Discovery of new planet reveals distant solar system to rival our own

December 14, 2017 by Rebecca Johnson, University of Texas McDonald Observatory
The Kepler-90 planets have a similar configuration to our solar system with small planets found orbiting close to their star, and the larger planets found farther away. In our solar system, this pattern is often seen as evidence that the outer planets formed in a cooler part of the solar system, where water ice can stay solid and clump together to make bigger and bigger planets. The pattern we see around Kepler-90 could be evidence of that same process happening in this system. Credit: NASA/Ames Research Center/Wendy Stenzel

The discovery of an eighth planet circling the distant star Kepler-90 by University of Texas at Austin astronomer Andrew Vanderburg and Google's Christopher Shallue overturns our solar system's status as having the highest number of known planets. We're now in a tie.

The newly discovered Kepler-90i—a sizzling hot, rocky planet orbiting its star once every 14.4 days—was found using computers that "learned" to find in data from NASA's Kepler space telescope. Kepler finds distant planets beyond the solar system, or exoplanets, by detecting the minuscule change in brightness when a planet transits (crosses in front of) a star.

Vanderburg, a NASA Sagan fellow at UT Austin, and Shallue, a Google machine learning researcher, teamed up to train a computer to learn how to identify signs of an exoplanet in the light readings from distant recorded by Kepler. Similar to the way neurons connect in the human brain, this "neural network" sifted through the Kepler data to identify the weak transit signals from a previously missed eighth planet orbiting Kepler-90, a sun-like star 2,545 light-years from Earth in the constellation Draco.

"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 said.

Other planetary systems, though, would probably hold more promise for life than Kepler-90's system, which packs all eight planets closer to the host star than Earth is to the sun. In our solar system, only Mercury and Venus orbit between our planet and our sun. About 30 percent larger than Earth, Kepler-90i is so close to its star that its average surface temperature is thought to exceed 800 degrees Fahrenheit, on a par with Mercury. The outermost planet, Kepler-90h, is a gas giant that is about the size of Jupiter, circling with a "year" of 331.6 days.

"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," Vanderburg said.

The research paper reporting this finding has been accepted for publication in The Astronomical Journal.

The idea to apply a neural network to Kepler data came from Shallue, a senior software engineer at Google AI, a research team at the search-engine giant in Mountain View, California. Shallue became interested in exoplanet discovery after learning that astronomy, like other branches of science, is rapidly becoming inundated with data as the technology for collecting data from space advances.

"Machine learning really shines in situations where there is so much data that humans can't search it for themselves," Shallue said.

Kepler's four-year data set, for example, consists of about 2 quadrillion possible orbits of planets. To verify the most promising signals of planets, automated tests, or sometimes human eyes, are typically used, but often the weakest signals are missed during this process. So, Shallue and Vanderburg thought there could be some more interesting exoplanet discoveries lurking in the data.

The two developed a neural network to search Kepler data for . First, they trained the neural network to identify transiting exoplanets in a set of 15,000 previously vetted signals from the Kepler exoplanet catalog. Then, with the neural network having "learned" to detect the pattern of a transiting , the researchers pointed their model at 670 star systems that already had multiple known planets and searched for weaker signals. Their assumption was that multiple-planet systems would be the best places to look for more exoplanets.

Kepler-90 had already made its mark in 2013 as the first seven-planet system identified with Kepler, but the signal from the eighth planet was so weak it was missed by previous methods.

"We got 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."

Kepler-90i wasn't the only jewel this sifted out. In the Kepler-80 system, they found a sixth planet. This one, the Earth-size Kepler-80g, and four of its neighboring planets form what is called a "resonant chain," where the planets are locked by their mutual gravity in a rhythmic orbital dance. The result is an extremely stable system, similar to the seven planets in the TRAPPIST-1 system, so precisely balanced that the length of Kepler-80g's year could be predicted with mathematics.

Explore further: Finding a 'lost' planet, about the size of Neptune

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14 comments

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Paul0001
1 / 5 (5) Dec 14, 2017
This was "the big" discovery?
maholmes1
1.7 / 5 (6) Dec 14, 2017
No. Using the widely accepted but non-IAU geophysical definition of planet, Sol has either 10 or 13 known planets, not 8. If a celestial object is in hydrostatic equilibrium (is spherical or oblate in shape); orbits its parent star independently rather than orbiting a planet, or has no parent star; and is not self-luminous, geophysically, it is a planet. Known objects meeting this definition that orbit our Sun include: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Makemake, Haumea, and Eris. Some would add a 2000-kilometer minimum diameter to that, which would disqualify Ceres, Makemake and Haumea. Either way, this star still has more than 8 planets.
maholmes1
3.3 / 5 (3) Dec 14, 2017
This was "the big" discovery?


