UCBerkeley: Star Has Four Mini-Neptunes Orbiting in Lock Step

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Star Has Four Mini-Neptunes Orbiting in Lock Step
University of California, Berkeley | 2016 May 11

[c][attachment=0]KOI_730_8-6-4-3.gif[/attachment][/c][hr][/hr]

A four-planet system observed several years ago by the Kepler spacecraft is actually a rarity: Its planets, all miniature Neptunes 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.

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.

Astronomers ... 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. ...

Four Synchronized Planets Reveal Clues to How Planets Form
Eberly College of Science | Penn State University | 2016 May 11

Quartet of Exoplanets Locked in Complex Dance
University of Chicago | 2016 May 11

A Resonant Chain of Four Transiting, Sub-Neptune Planets - Sean M. Mills et al

• Nature (online 11 May 2016) DOI: 10.1038/nature17445

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Kepler-223 System: Clues to Planetary Migration
NASA | JPL-Caltech | Ames | Kepler | 2016 May 17

[c][youtube]https://www.youtube.com/watch?v=Bi-TFHNVfwY[/youtube]Orbital evolution in Kepler-223: These animations show approximately 200,000 years of
orbital evolution in the Kepler-223 planetary system. The planets’ interactions with the
disk of gas and dust in which they formed caused their orbits to shrink toward their
star over time at differing rates. (Credit: Daniel Fabrycky and Cezary Migazewski)[/c][hr][/hr]

The four planets of the Kepler-223 star system appeared to have little in common with the planets of our own solar system today. But a new study using data from NASA's Kepler space telescope suggests a possible commonality in the distant past. The Kepler-223 planets orbit their star in the same configuration that Jupiter, Saturn, Uranus and Neptune may have had in the early history of our solar system, before migrating to their current locations.

"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 puffy, gaseous planets orbiting Kepler-223, all of which are far more massive than Earth, orbit close to their star. "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 collaborators used data from Kepler -- its mission is now known as K2 -- to analyze how the four planets block their stars' light and change each other's orbits. This information also gave researchers the planets' sizes and masses. The team performed numerical simulations of planetary migration that generate this system's current architecture, similar to the migration suspected for the solar system's gas giants. These calculations are described in the May 11 Advance Online edition of Nature.

The orbital configuration of our own solar system seems to have evolved since its birth 4.6 billion years ago. The four known planets of the much older Kepler-223 system, however, have maintained a single orbital configuration for far longer. ...