Our solar system may not be that unique after all. Researchers have discovered a star that lies 2,500 light years away with at least eight planets orbiting it, just like our sun.
The Kepler-90 system was discovered back in 2013, and was initially thought to have just seven planets.
But earlier this year, a pair of researchers decided to take a closer look at the massive store of data collected by the Kepler space telescope.
Christopher Shallue and Andrew Vanderburg used artificial intelligence technology to train a computer to recognize signatures of a planet crossing in front of a star, which is known as a transit.
The computer scanned the Kepler data and recognized — with more than 90 per cent certainty — an eighth planet hiding in the Kepler-90 system.
"Machine learning really shines in situations where there is so much data that humans can't search it for themselves," said Shallue, a senior software engineer at Google AI and lead author of the paper accepted for publication in The Astronomical Journal.
Strange new worlds
Shallue and Vanderburg's exoplanet — a planet orbiting a star other than our own — is called Kepler-90i.
It's roughly 30 per cent larger than Earth and likely rocky with no gas atmosphere.
It's not exactly hospitable.
"It's not a place I'd like to go visit," said Vanderburg, an astronomer and NASA Sagan postdoctoral fellow at the University of Texas, Austin. "The surface is likely scorching hot at 800 F [427 C]."
All the planets in Kepler-90 have tighter orbits compared to the Earth's track around the sun. A year on Kepler-90i lasts 14.4 days.
Shallue and Vanderburg's neural network — which is a computer modelled on the human brain and capable of learning — also found another exoplanet in a different star system.
This new planet, called Kepler-80g, is roughly the size of Earth and part of a six-planet system around a sun that's cooler than our own. The planets are tightly packed around the star, with orbits that take less than 14 days.
The researchers say they plan to use the same method to search the remaining 150,000 stars the Kepler space telescope has studied so far.
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As for Kepler-90, there's the chance more worlds orbit its star.
"There's lots of unexplored real estate in Kepler system and it would almost surprise me if there weren't more planets in this system," Vanderburg said.
In fact, as discoveries continue, he said there may come a day when our eight-planet system will seem small.
Jessie Dotson, Kepler project scientist at NASA's Ames Research Center in California's Silicon Valley, said the understanding of planetary systems has come a long way since Kepler launched eight years ago.
To date, the project has confirmed the existence of 2,525 exoplanets.
"That's a pretty good haul," he said. "I'm so excited to see where this goes next."