Are there extraterrestrial spaceships?

A boulder that always stays close to the earth : Is Kamo'oalewa an alien watch post?

It would be the greatest discovery humans have ever made: We are not alone in the cosmos! So far, however, radio antennas have only picked up noise when searching for signals from extraterrestrial intelligence. And to date no spaceship from a distant solar system has appeared in the sky of the earth. Why not?

In our home galaxy, the Milky Way, around 200 billion other stars shine in addition to the sun. Many of them, perhaps most of them, are orbited by planets. The first of these “exoplanets” was discovered in 1995 by the two Swiss astronomers Michel Mayor and Didier Queloz, for which they will be awarded the Nobel Prize in Physics on December 10th. In the meantime, more than 4,000 other exoplanets have been found. Most of them do not offer good conditions for life, but some do.

Scientists from the University of Puerto Rico keep a list of the exoplanets known to date on which life could in principle be possible: They are of a similar size and mass to the Earth and therefore probably have a solid surface. And they are at the right distance from their respective star so that it is neither too hot nor too cold on them.

The researchers have already found 16 such planets within a small radius of 50 light years. A simple extrapolation to the entire Milky Way gives an idea of ​​how many potentially habitable planets there could be in the vastness of our home galaxy: at least 30 million. But that is where our knowledge ends.

"Where are they all then"

Everything that follows is only speculation with probabilities: If a similar development had taken place on every thousandth of the basically life-friendly planets as on Earth, then, yes, the Milky Way would be teeming with intelligent living beings.

Most of them would have acquired the ability to do space travel a long time ago, rather than just a few decades ago like humanity. And probably not all, but some of them, would have long since set out on interstellar journeys through the Milky Way - out of curiosity, in search of raw materials, out of the urge to expand, or for whatever motive.

But then the aliens should have appeared in our solar system long ago. As early as 1950, the Italian Nobel Prize winner Enrico Fermi posed the question that was to become famous as the "Fermi Paradox": "Where is everybody - where are they all?"

One of many possible answers is: You have long been near us. It doesn't necessarily have to be the aliens themselves. To explore the vast spaces of the Milky Way, they probably use space probes that, controlled by artificial intelligence, could manage flight times of millions of years.

Sooner or later they would have to have visited our solar system as well; its third planet should have quickly caught your attention with its special atmosphere and seas. And if the interplanetary scouts had happened by chance in our times, the radio waves from countless radio and television stations would have quickly betrayed our existence to them anyway.

Asteroids as ideal observation posts

So far, however, apparently no aircraft from distant worlds has landed on earth. Perhaps the aliens will first observe the blue planet from a safe distance and report back home what is happening on it. In the “Astronomical Journal” the physicist James Benford recently described where the alien probes could have pointed their antennas and sensors at us: They could be standing on asteroids. Most of these minor planets curve far out in the asteroid belt between Mars and Jupiter. So observing the earth from them would not be particularly intelligent. However, some of the boulders circle the sun on orbits with good views of the blue planet.

Of all the asteroids known to date in the solar system, "Kamo'oalewa" would be best suited as a spy asteroid for extraterrestrials. The 40 to 100 meter large boulder was only discovered on April 27, 2016 with the Pan-STARRS 1 telescope operated in Hawaii.

The Hawaiian name of the asteroid points to its peculiar movement: on its orbit around the sun, the asteroid first hurries ahead of the earth, then slows down, follows it for a while, becomes faster again, overtakes the earth again - and so on .

As mysterious as this dance of the asteroid around the earth may appear, it simply obeys the laws of celestial mechanics: Kamo'oalewa flies in about 366 days on a very similar elliptical orbit around the sun as the earth. However, one half of the asteroid's orbit is a little closer to the sun than the orbit of the earth; on this section of the orbit the asteroid flies a little faster than the earth and therefore overtakes it on the inner orbit.

About a quarter of a year later, the asteroid then reaches the section of its elliptical orbit in which it is further away from the sun than the earth. This makes him slower than her and is now overtaken by her in turn. Even though the earth's gravitational pull is too weak to bind the asteroid directly to itself, it still remains close to us.

A probe is scheduled to visit Kamo'oalewa in 2022

Even during the mutual overtaking maneuvers, Kamo'oalewa is about 40 times further away from us than the moon. However, this distance would not be a problem for sophisticated observation technology. A probe installed on the asteroid by an extraterrestrial civilization could easily track the behavior of mankind and its development over long periods of time - and this from constantly changing perspectives: While the asteroid overtakes the earth on the inner orbit, you can see the from him day side of the earth shining in sunlight; on the other hand, while the earth overtakes him, the sensors of the probe from the outer orbit could target the night half of the earth facing away from the sun.

There is no doubt that if space were actually teeming with highly developed civilizations, we would have to take this scenario seriously. Perhaps the aliens are just waiting for humanity to reach a certain level of civilization before they reveal themselves and welcome us to the club of sensible, peaceful galactic civilizations.

But how likely is this scenario in reality? We will soon be able to assess it a little better: The Chinese space agency plans to send a space probe to Kamo'oalewa in 2022. The official task of the probe is by no means to search for any signs of extraterrestrial presence on it. Rather, among other things, it should take soil samples and bring them back to earth. The researchers hope that the study of the asteroid rock will provide information about its formation in the early days of the history of the solar system. And of course cameras on board the probe will also provide images of Kamo'oalewa.

But what if they should show the asteroid as a barren boulder with no trace of an alien civilization on it? From this negative "alien archeology" an important finding can be derived, writes Benford to the Tagesspiegel: "If no foreign probe has come near us in the past millions of years, the probability that there is even extraterrestrial intelligent life decreases". And that would raise new questions: What has prevented the development of intelligent civilizations on the appropriate planets - maybe even on all of them, with Earth as the only exception?

Aren't the aliens reporting because every higher civilization out there has been self-extinguishing so far?

There is another - disturbing - possibility: Perhaps living things have already existed on many of the planets in the Milky Way whose biological evolution eventually produced a highly developed civilization. But if we have not heard or seen anything from them to this day, it could be because they all, or almost all, have long since died out again.

Some researchers have a bad suspicion: Perhaps every, or almost every extraterrestrial civilization has ushered in its own downfall with the entry into its technical age. Then of course we would not be able to find anything on Kamo'oalewa that would indicate a visit by extraterrestrials.

If, on the other hand, we should actually come across any traces of extraterrestrial origin - even if it were just a probe that has been dead for millions of years - we could look far more optimistically into the future. Because then at least one alien civilization on a distant planet would have apparently achieved what the mathematician and philosopher Bertrand Russell classified as very difficult in our case as early as 1946: persuading humanity to consent to its own survival.

Whatever the outcome of the Chinese mission to Kamo'oalewa: It will definitely be more informative than the number 42 with which a computer in Douglas Adam's novel “The Hitchhiker's Guide to the Galaxy” raises the question of “life, the universe and all the rest ”answered.

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