A PLANET THAT DOESN’T MAKE SENSE

All About Space - - The Impossible Star -

Ev­ery­thing about ex­o­planet HD 106906 b is un­usual. Not only is it su­per-heavy – 11-times the mass of Jupiter, our So­lar Sys­tem’s heav­i­est planet – it is also ma­rooned in the dark reaches of its stel­lar neigh­bour­hood. It or­bits its star 650-times the dis­tance Earth is from the Sun. Said an­other way, that’s over 16-times the av­er­age Sun-Pluto dis­tance!

Our con­ven­tional mod­els of plan­e­tary for­ma­tion can’t square the pres­ence of such a big planet that far from its host star. Plan­ets are thought to form from a flat disc around a young star. The fur­ther out you travel in the disc, the fewer build­ing blocks there are from which to fash­ion or­bit­ing worlds.

One idea is that it is less of a planet and more of a lit­tle brother. Per­haps a tiny star formed at the same time as its big­ger sib­ling. The trou­ble is that in bi­nary sys­tems the big­ger part­ner is nor­mally no more than ten-times the mass of its com­pan­ion. In the case of HD 106906 b, the size dif­fer­ence is a fac­tor of one hun­dred. How it came to be there re­mains a mys­tery.

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