Astronomers had once calculated that billions of planets had gone rogue in the Milky Way. Now, scientists at NASA and Osaka University in Japan are upping the estimate to trillions. Detailed in two papers accepted for publication in The Astronomical Journal, the researchers have deduced that these planets are six times more abundant than worlds orbiting their own suns, and they identified the second Earth-size free floater ever detected.

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Previous findings suggested that most of these planets were about the size of Jupiter, our solar system’s most massive planet. But that conclusion garnered a lot of pushback. [...] They estimate that there are about 20 times more free-floating worlds in our Milky Way than stars, with Earth-mass planets 180 times more common than rogue Jupiters.

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Could any of these planets be habitable? Possibly, Dr. Bennett surmised, explaining that they’d be dark without a host star, but not necessarily frigid. Hydrogen in a planet’s atmosphere could act like a greenhouse and trap heat emanating from its interior — which is what sustains microbial life in deep sea vents on Earth.

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The team didn’t look beyond the bounds of the Milky Way. “But we expect that other galaxies are pretty similar,” Dr. Bennett said — meaning that these outcasts might be sprinkled across our entire universe.