Is it the home of extraterrestrial life? For the first time astronomers have discovered a planet which satisfies the two main requirements: it is almost as large as Earth and orbits its host star in the habitable zone.

The dream destination of astronomy is blue : A planet that is as big as the earth , has abundant water and life allows – at least as we know it. For this purpose, it must orbit its host star in perfect distance . A bit too far , and the planet solidified in the cold. A bit too close, and it is grilled.

Although researchers have already discovered more than 100 exoplanets that are as tiny as the earth – but who were mostly in the barbecue area . While Others hover in the habitable zone, but are significantly larger than Earth. Now it’s the first time succeeded in finding an exoplanet that has both: the dimensions of the earth and a habitable distance from its host star .

Kepler – 186f belongs , as its name suggests, to an entire planetary system , in which he is the fifth and outermost planet at the same time . Its diameter is only ten percent larger than Earth , the researchers write about Elisha Quintana from the Seti Institute of the U.S. space agency Nasa in the journal “Science”. ” This is the first Earth-sized planet clearly that was found in the habitable zone of another star ,” said Quintana . The “Kepler” Space Telescope has spotted him when he has passed in front of its host star and its light has dimmed by a tiny amount .

Earth Twin Planet:”Significant discovery “

Until now had about 20 exoplanets known in habitable zones , according to an announcement from the Seti Institute. But all are significantly larger than the earth , so one can not be sure if they made ​​rock or – consist of gas – such as Saturn or Neptune. When Kepler – 186f things are different : With a diameter of less than 1.5 times the Earth it is highly unlikely , according to astronomer Thomas Barclay, that it was a gas planet.

That Kepler – 186f actually exists – and is not about an artifact in the telescope data – also appears virtually certain. The probability that Quintana’s team was mistaken , lying less than one percent , according to Hans -Jörg Deeg of the Instituto de Astrofísica de Canarias . Kepler 186 -f was ” quite clearly the most potentially habitable ” and also the most Earth-like planet under the known so far. ” His discovery is therefore very significant ,” said Deeg . ” And with him also the main objective of ‘ Kepler’ satellite has now been reached : the discovery of habitable Earth-like planets. ”

However, today’s telescopes do not yet permit direct observation of the atmosphere of the planet – why astronomers also can not tell if there really is life on Kepler – 186f . You’d have the chemical traces in the light spectrum of the gas envelope to prove – but what will be in a position only the instruments of the next generation , such as the one under construction James Webb Space Telescope.

But even with them it could be noisy astronomer Quintana be impossible to detect life on Kepler – 186f : Its host star is 490 light-years away from Earth and thus possibly too gloomy to facilitate more detailed studies .

Earth Twin Planet:Three times less solar radiation than on Earth

But one thing seems certain: Although Kepler – 186f may well harbor life , it would be for people not particularly pleasant destination. The reason for this is that the planet hovers in the outer part of the habitable zone . There he gets according to calculations by Quintana’s team from only about a third of the solar radiation that we are used to on Earth. Therefore, the atmosphere of carbon dioxide would have far more so that the greenhouse effect to prevent freezing of all water . ” When you land there, the mask should not decrease it ,” says Lisa Kaltenegger from the Max Planck Institute for Astronomy in Heidelberg , which was not involved in Quintana’s study. However, an increased CO2 concentration for non-human life should not be a problem.

Francesco Pepe , planetary scientist at the Astronomical Observatory of the University of Geneva , points to more unknown quantities . So far, only the diameter of the planet and its orbit are known. ” But how great are its mass and density , how dense is its atmosphere , and what is it ? Are there any water, even if the temperatures are low ? ” As long as these issues have not been clarified , can the question of the existence of life can not be answered .

The Seti Institute has Kepler – 186f since 2012 , when it already references to him were taken to the Allen Telescope Array to target and wanted by radio signals from an extraterrestrial civilization . But in a wide frequency range, the astronomers heard nothing but silence. Give up hope they still want not : To be received on Earth , the aliens would have to send its signal to a transmitter , the 10 – to 20 – times stronger than the giant radar telescope at Arecibo in Puerto Rico.

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