Scientists have identified thousands of nearby star systems where alien life as we know it may not only exist but has already detected humanity.
Researchers from Cornell University and the American Museum of Natural History have determined 2,034 star systems in proximity to Earth – within 326 light-years of our little blue planet – where alien life as we know it could have potentially discovered humanity by observing our world crossing the Sun.
Since the dawn of human civilisation around 5,000 years ago, there have been 1,715 star systems that are perfectly situated in the cosmos to observe Earth, with a further 319 in line for their front-row seat over the next 5,000 years, meaning alien life as we know it – or do not know it – , may know more about our existence than we do.
Their research is published in Nature.
Lisa Kaltenegger, professor of astronomy and director of Cornell’s Carl Sagan Institute, said: “From the exoplanets’ point-of-view, we are the aliens. We wanted to know which stars have the right vantage point to see Earth, as it blocks the Sun’s light, and because stars move in our dynamic cosmos, this vantage point is gained and lost.”
The quest for alien life as we know it
To conduct their investigation, Katenegger and Jackie Faherty, the co-author of the study and senior scientist at the American Museum of Natural History, utilised the European Space Agency’s Gaia eDR3 catalogue to analyse which stars enter and exit the Earth’s transit zone and the duration of their stay.
“Gaia has provided us with a precise map of the Milky Way galaxy, allowing us to look backwards and forward in time and to see where stars had been located and where they are going,” Faherty said.
The scientists distinguished that of the 2,034 star systems travelling in the Transit zone of Earth throughout the observed period of 10,000 years, there are 117 objects within the vicinity of 100 light-years of our Sun, with 75 of these positioned in the transit zone since radio stations started broadcasting into space over 100 years ago.
“Our solar neighbourhood is a dynamic place where stars enter and exit that perfect vantage point to see Earth transit the Sun at a rapid pace,” Faherty commented.
Seven of these star systems have been identified to host exoplanets – all with the potential to use similar transit techniques to have discovered Earth. By observing how an exoplanet transits its Sun, the atmosphere can be analysed as it is backlit by the star, meaning alien life as we know it could detect our atmosphere’s chemical signatures of life.
The most promising contenders
For example, the Ross 128 system, which is hosted by a red dwarf star situated in the Virgo constellation, is the second-closest system with an Earth-sized exoplanet (1.8 times larger) and round 11 light-years away. Here, any alien occupants would have had a 2,158-year window to observe the Earth’s transit, starting around 3,057 years ago, losing their view around 900 years ago.
The Trappist-1 system, positioned 11 light-years away, will not be able to enter our transit zone for another 1,642 years; however, they may provide our best opportunity to find alien life when they do. This is because the system hosts seven Earth-sized planets, four of which are within the habitable zone of their host star and will remain in the transit zone for 2,371 years.
Kaltenegger said: “Our analysis shows that even the closest stars generally spend more than 1,000 years at a vantage point where they can see Earth transit. If we assume the reverse to be true, that provides a healthy timeline for nominal civilisations to identify Earth as an interesting planet.”
Moving forward, there are numerous space projects aiming to build upon this novel research; the soon to be launched James Webb Space telescope will examine multiple transiting worlds to search for signs of life and to characterise their atmosphere’s and composition. The Breakthrough Starshot initiative will launch nano-sized spacecraft to an exoplanet located 4.2 light-years away located around Proxima Centauri, which will comprehensively analyse the world.
“One might imagine that worlds beyond Earth that have already detected us are making the same plans for our planet and solar system,” said Faherty. “This catalogue is an intriguing thought experiment for which one of our neighbours might be able to find us.”