With eight planets whirling around its sun, our solar system has held the galactic title for having the most known planets of any star system in the Milky Way.
But on Thursday NASA announced the discovery of a new exoplanet orbiting a distant star some 2,500 light years away from here called Kepler 90, bringing that system’s total to eight planets as well. The new planet, known as Kepler-90i, is rocky and hot. It orbits its star about once every 14 days.
The finding was made using data collected by NASA’s Kepler Space Telescope, a planet hunter that has spotted more than 2,500 confirmed exoplanets since its launch in 2009. Unlike those previousdiscoveries, the new exoplanet was detected with the help of artificial intelligence researchers at Google using a machine learning technique called neural networking.
“This is the first time a neural network specifically has been used to identify a new exoplanet,” said Christopher Shallue, a software engineer at Google who helped make the finding.
The technology, which is loosely inspired by the human brain, is designed to recognize patterns and classify images. It can learn to tell the difference between something simple like a cat and a dog, and also to distinguish exoplanets from cosmic noise.
For the project, the computer looked at a small chunk of data gathered by Kepler from 2009 to 2013. Of the 150,000 stars represented in Kepler’s collection, the computer combed through 670 star systems for signs of exoplanets.
Astronomers spot exoplanets when the celestial bodies move, or transit, in front of their stars. The interaction causes a dip in brightness that creates a detectable signal. So far, the data set has about 35,000 such signals. The astronomers trained the program on a set of about 15,000 signals, and it identified planets correctly 96 percent of the time.
The neural network learned what was a planet and what was not a planet and was able to find the exoplanet Kepler-90i, as well as a second exoplanet named Kepler-80g around a different star system. Next, the researchers plan to explore more star systems studied by Kepler.
“We plan to search all 150,000 stars in the Kepler data system,” said Mr. Shallue.
Andrew Vanderburg, an astronomer at the University of Texas, Austin, said that Kepler-90i is about 30 percent larger than Earth and about as hot as the planet Mercury, reaching about 800 degrees Fahrenheit.
Like the other seven planets in its system, it is packed close to its star. It resembles a miniature version of our solar system, he said, where the most distant known planet is about as far away from its star as the Earth is from our sun. But there could be additional, more distant planets not yet detected because planets close to their stars may be easier for astronomers to find.
Seth Shostak an astronomer with the SETI Institute in Mountain View, Calif., who was not involved in the project said the finding that Kepler 90 has eight planets shows that our solar system is “just another duck in a row.”
“The bad news is we’re not quite as special as we thought we were,” he said. “But the good news is we may have a lot of cosmic company.”
It’s possible that the two systems may not be tied for long as astronomers search the outer reaches of our solar system for the elusive Planet Nine. It sets the stage for a new space race: Which team will break the intragalactic deadlock? Will artificial intelligence first detect another planet in the Kepler-90 system, or will astronomers find a distant ninth planet orbiting our sun?
“It’s kind of cool to see which one will be proven next,” said Jessie Dotson, Kepler’s project scientist at NASA.
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