(nods) A star other than our own with 8 planets. Somewhat interesting, from my perspective, but hardly the astronomical discovery of the century.
setnom
4.2 / 5 (5) Dec 14, 2017
Manage your expectations, people.
laurele
1.8 / 5 (5) Dec 14, 2017
Our solar system does not have only eight planets, and it is disappointing to hear the presenters of this data pass off one view in an ongoing debate as fact. According to the geophysical planet definition, which does not require an object to "clear its orbit" to be a planet, and puts priority on objects' intrinsic properties rather than their locations, dwarf planets are planets too; they are simply a subclass of planets, as intended by Alan Stern, who first coined the term in 1991. With this definition, our solar system has a minimum of 13 planets and counting. Current technology is not yet able to detect dwarf exoplanets, but that does not mean we should not count them toward the total in our own solar system. At some point, we will likely find many of them in other star systems too.
AdamCC
4.8 / 5 (5) Dec 14, 2017
This was "the big" discovery?


I think the bigger deal was using a neural net to be able to find more planets in the data. A nice step forward. Bonus that it found one that's part of a high-number-of-planets system.

Not earth-shattering, but Nasa's big announcement event things never are.
Parsec
4.6 / 5 (9) Dec 14, 2017
Please people, the definition of a planet is well established. We all know the old definition. Trying to relitigate this old controversy every time a planet is discovered is ludicrous.
maholmes1
1.5 / 5 (2) Dec 15, 2017
I hate to tell you this, but the issue is not settled. Planetary scientists continue to use the geophysical definition of planet, which makes a lot more sense, so get used to this.
petersonwalter
5 / 5 (3) Dec 15, 2017
"This was "the big" discovery? "

See how blase we have become about this? 30 years ago such a discovery would have been earth shaking.
torbjorn_b_g_larsson
1 / 5 (1) Dec 16, 2017
Cool! And Trappist-1 has 7 planets, so the tail of planet observations may go further.

@maholms, laurele: Re "the widely accepted but non-IAU geophysical definition": so not accepted then as the IAU set a democratic standard. Also, you may want to check up on the definition and its universal application when establishing old enough (stably orbiting enough) planets.

And also goalpost moving away from astronomy of tallying planet observations and how huge the discovery is. Please acknowledge that few if any here share your sentimental sentiment, but are generally interested in the science and its results. Sure, we use the geophysical definition - when it is useful. Here it was not, it was confusing, inapplicable and contrafactual (as we need the astronomical definition to go with both the observation and its implications).
maholmes1
not rated yet Dec 16, 2017
@maholms, laurele: Re "the widely accepted but non-IAU geophysical definition": so not accepted then as the IAU set a democratic standard.
Please acknowledge that few if any here share your sentimental sentiment, but are generally interested in the science and its results. Sure, we use the geophysical definition - when it is useful. Here it was not, it was confusing, inapplicable and contrafactual (as we need the astronomical definition to go with both the observation and its implications).


Funny that you and other adherents of the IAU definition think you know our motivations better than we ourselves do.Not.It's always been about the science to us.The geophysical definition is straightforward, applicable and factual as could be. It is simple and easy to use.And, the 2006 IAU vote was about as undemocratic (if that matters) as it gets.
maholmes1
not rated yet Dec 16, 2017

@maholm[e]s, laurele: Re "the widely accepted but non-IAU geophysical definition": so not accepted then as the IAU set a democratic standard. Also, you may want to check up on the definition and its universal application when establishing old enough (stably orbiting enough) planets.


Not accepted because not considered valid, not just by laypeople but within the astronomical community. Also: An object that geophysically is a planet that has an unstable orbit, is a planet with an unstable orbit.

maholmes1
not rated yet Dec 16, 2017
@maholm[e]s, laurele:

And also goalpost moving away from astronomy of tallying planet observations and how huge the discovery is.


Remarkable, definitely. Not to take away from these people's hard work and ingenuity, but this star system still has from 10 to 13 known planets. When I see a star system discovered to have 13 exoplanets, then Sol and the other star system will be tied for number of planets. Not before.

Please acknowledge that few if any here share your sentimental sentiment, but are generally interested in the science and its results. .


Nope. Neither you nor anyone else who adheres to the IAU definition of planet (which is so screwed up that even laypeople with minimal scientific knowledge can see it's screwed up) speaks for everyone working in the field of astronomy. Not by a long shot. This is a scientific debate and it continues whether you like it or not.
maholmes1
not rated yet Dec 16, 2017
Not accepted because not considered valid, not just by laypeople but within the astronomical community.


Sorry. By some within the astronomical community, mainly by people whose work involves the study of planets. Science works by consensus, not by fiat like at the 2006 IAU conference.

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