Space explorers have turned, for a moment at least, from the search for hypotheses about the possibilities of an extraterrestrial civilization. This time they have asked themselves a different question – if alien civilizations have appeared somewhere in space, can they be aware of the existence of Earthlings?

We Earthlings have a catalogue of 1,715 star systems in our cosmic neighbourhood, from which a possible extraterrestrial civilization could observe the existence of our planet in the last 5,000 years. Such an observation is possible – at least according to terrestrial scientists – when the planet appears in the background of a star.

At first, scientists made a list of 1,715 star systems, positioned in such a way that their observers could see the Earth in the last 5,000 years of seeing it pass in front of the sun’s surface.

Of this list, 46 star systems are close enough for their planets to capture a clear sign that our Earth is inhabited. They can be radio or television signals sent out in the last hundred years.

The researchers estimate that 29 planets in those 46 systems are potentially inhabited, which means that their structure and climate do not preclude life on them. If any of those planets are inhabited by intelligent civilizations, their inhabitants could intercept some signals from Earth. Perhaps even infer that there are intelligent life forms on our planet.

There were 2,034 stars within 100 parsecs, or 326 light-years, that would be able to see the Earth in a period of 5,000 years and 5,000 years from now.

They include, for example, Ross 128, the red dwarf in the constellation Virgo, 11 light-years away, which is twice the size of Earth. Our planet was visible from there for 2,000 years, but this contact broke off 900 years ago. However, possible inhabitants of one of the two planets orbiting Teegarden’s Star 12.5 light-years from Earth will be able to intercept our television signal in 29 years.

Authors of the new research, published in Nature study, are List Kaltenegger, director of the Carl Sagan Institute at Cornell University in New York, and the astrophysicist at the American Museum of Natural History, Jackie Faherty.

Scientists emphasise that the transit method is only one of the methods of detecting new planets. This year, for example, the James Webb space telescope is to be launched, which will search for life on extrasolar planets by analysing the composition of their atmosphere.