Here's what we know about the real alien planet inspiring 'Pluribus'

In Apple TV’s Pluribus, a faint radio signal from deep space reshapes humanity, and the source, astronomers learn, is Kepler-22b, a world that exists far beyond our solar system. 

During episode 8, Carol and Zosia look for its star through a telescope. 

"I’m not sure I’m looking in the right spot," Carol says. "I mean, I see the Swan, I think."

After getting her bearings — and Zosia eliminating the light pollution by turning off all the lights — Carol announces she sees the star, Kepler-22. 

"And the planet, which you can’t see, is Kepler-22b. That’s our name for it. We have no idea what they call it," Zosia says. "Sometimes we close our eyes and try to picture it."

For fans wondering how much science sits behind the fiction, the answer is more than you might think. But what we actually know about this real exoplanet is far less than scientists would like. (We don't have a hive mind working it.)

Is Kepler-22b a real planet?

NASA discovered Kepler-22b in 2009 using data from its namesake, the Kepler Space Telescope, a mission designed to look for planets around other stars. Other observatories were used to confirm the findings in 2011. 

But Kepler did not grab a photo of the planet. Instead, it watched for tiny dips in a star’s brightness. When a planet crosses in front of its star, it blocks a small amount of light. Catch that dimming a few times at regular intervals, and astronomers can validate the existence of a planet. This is called the "transit method" of planet detection, but you can think of it as watching for cosmic blinks.

"Fortune smiled upon us with the detection of this planet," said William Borucki, who led the team that discovered Kepler-22b, in a statement back then. "The first transit was captured just three days after we declared the spacecraft operationally ready. We witnessed the defining third transit over the 2010 holiday season."

Kepler-22b sits within its star's habitable zone, where temperatures could allow liquid water to exist on a planet's surface. Credit: NASA / Ames / JPL-Caltech infographic

Does Kepler-22b have air and water?

Kepler-22b orbits a star similar to the sun, though it's slightly smaller and cooler. One full trip around that G-type star takes about 290 days — close to Earth’s year. That timing matters, because it places Kepler-22b in what many scientists call the "habitable zone." This is the region around a star where temperatures could allow water to exist on a planet's surface in liquid form, assuming the world has the right kind of atmosphere. Liquid water matters because every form of life people know about depends on it.

That detail helped fuel news headlines calling Kepler-22b a "new Earth" or "Earth's twin" more than a decade ago. But the reality is more complicated.

Kepler-22b is bigger than Earth. Its radius is roughly two times larger. For now, that puts it in a category scientists call a "super-Earth." The name sounds dramatic, but it only means "bigger than Earth, smaller than Neptune." And, no, it's not necessarily a souped-up version of home.

This Tweet is currently unavailable. It might be loading or has been removed.

Is Kepler-22b a rocky world like Earth?

In fact, scientists don't know what Kepler-22b is made of. It could be rocky, like Earth. It could be covered by an ocean. Or it could resemble a mini-version of Neptune, wrapped in thick gas with no solid surface at all (although, truth be told, we might not even know Neptune's makeup, as Mashable recently reported). All of those possibilities fit the measurements astronomers can make so far.

Its temperature is also uncertain. Models suggest that if Kepler-22b had an atmosphere similar to Earth’s, its surface could be around 72 degrees Fahrenheit. But atmospheres trap heat differently. A thicker atmosphere like Venus' could make the planet much hotter, causing liquid to evaporate, while a thinner one like Mars' could leave it frigid. 

What makes Kepler-22b special?

What Kepler-22b does represent is a milestone. It was the first confirmed planet squarely inside the habitable zone of a sun-like star. Its discovery showed that planets close to Earth’s size, on Earth-like orbits, are not impossible to find. Kepler went on to identify thousands more candidates, many smaller and cooler than the early finds.

Apple TV's "Pluribus" spotlights Kepler-22b, a real habitable-zone exoplanet discovered by NASA that remains a scientific mystery. Credit: Apple TV

Can a spacecraft visit Kepler-22b?

Pluribus imagines Kepler-22b as an ocean world that sends a gift to humanity through radio waves. In real life, no such signals have arrived, no RNA instructions lurk in the static, and no shared consciousness has helped engineers build a faster-than-light-speed spacecraft. 

The planet's extreme distance from Earth adds a hard limit. Kepler-22b sits about 640 light-years away. At highway speeds of 60 mph, a road trip there would take about 7 billion years. Even the Voyager 1 spacecraft, zooming through interstellar space at 38,000 mph right now, would take 11 million years to get there. 

That's at least one way the show remains loyal to the astronomical facts. Carol asks what the "people" there are like. 

"We’ll probably never learn the first thing about them," Zosia says. "They’re too far away."