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Worlds without end: Astronomers detect an exoplanet with an orbit so eccentric that the orbit is more like a comet’s.
The eccentricity of a planet’s orbit is measured on a scale of 0 to 1, with 0 representing a perfectly circular orbit, and figures closer to one indicative of increasingly elliptical orbits. Earth’s orbital eccentricity, for example, is 0.017, and the most eccentric planet in our solar system – Mercury, assuming that we no longer class Pluto a planet – has an eccentricity of 0.205.
Our new friend, HD 20782, on the other hand, has an orbital eccentricity of 0.96, meaning its ellipse as it travels to and from its star is almost flat; and when it does finally return to its sun, after a 597-day orbital journey, it careers furiously round the star to slingshot back into space. “It’s around the mass of Jupiter, but it’s swinging around its star like it’s a comet,” said Dr. Kane.