It's an unsettling thought, but aliens could easily spot Earth before humans spot them.
In a new research paper, astronomers identified 82 other stars around the sun that have a clear view of Earth. If any of those stars are host to planets with life, someone else in the universe may have already seen that humans are here.
These 82 potentially habitable stars can see Earth cross in front of the sun: http://ow.ly/JgRU300c11K #AstronomyDaypic.twitter.com/GjgTQFiBhZ
The researchers assume that alien life could theoretically figure out the same way to find exoplanets that we have.
Scientists spot exoplanets by pointing their telescopes at distant stars and waiting for a planet to pass in front of it. When that happens, they can glimpse a tiny dip in starlight:
So someone standing on a planet in another star system might be able to spot Earth the same way.
There are at least 82 other stars that sit on the same plane as the sun. That means Earth would pass directly in front of their line of sight at some point during its rotation around the sun. Additionally, these 82 stars are similar in size to the sun, and some may host Earth-like, potentially habitable planets.
But those are just the stars scientists know about. The researchers argued there could be as many as 300,000 stars with 30,000 potentially habitable planets with a clear view of Earth.
"As an ultimate consequence, even if our species chose to remain radio-quiet to eschew interstellar contact, we cannot hide from observers located in Earth's solar transit zone, if they exist," researchers wrote.
Maybe we should smile and wave?
Correction: May 16, 2016
A previous edition of this article misstated how many potentially habitable planets have a clear view of Earth. That number is 30,000.