Call­ing time on Planet Nine

Sky at Night Magazine - - BULLETIN -

Planet Nine may not ex­ist af­ter all. The idea of a ninth planet was in­voked in 2016 to ex­plain the strange be­hav­iour of around 30 7UDQV 1HSWXQLDQ 2EMHFWV 712V %XW D QHZ VWXG\ in­ves­ti­gated whether their own cu­mu­la­tive grav­ity could in­stead be the cul­prit. “If you re­move Planet 1LQH IURP WKH PRGHO and in­stead al­low for lots of small ob­jects scat­tered across a wide area, col­lec­tive at­trac­tions be­tween those ob­jects could just as eas­ily ac­count for the ec­cen­tric or­bits we see in some 712V VD\V $QWUDQLN 6H OLDQ IURP WKH 8QLYHUVLW\ RI &DPEULGJH ZKR co-wrote the study. How­ever, this new the­ory re­quires there to be as much as 100 times more mass in the disc than has cur­rently been ac­counted for. “It’s also pos­si­ble that both things could be WUXH WKHUH FRXOG EH D mas­sive disc and a ninth planet. With the dis­cov­ery of each new 712 ZH JDWKHU PRUH ev­i­dence that might help ex­plain their be­hav­iour,” VD\V 6H OLDQ

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