Both worlds are similar to Earth, orbiting sun-like stars and located in the same constellation at about the same distance from us.
This is the Green Bank radio telescope, located in the eastern United States in what is called the radio silence zone, that is, in an area where very little use is made of anything that emits radio waves.
If, for example, the emergency services need to notify the population about something, they have to alert the observatory. That's where they listen to the space. Green Bank is one of the main tools of the SETI project: Search for Extraterrestrial Intelligence. The fully rotatable 100-meter dish can be pointed at any point in the sky, or more precisely, at the part of the celestial sphere that is above it.
A group of SETI scientists received a six-hour observing window several years ago on March 25, 2018. The experts decided during that time to listen for exoplanets that would pass over the disks of their stars at that moment, this is called a transit. They counted as many as hundreds of such planets, but from them they had to choose only a few that are closer to us and to each other in the sky. Recall that today officially confirmed more than five thousand exoplanets, many of them have a year, that is, the period of rotation around the star is only a few days. That is, they transit through the disks of their parent stars every few days.
In this case, we stopped at the 12 planets in the constellation of the Swan. By the way, there nearby is also the famous star Tabby (sometimes it is called the Boyajian star after the name of its discoverer), which has long been worrying with absolutely mysterious irregular transits of unknown things in front of it.
The selected planets are either about the size of Earth or one and a half Earths, and one is 12 times the size of Earth, that is, even larger than Jupiter. And it really is a gas giant, it has no solid surface, but, on the other hand, it may well have solid satellites, like our Jupiter. These exoplanets follow the disk of their star (some - forty minutes, others - almost four hours), but scientists have observed each transit for only a few minutes.
What the scientists want to hear: First, they need a radio frequency of about 1420 megahertz. The fact is that hydrogen, the most abundant element in the Universe, "broadcasts" at this frequency. In addition, at this frequency, the background general galactic radio noise is almost inaudible. Therefore, astrophysicists reasoned that it would be most logical for a hypothetical extraterrestrial civilization to choose this frequency. Secondly, it is much easier to catch the signal of an extraterrestrial civilization if it is narrowband, again, easily distinguishable from the general background.
Twelve planets were listening in the 1100 to 1900 megahertz range. Interestingly, the calculation was that if there is someone intelligent there, they know about us and purposefully send a signal to us. So, from their point of view, it is best to signal when their planet in our telescopes turns out to be clearly in the middle of the disk of the star, because at this moment it looks exactly at the Earth. And thus astrophysicists underline that if we the meaningful signal from them will catch, they have the transmitter absolutely in 60 times more powerful that that stood on a well-known telescope Arecibo in Puerto Rico. Recall that earthlings sent messages to their brothers in intelligence, including with Arecibo and from the telescope RT-70 in Evpatoria.
In the end, the most similar to what was needed was heard from two planets. One of them, Kepler-1332 b, is as massive as two and a half Earths, and the other, Kepler-842 b, is three times more massive than our planet. Both are about 1,700 light-years away. Both are near stars slightly smaller than the Sun. One star is slightly hotter than our sun, the other is cooler and dimmer, an orange dwarf. Actually, to be honest, it's hard to imagine how heat-resistant and refractory intelligent life must be there: these worlds are several times closer to their stars than Mercury is to the Sun.
And yet the signals from them came in just about the right frequency: 1749 megahertz and 1040-1438 megahertz, respectively. True, they were quite broadband, but perhaps the more surprising thing is that we caught them. In addition, scientists say that it is still necessary to make allowance for the fact that others may reason and develop technology in a different way. And the most curious thing: both signals were received just when the planets were at the very center of the star's disk.