People have always wondered if there is life on other planets. Given how many star systems there are, most people do not doubt the existence of life on other planets. While trying to find evidence for the existence of life on other planets, perhaps the inhabitants of other planets have already noted the existence of life on planet Earth. A new study has found that up to 1,715 star systems could learn about the existence of life on Earth in the last 5,000 years.

What did the study find?

If there was an advanced civilization in any of these systems, it could see the evolution of life on our planet. Out of those star systems, 313 exited the Earth transit zone (or ETZ), where they had a direct view of the Earth for thousands of years.

The study is based on specific data. Researchers used the Gaia database – a catalog of public data produced by the European Space Agency, which has data on more than a billion stars in the Milky Way. Lisa Kaltenegger (Associate Professor in Astronomy at Cornell) and Jaqueline Faherty (an astrophysicist at the American Museum of Natural History) researched what other civilizations might know about us.

A total of 1,715 star systems are in a position to monitor human evolution over the past 5,000 years. The 75 star systems are close enough to receive man-made radio waves.

How to find out the existence of a planet?

Many exoplanets can be discovered by mere observation. As the planet passes between the observer and the star, it creates a small dimming on the star. Thanks to this, its existence can be detected and it is also possible to estimate the size of the planet. As a planet orbits a star, some of the light is filtered through the atmosphere, and the planet’s atmosphere can be determined from that. If someone watched our planet, they could conclude from mere observation that it was habitable.

“The discussion on whether or not we should send out an active signal or try to hide our presence is ongoing,” the study notes. “However, our biosphere has modified our planet’s atmosphere for billions of years, something that we hope to find on other Earth-like planets soon. Thus, observing Earth as a transiting planet could have classified it as a living world since the Great Oxidation Event, for a billion years already.”

There can be many extraterrestrial observers

SETI (Search for Extra-Terrestrial Intelligence) is a project dealing with the search for extraterrestrial civilization by intercepting radio communications. While this project seeks only civilizations that can communicate with us at a distance, there may be hundreds of civilizations that know about us and only watch us quietly.

Research into other worlds can better explain how extraterrestrial civilizations can see our planet.