Exoplanets’ complex orbital structure points to planetary migration in solar systems

Posted: May 13, 2016 by oldbrew in Astrophysics, Celestial Mechanics, exploration, solar system dynamics
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The Kepler-223 planetary system, which has long-term stability because its four planets interact gravitationally to keep the beat of a carefully choreographed dance as they orbit their host star. [credit: W.Rebel]

The Kepler-223 planetary system, which has long-term stability because its four planets interact gravitationally to keep the beat of a carefully choreographed dance as they orbit their host star.
[credit: W.Rebel]


As the report says: ‘Kepler-223’s two innermost planets are in a 4:3 resonance. The second and third are in a 3:2 resonance. And the third and fourth are in a 4:3 resonance.’ They are ‘far more massive than Earth’. Interesting to say the least.

The four planets of the Kepler-223 star system seem to have little in common with the planets of Earth’s own solar system. And yet a new study shows that the Kepler-223 system is trapped in an orbital configuration that Jupiter, Saturn, Uranus, and Neptune may have broken from in the early history of the solar system.

“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 & astrophysics at the University of Chicago. “Our work essentially tests a model for planet formation for a type of planet we don’t have in our solar system.”

These puffy, gaseous planets, far more massive than Earth, orbit close to their stars. “That’s why there’s a big debate about how they form, how they got there, and why don’t we have one,” Mills said.

Mills and his collaborators used brightness data from NASA’s Kepler telescope to analyze how the four planets block the starlight and change each other’s orbits, thus inferring 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 the 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 one orbital configuration for far longer.

The planets of Kepler-223 are much larger than Earth, likely consisting of a solid core and an envelope of gas, and they orbit their star in periods ranging from only seven to 19 days. Astronomers call these planets sub-Neptunes. They are the most common type of planets known in the galaxy. 

Kepler-223’s planets also are in resonance. Planets are in resonance when, for example, every time one of them orbits its sun once, the next one goes around twice. Jupiter’s moons, where the phenomenon was discovered, display resonance [as the Talkshop discussed here].

Kepler-223’s two innermost planets are in a 4:3 resonance. The second and third are in a 3:2 resonance. And the third and fourth are in a 4:3 resonance. Astronomers had seen extrasolar systems containing two or three planets in resonance, but not four.

Full phys.org report: Exoplanets’ complex orbital structure points to planetary migration in solar systems

Note: the full report has more discussion on planetary theory.

Comments
  1. oldbrew says:

    They say: ‘Jupiter’s moons, where the phenomenon was discovered, display resonance’.
    True, but we can get an even better comparison by looking at Saturn’s moons.

    Look at the orbital periods of the major Saturnian satellites under ‘Orbital parameters’, here:

    http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturniansatfact.html

    The first four are SI – SIV (Saturn 1 – Saturn 4):
    Mimas (SI) : Tethys (SIII) = 2:1 resonance
    Enceladus (SII) : Dione (SIV) = 2:1 resonance

    This mirrors what we see with the Kepler-223 system:
    c:e = 2:1
    b:d = 2:1

    In both cases the resonance is between non-neighbours, which is itself interesting.

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