The most productive way for astronomers to search for planets is to use the transit method, worlds that cross or transit in front of their stars. Starting from this premise, the researchers wondered how many nearby stars and planets could have seen the Earth and, with it, have detected life on our planet. Now, the team of researchers from the Carl Sagan Institute of Cornell University (USA) has produced a complete catalog of the 2,034 stars from which aliens could be observing us.
Are you watching us?
If some extraterrestrial is looking for another type of intelligent life similar to his, they could use the same ‘trick’ that we use.
“From the point of view of the exoplanets, we are the aliens. We wanted to know which stars have the right point of view to see the Earth, since it blocks the light of the Sun. And as the stars move in our dynamic cosmos, this point of view is won and lost, “explains Lisa Kaltenegger, director of the Carl Sagan Institute at Cornell University and leader of the work that publishes the journal Nature.
Using data from the Gaia space observatory, an ongoing project to map the Milky Way in three dimensions, the experts sought to determine whether any alien civilization could find humanity with the tools we use to find exoplanets.
Earth Transit Zone
That’s how it went. Astronomers have identified 1,715 star systems up to 326 light-years distant from Earth (or 100 parsecs), whose hypothetical inhabitants could have seen Earth cross in front of the Sun sometime in the last 5,000 years. To this must be added another 319 stars that will reach that same position in the next 5,000 years. Those 2,034 stars had or will have “the front row seat to finding Earth as a planet in transit,” says Jackie Faherty of the American Museum of Natural History in New York City and a co-author of the study.
What’s more, 75 of the stars are close enough that man-made radio waves have already reached them , and seven of those stars have potentially habitable planets. Of the systems that have been or will be in the Earth’s Transit Zone, seven are known to host exoplanets, some may even be habitable, such as Ross-128, TRAPPIST-1, and Teegarden’s star.
The Ross 128 system , with a red dwarf host star located in the constellation Virgo, is about 11 light years distant and is the second closest system with an Earth-size exoplanet – its world is about 1.8 times the size of our planet.
The Trappist-1 system, located 45 light-years from Earth, is home to seven transiting Earth-size planets, four of them in the temperate and habitable zone of that star.
Teegarden’s star is about 12 light years distant and has at least two potentially habitable planets.
“Our analysis shows that even the closest stars generally spend more than 1,000 years at a vantage point where they can see the Earth’s transit,” Kaltenegger clarifies. “If we assume the opposite is true, that provides a healthy timeline for nominal civilizations to identify Earth as an interesting planet.”
Referencia: L. Kaltenegger and J.K. Faherty. Past, present and future stars that can see Earth as a transiting exoplanet. Nature. Published June 23, 2021. doi:10.1038/s41586-021-03596-y.
