This Research, published in “Nature”, Using data collected by the European Space Agency (ESA) Gaia Space Telescope, which is mapping our Milky Way in unprecedented 3D.

When we are looking for exoplanets or planets orbiting other stars, one of the most popular methods is the transit method, in which the light of one of the stars drops slightly (probably close to 1%), which indicates that the planet has passed through the-or Transit-star.

However, this method requires the planet to be in our sight. It’s like someone holding a pea in front of a huge bulb; if you place it anywhere above or below the bulb, we won’t notice a slight drop in brightness.

The authors of the new study found that in the past 5,000 years, about 1,715 nearby stars can see the Earth through this transit method. Among them, 29 habitable planets around these stars may also be affected by humans. . Radio transmission began about 100 years ago. That is, if they know to look for radio signals.

Watch | Astronomers estimate the number of star systems that may have or can detect life on Earth:

But we know that there are potentially habitable planets around some stars: Ross 128; Tigaden Star; GJ 9066; TRAPPIST-1, K2-65; K2-155 and K2-240.

“So we have seven stars with planets, four of which are within 100 light years,” said Lisa Kaltenegger, an associate professor at Cornell University in Ithaca, New York, the lead author of the study.

“So who can see us passing by, and also, have they already received the radio waves that we started sending about 100 years ago? This is the whole question: Is everyone looking for radio waves? Does everyone develop radio technology? Nobody knows.”

The most interesting one is the TRAPPIST-1 system consisting of seven exoplanets, three of which are rocks and are located in a potentially habitable zone (water may be present on the planet’s surface).

However, Kaltenegger said, TRAPPIST-1 will not see us until 1600.

“So we have found it,” she said. “But their vantage point hasn’t reached this perfect place yet, and they haven’t seen us transit. So to some extent, we know something they haven’t known since 1600.”

Ross 128 is a red dwarf star about 11 light-years away, which means it is close enough to receive Earth’s broadcasts (radio signals travel at the speed of light), and it has a planet almost twice the size of Earth. If there is life there, they will see the earth transiting for more than 2,000 years. However, 900 years ago, they lost their view of the earth.

However, Tigaden Star, which is 12.5 light-years away from Earth, will be in a good position to receive Earth’s transmissions in 29 years.

Broadcast or not

When it comes to the search for alien life, the biggest question is whether we miss you Spread our existence into space: What if we remind a smart but not so benevolent species to pay attention to our existence?

However, despite the controversy, there is still a coordinated effort to find extraterrestrial intelligence, known as SETI, which is mainly composed of the SETI Institute and Breakthrough listening program.

“what [the authors] Seth Shostak, a senior astronomer at the SETI Institute who was not involved in the study, said: “What we are doing here is that they list all the things that can see the earth passing in front of the sun. A star system relatively close to us.” “So they gave SETI a bunch of targets.”

Although the signals have been sent from our radio transmissions to space, they are not directional, but what astronomers call “leaks.”

“If they have the kind of antenna we make, they won’t receive this kind of leakage radiation from the earth, right? Because… it was not aimed at them deliberately,” Shostak said.

only The directional signal was sent by the now-defunct Arecibo Telescope in 1974 In Puerto Rico. But it was sent to a star cluster M13 that is more than 21,000 light years away from us.

But so far, it has been very quiet. The closest we came to a potential signal was in 1977, often referred to as the “wow! signal”. It lasted for 72 seconds and then disappeared.Since then, people have been skeptical about this, and one of the papers claimed that it was due to Passing by the comet.

Astronomer Nick Cowan, an associate professor in the Department of Earth and Planetary Sciences at McGill University, was not involved in the study. He said there are many situations that can lead to silence.

“I mean there are many solutions, from the horrible, such as the moment you start leaking radio into space, no matter how long it takes for aliens to get here, they will come here and destroy us, to the real one. It’s frustrating,” he said. “Perhaps intelligent life is actually very rare. It appeared on Earth through a series of evolutionary fluke.”

This led to the Fermi Paradox, named after the physicist Enrico Fermi, who is said to have asked: “Where is everyone?” In 1950, decades before we discovered exoplanets, Have lunch with other scientists at Los Alamos National Observatory. The idea is that if there are so many stars, there should be millions or billions of planets, and the potential intelligent life we ??should be able to detect. But so far, we are greeted by silence.

But the search continues, and this recent study may help narrow down some targets.

“Now sometimes when I look up at the sky, I think,” Kaltenger said. “Have [about] There are 2,000 stars to see us now. I am an optimist, so I think the sky becomes more friendly because I imagine if life is there, it will wave there, you know? It’s like,’Hey, are you outside? ‘”