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Four mini-Neptunes orbiting in lock step

For every three orbits of the outermost planet orbiting the star Kepler-223, the second planet orbits four times, the third six and the innermost eight.

Astronomers from the University of Chicago and University of California, Berkeley, announced on May 11, 2016 that their analysis of a four-planet system – discovered several years ago by the Kepler spacecraft – reveals something interesting and rare. The four Neptune-size planets around the star Kepler-223 – all nestled close to the star – are orbiting in a unique resonance that has been locked in for billions of years. For every three orbits of the outermost planet, the second orbits four times, the third six times and the innermost eight times.

These scientists reported their discovery online May 11 in the journal Nature. Their statement said:

Such orbital resonances are not uncommon – our own dwarf planet Pluto orbits the sun twice during the same period that Neptune completes three orbits – but a four-planet resonance is.

[We] are particularly interested in this stellar system because our system’s four giant planets – Jupiter, Saturn, Neptune and Uranus – are thought to have once been in resonant orbits that were disrupted sometime during their 4.5-billion-year history.

The Kepler-223 star system can help us understand how our solar system and other stellar systems discovered in the past few decades formed.

In particular, it could help resolve the question of whether planets stay in the same place they formed, or whether they move closer to or farther from their star over the eons.

Read more about the four planets in lock step around their star, from BerkeleyNews

The arrangement and relative sizes of the four planets around Kepler-223, though not to scale. One AU (astronomical unit) is 93 million miles, the distance between Earth and sun in our solar system. Image via BerkeleyNews

Arrangement and relative sizes of the four planets around Kepler-223 (not to scale). One AU (Astronomical Unit) is 93 million miles, the distance between our Earth and sun. Image via BerkeleyNews

Bottom line: The star Kepler-223 has four Neptune-sized planets – close to their star – orbiting in a unique resonance.

Deborah Byrd

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