Our solar system no longer has the most number of planets of any known star systems. The discovery of a new exoplanet has lead to the discovery of a star system with a total of eight planets, like our own planetary neighborhood.
The Kepler-90 system [Image by NASA/Wendy Stenzel]
Scientists working on the Kepler mission, which seeks out distant planets, found an exoplanet orbiting a star called Kepler-90. Kepler-90 lies 2,545 light years away from Earth in the constellation Draco, and has been found to be bigger and hotter than our sun. The newly discovered planet, known as Kepler-90i, turned out to be the smallest of eight planets orbiting Kepler-90.
NASA’s Kepler space telescope detected the existence of Kepler-90i when it recorded a momentary blip in Kepler-90’s brightness. These small changes in brightness usually indicate that a planet has crossed the face of a star. So far, Kepler has detected over 4,000 blips that may be planets, and around 2,525 of these have already been confirmed. However, astronomers were initially unable to manually detect the existence of Kepler-90i.
Artist's impression of the Kepler space telescope [Photo by NASA/Wendy Stenzel, Ames Research Center]
While Kepler has certainly been a prolific discoverer of planets, astronomers at NASA were convinced that there were more planets to be found in the telescope’s data. Who better to ask for help in making sense of piles upon piles of data than Google?
Christopher Shallue, a machine learning researcher at Google, and NASA astronomer Andrew Vanderburg teamed up to train a neural network on how to sniff out planets that humans may have missed among Kepler’s light readings. Kepler-90i as well as another planet, Kepler-80g, had weak transit signals that previous manual searches missed, but the neural network was able to detect them. Shallue and Vanderburg published a study describing the neural network, as well as the process of detecting the weaker signals.
Size comparison between the Kepler-90 planets and the planets in our solar system [Photo by NASA/Wendy Stenzel, Ames Research Center]
Kepler-80g is about the size of Earth and is the sixth known planet in its system. It takes 14.6 days to orbit its star, Kepler-80, which is smaller and redder than the sun. Kepler-90i, meanwhile, is slightly bigger than Earth and takes 14.4 days to orbit its star. Coincidentally, like Earth, Kepler-90i is also the third rock from the star it orbits.
The Kepler-90 system has been known to astronomers since 2013, but only seven planets were known to scientists. Kepler-90i, the eight planet to be discovered, has brought the Kepler-90 system to a tie with our solar system.
All the Kepler-90 planets are quite close together. [Photo by NASA/Wendy Stenzel, Ames Research Center]
The two planets that orbit Kepler-90 closer than Kepler-90i are also quite small, and the planets after Kepler-90i get progressively bigger. Interestingly, however, all eight of Kepler-90’s planets are stuffed together within the same distance as Earth’s distance from the sun. "The Kepler-90 star system is like a mini version of our solar system,” Vanderburg says. “You have small planets inside and big planets outside, but everything is scrunched in much closer.”
"For the first time since our solar system planets were discovered thousands of years ago, we know for sure that our solar system is not the sole record holder for the most planets," Vanderburg adds. So if Kepler-90’s system is similar to ours, is Kepler-90i habitable? Unfortunately, no. Vanderburg says that it’s not a planet he’d ever like to visit. “The surface is likely scorching hot, we calculated that it probably has an average temperature of about 800 degrees Fahrenheit.”
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