We have discovered more than 4,000 planets orbiting distant stars. They are a diverse group, from hot Jupiters that orbit red dwarf stars in a few days to rocky Earth-like worlds that orbit Sun-like stars. With spacecraft such as Gaia and TESS, that number will rise quickly, perhaps someday leading to the discovery of a world where intelligent life might thrive. But if we can discover alien worlds, life on other planets could find us. Not every nearby star would have a good view of our world, but some of them would. New work in the Monthly Notices of the Royal Astronomical Society tries to determine which ones.

Most of the exoplanets we’ve discovered have been found by the transit method. This is where the planet passes between its star and our view from Earth, blocking some of the starlight. As the planet passes by, the star dims slightly. From this periodic dimming, we know the planet exists. There are other ways to find exoplanets, such as the Doppler method, but the transit method is the easiest.

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