Smile, they could be watching us!
Such systems with stars similar to our Sun could contain planets also similar to Earth in their habitable zones and that would be able to detect the chemical traces of life on Earth.
It is a unique cosmic perspective. Are you watching us? Some exoplanets, worlds beyond our own solar system have a direct line of sight to observe the biological qualities of the Earth from very, very far away.
Specifically, experts have identified 1,004 main sequence stars that could contain Earth-like planets within what we call the habitable zone, within about 300 light years from Earth. This study could help provide targets for organizations like SETI and the Breakthrough Listen Initiative that are actively looking for signs of advanced extraterrestrial civilizations.
Earth, the target
Using the transit technique (which involves observing light from distant stars and detecting small dips in brightness that occur when an orbiting world passes between the surface of the stellar body and the eye of a telescope), scientists they can confirm the presence of exoplanets and also elucidate their atmospheres. A very useful detail in the search for extraterrestrial life, since organic life forms and industrialization leave their mark on the atmosphere of a planet.
Therefore, theoretically, our planet could also be discovered and analyzed by an alien civilization using the transit method . If they were to watch the Earth pass in front of the Sun, they would detect atmospheric chemicals that hint at our presence on this blue planet.
Scientists examined data sets from TESS and the Europa star-mapping spacecraft Gaia, looking for stars within 100 parsecs (about 326 light years) that were aligned with the ecliptic, the plane of Earth’s orbit around the Sun. Of the 1,004 stars identified, 508 “warrant a minimum 10-hour observation of the Earth’s transit” across the face of the sun, the authors wrote.
What star systems could we find?
Most of the stars, 77%, are M-type stars or red dwarfs, the smallest and coolest of the main sequence stars.
“Only a very small fraction of exoplanets will be randomly aligned with our line of sight so that we can see them transit,” explains physicist Joshua Pepper, leader of the work. “But all the stars that we identified in our article in the solar neighborhood were able to see our Earth transit the Sun, drawing their attention.”
“If we found a planet with a vibrant biosphere, we would be curious to know if someone is looking at us or not,” says Lisa Kaltenegger, co-author of the study. “If we are looking for intelligent life in the universe, with this method they could find us and they might want to make contact. We just created the star map of where we should look first.”
It stands to reason that if an alien civilization detects life biomarkers on Earth, it might try and want to communicate with us, right?
Referencia: L Kaltenegger, J Pepper. Which Stars Can See Earth as a Transiting Exoplanet? Monthly Notices of the Royal Astronomical Society: Letters, Volume 499, Issue 1, November 2020 DOI: 10.1093/mnrasl/slaa161
