Why Phi? – the three planets of the Kepler-47 circumbinary planet system

Kepler 47 system [Image Credit: NASA/JPL Caltech/T. Pyle]

Astronomers have discovered a third planet in the Kepler-47 system, securing the system’s title as the most interesting of the binary-star worlds, says NASA’s Exoplanet Exploration team.

Using data from NASA’s Kepler space telescope, a team of researchers, led by astronomers at San Diego State University, detected the new Neptune-to-Saturn-size planet orbiting between two previously known planets.

With its three planets orbiting two suns, Kepler-47 is the only known multi-planet circumbinary system. Circumbinary planets are those that orbit two stars.

Continued here.
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Now at the Talkshop let’s take a quick look at the data.

The first two exoplanets found in this system were named ‘b’ and ‘c’ as usual. But recently ‘d’ was spotted in the middle, so in order of distance from the system centre it’s b,d,c.

Anyway, the point here is that the orbit ratio of d:c is 1:1.6180838 (within very small error margins in the data) or 1:Phi (Phi = 1.6180339~, aka the golden ratio).

Another way of putting it is that for every 2.618 orbits of d there is 1.618 orbit of c and 1 (2.618 – 1.618) synodic conjunction in that time period.

These two planets also have a semi-major axis (distance from system centre) ratio of 1:square root of 2 (= 1.414~).

So, a very interesting start to the analysis of multi-planet circumbinary systems – assuming of course that others are found sometime.

Data source: exoplanet.eu [click on ‘3 planets’]

Short NASA animation of the Kepler-47 system can be found here.