Many scientists had hoped that Kepler's original mission would last far longer than four years, allowing it to find a significant number of Earth-sized planets in Earth-sized orbits around sun-like stars.
A "sizzling hot, rocky planet", as described by NASA, Kepler-90i was spotted by a neural network trained to recognize exoplanets in the light readings recorded by the Kepler space observatory.
The newly discovered eighth planet, called Kepler-90i, was found using machine learning from Google. That tied the Kepler-90 system with the seven-planet Trappist-1 system for the honor of most populous known exoplanet solar system.
The data came from the Kepler telescope which NASA launched into space in 2009 as part of a planet-finding mission that is expected to end next year as the spacecraft runs out of fuel. The next three planets beyond Kepler-90i's orbit (90d, 90e and 90f) fall into a sub-Neptune size class and orbit every 60, 92 and 125 days, respectively.
NASA calculated its average temperature at about 800 degrees Fahrenheit (426 Celsius) - as hot as Mercury, the closest planet to the Sun.
"The Kepler-90 star system is like a mini version of our solar system. You have small planets inside and big planets outside, but everything is scrunched in much closer", said Vanderburg, a NASA Sagan Postdoctoral Fellow and astronomer at the University of Texas at Austin. Now, an eighth planet has been identified in this planetary system, making it tied with our own solar system in having the highest number of known planets.
Kepler 90-i lives 2,545 light-years from Earth and, like the rest of the planets in its solar system, is closer to its sun than Earth is.
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First, the researchers trained the neural network to identify transiting exoplanets using a set of 15,000 previously-vetted signals from the Kepler exoplanet catalogue.
According to AP, Shallue also said Google planned to make public the code needed to do searches for planets outside of our solar system using a home computer and the publically available Kepler data.
When the scientists finally tested their neural network on signals that it had not seen before, it correctly sorted the planets from the false positives a whopping 96% of the time, Shallue said. "It's like sifting through rocks to find jewels".
What is Kepler-90i like? In the Kepler-80 system, they found a sixth planet. Five of the six planets form a resonant chain, in which they are locked in orbit by mutual gravity.
Their findings will be published in The Astronomical Journal.
"These results demonstrate the enduring value of Kepler's mission", said Jessie Dotson, Kepler's project scientist at NASA's Ames Research Center in California.
"It would nearly be surprising to me if there weren't any more planets in around that star". After finding thousands of exoplanets in a tiny area of the night sky near the constellation of Lyra over the Milky Way, Kepler's gyroscopes were damaged in 2014.
But that isn't where its similarities to our own solar system end.