At least 1,715 nearby star systems sat at a perfect angle to view Earth during the past 5,000 years, meaning aliens living in those systems, if they exist and have the right technology, could have watched our planet from afar as early human civilizations first emerged.
Of those star systems, 313 exited the special viewing zone, known as the Earth transit zone (ETZ), sometime in the past few thousand years, leaving 1,402 star systems capable of providing a glimpse of our planet today, according to a new study, published Wednesday (June 23) in the journal Nature. And over the next 5,000 years, 319 additional stars will enter the ETZ for the first time.
All of the identified stars lie within 326 light-years of the sun, and 75 of those stars are less than 100 light-years away. The team chose to search within this 326 light-year radius since that area is the focus of the European Space Agency’s Gaia mission, which aims to create a 3D map of our galaxy, and new Gaia data recently became available.
Given that humans began transmitting radio signals about 100 years ago, the 75 closest stars are near enough that “our radio waves would have washed over them already,” first author Lisa Kaltenegger, an associate professor of astronomy and director of the Carl Sagan Institute at Cornell University, told Live Science.