The Most Eccentric Planet Yet

A recent discovery of a new exoplanet has revealed a Jupiter-sized world which whizzes around its parent star as if it were a comet.  The planet, dubbed HD 20782b, is located some 117 light years away, and was discovered initially from the a signal of reflected light as the planet made its closest approach to the star.

The planet has a minimum mass twice that of Jupiter and orbits a star known as HD 20782, which is part of a wide binary star system with HD 20781.  Incredibly, studies of the system showed that the orbit of HD 20782b displays an eccentricity of 0.96, a flattened ellipse which is the most extreme yet to be discovered (1,2).  Yet, the very pace of the perihelion transit this planet experiences as it whips past the star may be its saving grace – it’s is simply moving too fast, the planet’s discoverers think, to be stripped of its atmosphere like many of the so-called ‘hot Jupiter’ class exoplanets.


This planet creates a fascinating precedent for a hypothetical highly eccentric planet such as the mythical ‘Nibiru’.  Of course, the dynamics of the solar system compared with HD 20782 are very different.  HD 20782 is part of a binary star system, where our system is (presumably) not.

“Extrasolar planets like HD 20782 contain a wealth of questions for astronomers, [SF State astronomer Stephen] Kane said. “When we see a planet like this that is in an eccentric orbit, it can be really hard to try and explain how it got that way,” he explained. “It’s kind of like looking at a murder scene, like those people who examine blood spatter patterns on the walls. You know something bad has happened, but you need to figure out what it was that caused it.”

“There are few possible “suspects” in the case of HD 20782, Kane noted. It could be that there was originally more than one planet in the system, and one planet developed an unstable orbit that brought the two planets too close together. This collision or near-collision might have ejected one planet from the system entirely and pushed HD 20782 on its eccentric path. The planet is in a binary star system, so it might also be the case that the second star in the binary made a close approach that threw HD 20782 off a more circular orbit.” (1)

These kind of considerations are not significantly different from those mooted by Zecharia Sitchin for Nibiru, as outlined, he argued, in the Babylonian creation epic Enuma Elish (3).  Catastrophism early in the history of a star system disrupts its smooth flow, potentially perturbing one of its planets into a highly eccentric orbit.


Written by

29th March 2016


1)  SFSU Press Release “Most eccentric planet known flashes astronomers with reflected light” 16th March 2016, with thanks to Lee

2)  Stephen Kane, et al “Evidence for reflected light from the most eccentric exoplanet known” 29th February 2016, accepted for publication in The Astrophysical Journal,

3)  Zecharia Sitchin “The Twelfth Planet” Avon 1976

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