"Since Kepler looks for the shadow of the planet as it passes in front of the star, it's good at identifying planets really close to their stars," study author Rahul I. Patel, a PhD student at Stony Brook University, told The Post. "To get a good look at a planet that's the same distance from its star as Earth is from the sun, you'd have to wait, say, three years to see three passes."
But if a planet has an orbit that takes more than a couple of years, the waiting game to confirm its existence can stretch on for a lifetime.
That's where GPI comes in: It's suited for small, distant planets.
"This looks at really far out planets — no pun intended," Patel said.
And the younger, the better — since they're still hot from their creation, young planets will glow more brightly in infrared.
"Finding these exoplanets is difficult," Patel explained. "You're basically looking for a firefly that's really close to a flood lamp, standing about a mile away and looking through a glass of water."
The water, he said, is the atmosphere, which blurs the light of the host star. GPI has to cancel out the star's light (turning off the flood lamp) and then correct for the distortion caused by the atmosphere, which blurs the glow of the planet as well.
To confirm the planet, the GPI can then analyze its chemical fingerprint.
In this case, that analysis produced a planet about twice the mass of Jupiter — the smallest exoplanet ever imaged — that orbits at about the same distance as Saturn. It's also much colder, at 800 degrees Fahrenheit, and has unusually strong signs of methane.
All of that points to a sort of baby Jupiter — a planet much like we believe Jupiter was in its infancy, albeit hotter.
"51 Eri b is the first one that's cold enough and close enough to the star that it could have indeed formed right where it is the 'old-fashioned way," lead study author Bruce Macintosh, a professor of physics at Stanford University who heads the GPI project, said in a statement. "This planet really could have formed the same way Jupiter did — the whole solar system could be a lot like ours."
And there's more: This solar system, home to a sun just 20 million years old, features a pair of dust belts that could be just like the ones in our solar system.
Our neighborhood is sandwiched by two dust belts, which contain the remnants of planet formation. There's a warm dust belt — the asteroid belt between Mars and Jupiter — and the cold dust belt, the Kuiper, which borders the edge of the solar system and is home to mysterious objects such as Pluto.
According to data from the GPI and NASA's Herschel telescope, 51 Eri's solar system is sandwiched by hot and cold dust belts as well.
"This architectural similarity to our own system sort of hints at something that might look like what our solar system did early on," Patel said. It's not guaranteed that this younger system will evolve the same way ours did, but it certainly could.
For now, the researchers will work on studying the new planet's orbit and better pinning down its chemical makeup, as well as keeping an eye out for more planets within the system.