Berlin. For almost 46 years, “Voyager 1” has been zooming through space, past Jupiter, Saturn, to the edge of our solar system. No probe of mankind reaches deeper into space than this space probe. Also on board: music by Mozart and Louis Armstrong, greetings in Arabic and Mandarin. However, they have not been heard – at least as far as we know.
With probes, manned spaceships and radars the size of soccer fields, experts are scouring space for extraterrestrial life – so far in vain. Nevertheless, the majority of the experts stick with it: We are not alone, the cosmos is too big for that. In addition, there are significantly more planets and thus possible habitats in the universe than previously assumed. New such exoplanets are discovered almost every day.
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There are many exoplanets
“Even in the 1970s and 1980s, most experts agreed that exoplanets are rare,” says space expert and author Eugen Reichl. An exoplanet is a celestial body outside our solar system that orbits a star such as our sun. Today, however, around 5500 such planets have already been confirmed. And: “We now assume that the vast majority of the approximately 100 billion suns in our home galaxy are accompanied by planets,” says Reichl. If you add other galaxies from the vastness of the universe, the number of possible exoplanets increases immeasurably.
However, only a fraction of it is likely to be suitable as a habitat. A central factor: the distance to the respective sun. “In our solar system there are ‘two and a half’ planets in this habitable zone,” says Reichl. The earth is optimally located, Mars on the outer edge and Venus rather too close to the sun – their climate has also gotten out of control due to a greenhouse effect. The focus is also on icy moons of the outer gas planets Saturn and Jupiter: Reichl says life could be hidden under their kilometer-thick layers of ice, like in our deep sea.
Are there aliens – and are they here yet?
Are we really alone in the universe? Hardly anyone in science is convinced of this anymore: It is much more likely that mankind is just one of many intelligent civilizations. Some researchers even assume that extraterrestrials were already in our solar system. But there is no evidence.
Earthly life as a benchmark
All of this is based on the assumption that extraterrestrial life functions in a similar way to that here on earth – that it is an organism with a metabolism that needs water, among other things. Findings of methane, for example, are interpreted as successes because it can be a remnant of biological processes. Researchers speak of a so-called biosignature.
Venus in particular, as the “twin” of Earth, is repeatedly suspected of harboring extraterrestrial life. In the meantime, however, it is clear: the cloud cover of Venus does not consist of water, but of sulphur. And with over 450 degrees Celsius, the temperatures on the surface are rather unfavorable. So if there was life, it must have been a long time ago.
Search methods are still too rough
And even outside of our solar system, the search remains tricky. “If there were a solar system like ours in the Milky Way, it would currently slip through our fingers,” says Louise Nielsen, who researches exoplanets at the European Southern Observatory (ESO) in Garching. The methods that experts use to search for planets are not yet fine enough, says Nielsen. However, there are plenty of missions that are working on exactly that. “We can expect a breakthrough here in the next five to ten years,” says Nielsen.
Finding similar solar systems is important because most of the stars in the Milky Way are so-called red dwarfs. They are also orbited by planets made of rock and water, which would be an important condition for life. However, red dwarfs regularly bombard their planets with X-rays – this leads to a rather uncomfortable environment for living beings.
Researcher considers planets like Earth to be rare
“Actually, higher life requires a star like our sun,” says Ulrich Walter, ex-astronaut and professor of space technology at the Technical University of Munich. A planet in this solar system must also be large enough to hold an Earth’s atmosphere. In addition, it depends on the right moon and – linked to this – on a constant climate. “For at least two to three billion years,” says Walter.
So several factors come together. Walter therefore believes that planets like our Earth are very rare in the Milky Way. Maybe even once.
Despite this, experts assume that life does exist – although perhaps not in the form we know from “ET” or “Star Trek”. “The first find is probably somewhere between a virus and a bacterium,” says Eugen Reichl. The more complex the life form, the rarer.
Contact with aliens unlikely
And even if there were aliens, it is unlikely that we would come into contact with them because of the enormous distances. “Assuming there are ten civilizations in our Milky Way, they would be about 30,000 to 40,000 light years apart,” says Ulrich Walter. This means that a light signal would take at least 30,000 years to get there – and that’s how long we would have to wait for an answer. “I don’t think communication can work that way.”
Walter, who flew into space in 1993, thinks the chances of direct contact are particularly low. The area of the cosmos explored by humans is microscopic in relation to the Milky Way. “Less than a grain of sand in the Mariana Trench,” says Walter. “Practically zero.” This also applies to “Voyager 1”, which has been zooming through space for almost 46 years.
distances too great
Walter uses an example to calculate how unbridgeable the distances would be: Even if a civilization were only ten light-years away, which is considered unlikely, and it could travel at a hundredth of the speed of light – unthinkable with conventional drives – it would be on the road for around a thousand years. “The logical consequence of all this is that there can be no extraterrestrials on earth,” says Walter.
The search for extraterrestrials has electrified society and science for decades. The debate gained momentum around 1961 as a result of a conference in Green Bank, West Virginia. There, the astronomer Frank Drake created the equation named after him, which is supposed to determine the number of civilizations in the Milky Way. Many of its variables are still unknown today, such as the number of planets. Nevertheless, the equation stimulated the imagination – and is still much discussed today.
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Seti Institute listens for extraterrestrial radio waves
Another key player: Carl Sagan. He was responsible for the greetings that were sent into space on the “Voyager” probes in the 1970s. And in 1982, the astronomer, together with 70 scientists, published an appeal in the magazine “Science”. “We urge the organization of a coordinated, worldwide and systematic search for extraterrestrial intelligence,” Sagan wrote.
The SETI Institute was founded a little later. SETI stands for Search for Extra-Terrestrial Intelligence. To this day, the facility in space listens for radio waves from other civilizations.
“Discovery” of America did not end well for Native Americans
Today, many experts are more skeptical about a meeting. If, contrary to expectations, a civilization manages to come to earth, according to Ulrich Walter, it will only take on the hardships for one reason: the search for a new home planet. “In this respect, I’m glad it hasn’t come to that yet.”
The astrophysicist Stephen Hawking remained similarly skeptical. “If extraterrestrials ever visit us, I think the outcome will be the same as when Christopher Columbus landed in America, which didn’t end very well for the natives,” he said in the documentary Into The Universe with Stephen Hawking.
Will researchers ever find remains of extraterrestrial civilization?
Sociology also deals with the effects of a meeting. “For a long time, scientists underestimated the cultural effects of contact with an extraterrestrial civilization,” says Michael Schetsche from the University of Freiburg. He specializes in exo-sociology, which examines the relationship between humans and extraterrestrials. Although direct contact is unlikely, it could have a “culturally devastating” effect.
In any case, Schetsche considers it more likely that we will find an artifact, a remnant of other civilizations: because the time factor does not play a role here. “So we could still find the remains of an extraterrestrial expedition that explored our solar system near Earth long before mankind even existed,” says Schetsche. “We’d just have to look for it.”
Of course, it would also be possible the other way around – that our remains will be found long after humanity has ceased to exist. For example, the “Voyager 1” – with music by Mozart and Armstrong. And greetings in Arabic and Mandarin.