we can look for communicative extraterrestrials broadcasting their existence in radio or optical wavelengths. Looking for artificial radio signals is the alpha and omega of the search for extraterrestrial intelligence (SETI).
Related: Why are we still looking for intelligent extraterrestrial life?
But intelligent aliens can also drop other clues. If they are able to build so-called megastructures, such as Dyson swarms, then we can recognize these megastructures when searching in other systems. For example, sufficiently large structures around a star would change the light we see and could be a sign of intelligent activity.
So far, every search for extraterrestrial life has come to nothing. But there is another avenue that is still relatively unexplored: the Search for alien artifacts (SETA). The idea behind this approach is that once aliens are advanced enough, they will want to explore the galaxy either on their own or with robotic spaceships. In the approximately 4.5 billion year history of the solar system, these extraterrestrials would have had plenty of time to drop by our neighborhood and perhaps leave their tracks.
The rest
Unlike SETI, SETA allows astronomers to delve deep into the past. You don’t have to hope to pick up a radio signal from a civilization active at the same time as our listening. In fact, multiple civilizations may have come and gone over time galaxyeach leaves something in our solar system before it fades away (or moves on to something more interesting).
In a new article published in the Preprint database arXiv, astronomers proposed a strategy to use existing telescopes, surveys, and planetary probes to look for signs of past extraterrestrial visits. They discuss three categories of remains that we might discover.
The first category is normal surface artifacts – dead and leftover spacecraft, probes and even just junk. In the comparatively short time that mankind has explored the solar system, we have dotted the moon and mars with dozens of defunct spacecraft and random pieces of junk, so it’s not implausible to surmise that a visiting extraterrestrial civilization would do the same. Since many surfaces in the solar system do not experience weathering or volcanism, an artifact left there could be visible for billions of years.
In addition to surface artifacts, spacecraft can hang around in interplanetary space – a category commonly known as “lurkers”. They could be waiting in a stable gravitational Lagrange point or orbiting a distant moon. They could be active, monitoring and recording interesting things happening in the solar system, or they could be long dead and little different from one asteroid or comet.
Eventually, we might encounter interstellar artifacts that are never meant to stay in a star system, but rather wander aimlessly through the galaxy, traipsing from one system to another. We already have several means to discover this type of artifacts such as: B. Broad astronomical survey telescopes and planetary missions.
signs of damage
Speaking of travel, we could potentially find evidence of interstellar and interplanetary adventures with existing research. For example, every interstellar spacecraft worth the money needs a propulsion method. And because extraterrestrials also have to obey Newton’s Laws, there has to be some kind of exhaust to power the spaceship. The faster we want the vehicle to go, the more powerful its exhaust needs to be, potentially making it visible to the public James Webb Space Telescope or the Chandra X-ray Observatory.
Interstellar travel could also play a role Laser drive via light sail, which could be detectable. Or we could find evidence from more subtle clues, like gravitational anomalies — orbits of small objects that don’t make sense because they may have been disturbed by a passing spacecraft.
Finally, we can look in the solar system for signs of past interference, and not just passive observation. When aliens open an opencast mine mercury, for example, we could still see it today. Or if heavy equipment is still active, there would be some waste heat associated with it, contrasting with the radiation emitted from the surface of a planet or moon. Finally, we may be able to find geochemical anomalies – the result of tinkering with chemical processes on a world (or just plain pollution).
The authors highlighted how we could use current and planned Solar System observatories and probes to search for these artifacts without having to change their mission parameters. If we are already scanning planetary surfaces and imaging large parts of the solar system, we can piggyback on these campaigns to look for evidence of extraterrestrial life.
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