NASA Finds an Eighth Planet Around a Distant Star, With Help From Google's AI

A program trained to recognize the faint dimming of a star when a planet crosses in front of it found a planet that astronomers had missed in old telescope data. The star, Kepler-90, now has as many known planets as our own sun.

NASA announced this morning that a star 2,500 light-years away called Kepler-90 has an eighth planet, tying our solar system for the most planets known around a single star. The new planet, Kepler-90i, is small and rocky and hot — about 800 degrees on its surface — and it circles its star every fourteen days. Nobody will be visiting.

The interesting part is how it was found. The Kepler space telescope, launched in 2009, watches stars for the tiny dip in brightness that happens when a planet passes in front of one. It has recorded that dip for thousands of stars, and the signals for the smallest planets are so faint that astronomers set them aside as too weak to trust. There are tens of thousands of these weak signals in the archive, far more than people can check by hand.

A Google software engineer, Christopher Shallue, working with a University of Texas astronomer, Andrew Vanderburg, trained a program to tell the difference between a real planet signal and noise, by showing it 15,000 examples that astronomers had already labeled. Then they pointed it at the leftover pile from 670 stars. It found Kepler-90i, and a second new planet around another star. Both had been sitting in the data for years.

The program is the same general kind that Google uses to recognize objects in photographs. It knows nothing about astronomy. It was shown what a planet looks like in the data and learned to spot one. The team plans to run it on the rest of the archive — 150,000 stars — to see what else was missed.