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Kepler-223 system provides clues about planetary migration


An artist’s concept of NASA’s Kepler space telescope. Image Credit: NASA

At first, the four exoplanets that make up the planetary system Kepler-223 seemed to have little in common with the planets of our own solar system. In a recent study, scientists using data from NASA’s Kepler space telescope found that the two systems may have had more in common in the distant past.  

The Kepler-223 planets orbit their star in the same approximate configuration that Jupiter, Saturn, Uranus, and Neptune may have had early in the history of our solar system, before migrating to their current positions.

Sean Mills (left) and Daniel Fabrycky (right), researchers at the University of Chicago, describe the complex orbital structure of the Kepler-223 system in a new study. Photo Credit: Nancy Wong/University of Chicago

Sean Mills, left, and Daniel Fabrycky, researchers at the University of Chicago, describe the complex orbital structure of the Kepler-223 system in a new study. Photo Credit: Nancy Wong / University of Chicago

“Exactly how and where planets form is an outstanding question in planetary science,” said the study’s lead author, Sean Mills, a graduate student in astronomy and astrophysics at the University of Chicago in Illinois. “Our work essentially tests a model for planet formation for a type of planet we don’t have in our solar system.”

The four gaseous planets that orbit Kepler-223 are of a type astronomers call “sub-Neptunes” and are much more massive than Earth. They probably consist of a solid core surrounded by an envelope of gas.

Sub-Neptunes are the most common type of planets known in the galaxy, but there are no examples of them in our solar system. The planets of the Kepler-223 system orbit very close to their star and have an orbital period ranging from seven to 19 days.

“That’s why there’s a big debate about how they formed, how they got there and why don’t we have an analogous planet in our solar system,” Mills said.

Mills and his fellow researchers used data from the Kepler mission to analyze how the four planets blocked the light from their star and changed each other’s orbits. The scientists were able to calculate the planets’ masses and sizes.

The team then performed numerical simulations of planetary migration that generate this system’s current architecture, similar to the migration suspected for the gas giants of our solar system. These calculations are described in the May 11 Advance Online edition of the journal Nature.

The orbits of the four planets around Kepler-223 are in resonance. For every three orbits of the outermost planet, the second orbits four times, the third six times, and the innermost eight times. Kepler-223 is the first time that four planets in an extrasolar system have been confirmed to be in resonance.

Video courtesy of UC Berkeley


Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.

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