Astronomers are working hard to catalog all the exoplanets visible from Earth, but two researchers decided to figure out which exoplanets in turn have a good view of the Earth.
It turns out there are 1,004 (and growing) main sequence stars similar to the Sun, with terrestrial planets likely to detect chemical traces of life on our planet. If anyone is there, they can see us.
All of these stars are within 326 light years (100 parsecs) of Earth, and research is primarily focused on nearby exoplanets.
For the calculations, data from the NASA Transiting Exoplanet Survey Satellite (TESS) star catalog and the Gaia star map were used, and over time, the star systems that can observe the Earth will change.
“If alien observers were searching, they could see signs of the biosphere in the atmosphere of our pale blue dot,” says astronomer Lisa Kaltenegger of Cornell University. 'And we can even see some of the brightest of these stars in the night sky without binoculars or telescopes.'
To detect Earth, astronomers on these exoplanets will need to use the same methods we use to catalog distant objects: watching the Earth pass in front of the Sun to figure out the composition of our planet's atmosphere.
The Earth's ecliptic, or the plane of the Earth's orbit around the Sun, is critical to determining which exoplanets can see us from. It tells astronomers where exoplanets with a good view of the Earth will be located – in other words, from which points of deep space our Earth will seem to be a planet passing through for life.
Of the 1004 stars identified with potentially habitable zones, 508 offer their surrounding planets at least a 10-hour window of Earth observation from each orbit. Most of the stars – 77 percent – are M-type or red dwarf stars, the smallest of the main sequence stars.
“Only a very small fraction of exoplanets will accidentally align with our line of sight so we can see their passage,” says physicist Joshua Pepper of Lehigh University. “But all the thousands of stars we identified in our article can watch the Earth pass by the Sun, drawing their attention.”
The TESS space telescope has already proven phenomenal since its commissioning in 2018: it has been busy identifying our closest neighbors in space and solving mysteries at the edges of our solar system, as well as finding the most Earth-like exoplanets in space.
At the moment, the researchers think that their work could be used to narrow the search for extraterrestrial life in the future – for example, if we want to find exoplanets that could notice us, as well as us them.
“If we found a planet with a bright biosphere, we would be curious if there is someone there, if we are looking at us,” says Kaltenegger.
“If we're looking for intelligent life in the universe that could find us and might want to get in touch, we've just created a star map where we should look for it first.”
The research is published in Monthly Notices of the Royal Astronomical Society: Letters.
Sources: Photo: John Munson / Cornell University
