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Sun’s lost cousin may be to blame for wonky ecliptic

Tipped over the solar system when planets yet unborn

Earth viewed from space. Image via NASA

Sol may have had a near stellar neighbour at the time earth was formed, and its gravity could be the reason that planets in our solar system don’t orbit neatly around the Sun’s equator.

That’s the thrust of a new letter in Nature, titled A primordial origin for misalignments between stellar spin axes and planetary orbits.

Author Konstantin Batygin contends that as stars often appear in clusters – Alpha Centauri comprises three stars – the disk of matter surrounding a young star and nearly always spreading from its equator could be tugged about by a near stellar neighbour. The gravity of that near neighbour would pull at the star and the disk of matter surrounding it. Once the matter in the disk coagulates into planets they won’t orbit at the host star’s equator.

Earth orbits about seven degrees away from the Sun’s equatorial plane, in what has come to be known as the ecliptic plane. Most of the other planets in the solar system orbit very close to the same plane, excepting recently-demoted Pluto.

Humanity has, to date, observed just one other multi-planet solar system, Kepler 30, and its three planets orbit the star’s equator. But astronomer Josh Winn of MIT likes Batygin’s theory because astronomers have, of late, also spotted gas giants with tilted orbits.

Batygin believes the planet responsible for tugging Earth into its odd orbit is still out there somewhere. So are lots of exoplanets that may prove his theory. ®

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