Nasa's Kepler space telescope has discovered an eighth planet in a distant star system called Kepler 90 - the first time a faraway star has been found to have the same number of planets orbiting it as our own sun.
Although the solar system, Kepler 90, is not new, the eighth planet, Kepler 90i, was found using AI software in a groundbreaking project between Google and NASA.
Our @NASAKepler mission's search for new planets teamed with machine learning to discover another solar system with an 8th planet that is 2,500 light-years away. Here’s what you need to know about the #Kepler90 discovery: https://t.co/2JpIr7p4pE pic.twitter.com/nqvLw5mlSv
— NASA (@NASA) December 14, 2017
The discovery of a system identical to our own raises hopes of finding alien life.
The Kepler-90 planets have a similar configuration to our solar system, with small planets orbiting close to their star and the larger planets found farther away.
The new planet, estimated to be about 30 percent larger than Earth, is 'not a place you'd like to visit,' said Andrew Vanderburg, astronomer and Nasa Sagan Postdoctoral Fellow at The University of Texas, Austin.
"It is probably rocky, and doesn't have a thick atmosphere". And, temperatures at the surface are "scorching".
According to Vanderburg, the average surface temperature is likely around 427 degrees Celsius.
The Kepler planet hunting satellite has been searching the stars for distant worlds using Google's AI system, which used machine learning to "find" planets in the Kepler data with up to 96 per cent accuracy.
Neural networks can be trained on huge amounts of data to determine the difference between different objects with great accuracy, the team explained in the teleconference.
Much like an AI can learn to spot the difference between cats and dogs, it can spot the difference between patterns associated with planets, and other types of patterns in the cosmos that could be false positives.
"After showing our model 15,000 signals, the neural network learned how to distinguish patterns from actual planets from patterns that are caused by other objects," said Christopher Shallue, senior software engineer at Google AI in Mountain View, California.
AI takes on a new mission: planet hunting. See how we used machine learning to hunt for new planets in @NASAKepler data–and actually found one → https://t.co/ycI0xXetdi pic.twitter.com/zsjQZQdyYy
— Google (@Google) December 14, 2017
He worked on the system as part of his "20 per cent time" at the company, where employees are allowed to work on anything they want.
"We used our model to identify two new planets from a set of 670 stars," Shallue explained.
"One of these two planets is called Kepler 80g.
"The planet we are focusing on today is called Kepler 90i, which is the eighth planet in its star system."
"This is a really exciting discovery, and we consider it to be a success," in the use of neural networks in the search for distant worlds, the expert explained.
The star system sits roughly 2545 light-years from Earth in the constellation Draco, and of the new planets found, Kepler 90i is the "smallest of the bunch".
The new planet orbits its star once every 14.4 days.
But, all of the planets in this system 'tightly' orbit their star, which is thought to be cooler than our own sun, meaning their orbital periods are relatively short.
Before the latest AI-guided results, "Kepler 90 was tied with Trappist-1, with 7 planets each," says Jessie Dotson, Kepler project scientist at NASA's Ames Research Center in California's Silicon Valley.
"But now, it ties with our own system with the most known number of planets" around a star.
The Kepler 90 system was first discovered back in 2013. It was the first seven-planet system identified with the telescope.
But, the eighth planet remained undetected for years – until Google's AI picked up on its "weak" signal.
The AI uses light readings from distant stars to identify potential signs of a planet – and, after training on thousands of previously vetted signals, it was able to spot the previously missed patterns of the elusive eight planet.
"We get lots of false positives of planets, but also potentially more real planets," Vanderburg said.
"It's like sifting through rocks to find jewels. If you have a finer sieve, then you will catch more rocks, but you might catch more jewels as well."
The latest discovery is not just a planet candidate; according to Nasa, tit has been confirmed to be "almost certainly" an exoplanet, with 1 in 10,000 false positive probability.
While the discovery is exciting, this particular system isn't the most promising for the possibility of hosting life.
All of its planets are packed close to the star.
All eight planets of Kepler 90 sit closer to their host star than Earth is to the sun; in our own solar system, on the other hand, only Mercury and Venus have such tight orbits.
Kepler 90i is about as hot as Mercury, while the outermost planet in the system, Kepler 90h, is a gas giant roughly the size of Jupiter.
The other newly discovered planet, Kepler-80g, is now known to be the sixth in the system.
It's roughly the size of Earth - and, it's four neighbouring plantes form a "resonant chain", which locks the planets into a rhythmic 'orbital dance,' that likely stabilizes the system.
The Kepler mission has spotted thousands of exoplanets since 2014, with 30 planets lessthan twice the size of Earth now known to orbit within the habitable zones of their stars.
Further studies have been able to detect some of these planet's atmospheres, and the Google AI have been used to look through this data to find potentially habitable worlds.
Launched in 2009, the satellite has helped in the search for planets outside of the solar system that orbit within the habitable zone of their stars.
Last summer, astronomers revealed they'd discovered 197 new planet candidates, and confirmed 104 planets through the Kepler mission.
The planets, which are all between 20 and 50 per cent larger than Earth by diameter, orbit the M dwarf star K2-72, found 181 light years away.
At the time, the researchers, led by the University of Arizona, said the possibility of life on planets around a star of this kind cannot be ruled out.
Since its launch, the Kepler mission has been plagued by several setbacks, but has continued to spot new objects outside of the solar system.
In its initial mission, Kepler surveyed just one patch of sky in the northern hemisphere, measuring the frequency of planets whose size and temperature might be similar to Earth orbiting stars similar to our sun.
In the spacecraft's extended mission in 2013, it lost its ability to precisely stare at its original target area, but a fix created a second life for the telescope.
After the fix, Kepler started its K2 mission in 2014, which has provided an ecliptic field of view with greater opportunities for Earth-based observatories in both the northern and southern hemispheres.
Because it covers more of the sky, the K2 mission is capable of observing a larger fraction of cooler, smaller, red-dwarf type stars.
The newly-discovered Kepler-90i is a sizzling hot, rocky planet that orbits its star once every 14.4 days.
It is 30 per cent larger than Earth, and with a surface temperature of approximately 800°F - not ideal for your next vacation.
It also orbits its star every 14 days, meaning you'd have a birthday there just about every two weeks.
The Kepler 90 star system sits roughly 2,545 light-years from Earth, in the constellation Draco.
Kepler searches stars within our region of the Milky Way galaxy for signs of rocky planets where liquid water might exist on the surface.
The telescope has an incredibly sensitive instrument known as a photometer that detects the slightest changes in light emitted from stars.
It tracks 100,000 stars simultaneously, looking for telltale drops in light intensity that indicate an orbiting planet passing between the satellite and its distant target.
When a planet passes in front of a star as viewed from Earth, the event is called a 'transit'.
Tiny dips in the brightness of a star during a transit can help scientists determine the orbit and size of the planet, as well as the size of the star.
Based on these calculations, scientists can determine whether the planet sits in the star's 'habitable zone', and therefore whether it might host the conditions for alien life to grow.
Kepler mission
Candidate exoplanets: 4496
Confirmed exoplanets: 2341
Confirmed exoplanets less than twice Earth-size in the habitable zone: 30
K2 mission (2014-present)
Candidate exoplanets: 515
Confirmed exoplanets: 184
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