Planet Nine: How Could We Miss It?

PLANET 9 It’s four times the size of Earth, only comes along once ev­ery 27 mil­lion years – and yet it is part of our so­lar sys­tem. Planet Nine may be a rare sight, but it’s an ex­tremely pow­er­ful one: when it shows up, it brings with it as­ter­oids that w

World of Knowledge (Australia) - - Contents -

The ter­ri­fy­ing pow­ers of Planet Nine re­vealed

Earth has ex­pe­ri­enced catas­tro­phe af­ter catas­tro­phe. For decades, re­searchers have been tack­ling the thorny is­sue of why, ev­ery 27 mil­lion years, a mass ex­tinc­tion oc­curs on our planet. “It’s a strange phe­nom­e­non,” ex­plains Pro­fes­sor Daniel Whit­mire of the Univer­sity of Louisiana at Lafayette. “Newer re­search shows ev­i­dence of such events dat­ing as far back as 500 mil­lion years.” In re­search cir­cles, the fin­ger of sus­pi­cion points to an undis­cov­ered, ninth planet in our so­lar sys­tem: a phan­tom that turns up to wreak havoc – namely wip­ing out life on Earth – and then dis­ap­pears af­ter­wards. But how could we miss a rogue planet dur­ing 5,000 years of as­tro­nom­i­cal ob­ser­va­tion? And will Planet Nine spell the end for the hu­man race?


The rea­sons why Planet Nine has wended its merry way for so long with­out us notic­ing are sim­ple: “It’s a long way away, re­flects lit­tle sun­light and moves very slowly around the sun,” ex­plains Aus­trian as­tronomer Flo­rian Freis­tet­ter. So you can’t re­ally blame scientists for not dis­cov­er­ing it. Te­le­scopes around the world have scanned the sky for decades, search­ing for any ab­nor­mal­i­ties. And, even if the phan­tom planet hasn’t been spot­ted yet, there are ob­vi­ous clues. If the hunt for who was re­spon­si­ble for these reg­u­lar mass ex­tinc­tions was a court case, Planet Nine would have al­ready been sen­tenced due to over­whelm­ing cir­cum­stan­tial ev­i­dence.

The trail leads to the Kuiper belt: a ring­shaped cloud of as­ter­oids and dwarf plan­ets, or trans-nep­tu­nian objects (TNOS), that pre­vi­ously marked the edge of the so­lar sys­tem. The 13 largest of these ce­les­tial bod­ies are known as ex­treme trans-nep­tu­nian objects (ETNOS) and or­bit el­lip­ti­cally around the sun at a distance of roughly 7.5 to 67 bil­lion kilo­me­tres. How­ever, the fact that they even ex­ist un­der­mines the long-es­tab­lished laws of physics, giv­ing the hun­ters of Planet Nine hope: “They’re kind of in a no man’s land,” ex­plains Scott Shep­pard, an as­tronomer at the Carnegie In­sti­tu­tion for Sci­ence in Washington, D.C. “These objects couldn’t get out there with what we cur­rently know.” No one can ex­plain how they re­tain their or­bits so far away from the sun – un­less a huge phan­tom planet also

“When the so­lar sys­tem was formed, large ce­les­tial bod­ies were flung out from the in­ner re­gion” Flo­rian Freis­tet­ter, As­tronomer

drifts through the empty space be­hind the Kuiper belt, sta­bil­is­ing the 13 out­casts. The reg­u­lar­ity of their or­bits, all of which are at the same an­gle to the sun, is also telling. It’s an­other in­di­ca­tion that Planet Nine ex­ists: nor­mally, the grav­i­ta­tional pull of plan­ets such as Saturn or Nep­tune would disrupt the ETNOS’ route, but that doesn’t hap­pen. In sim­ple terms, this means that, if you take the sun and the eight ma­jor plan­ets of the so­lar sys­tem and ob­serve their in­flu­ence on the 13 ETNOS, the cal­cu­la­tions sim­ply don’t add up – at least not with­out an ad­di­tional fac­tor. How­ever, if you re­place the miss­ing fig­ures in the equa­tion with a ninth planet, or­bit­ing the sun un­ob­served, the be­hav­iour of the 13 ce­les­tial bod­ies sud­denly makes sense. It’s like a pup­pet show: the re­searchers can see the pup­pets danc­ing on stage and even the strings that move them – and as­sume there must be some­thing con­trol­ling them, even if it’s hid­den away. But what does the pup­peteer look like?


To con­struct an as­tro­nom­i­cal pro­file of Planet Nine, re­searchers from the Univer­sity of Bern drew up a phan­tom image of the planet. Us­ing com­puter al­go­rithms, as­tro­physi­cists Es­ther Lin­der and Christoph Mor­dasini were able to sim­u­late the prop­er­ties of Planet Nine, with­out ever hav­ing seen it. “With our study, can­di­date Planet Nine is now more than a sim­ple point mass; it takes shape, hav­ing phys­i­cal prop­er­ties,” ex­plains Mor­dasini. Ac­cord­ing to their cal­cu­la­tions, it’s a gas gi­ant that weights about ten Earths, has a ra­dius of 23,330 kilo­me­tres and a tem­per­a­ture of -226°C. Pro­fes­sor Whit­mire also cre­ated a com­puter model of Planet Nine and found that the rene­gade planet is 100 times fur­ther away from the sun than the Earth. It’s a cru­cial clue be­cause the model fits the mass ex­tinc­tion cul­prit’s pro­file. Whit­mire sug­gests that it takes Planet Nine ex­actly 27 mil­lion years to or­bit the sun, a timescale that co­in­cides with the mass ex­tinc­tions on Earth. And the se­quence of events is clear: ev­ery 27 mil­lion years, Planet Nine ploughs its way through the Kuiper belt, fling­ing as­ter­oids to­wards Earth and re­set­ting life. But the im­pacts aren’t the worst part: ac­cord­ing to re­searchers, the huge cloud of dust they throw up dark­ens the sky for years. An en­counter with Planet Nine would there­fore prob­a­bly be the end of the road for us. But Pro­fes­sor Whit­mire’s the­o­ries con­firm that we’ve still got a bit of time. The next ma­jor mass ex­tinc­tion is not ex­pected to oc­cur for an­other 16 mil­lion years at the ear­li­est.

“We’re be­com­ing in­creas­ingly con­vinced that it does ex­ist” Kon­stantin Baty­gin, Cal­i­for­nia In­sti­tute of Tech­nol­ogy “We are pretty sure there’s a ninth planet out there” MICHAEL BROWN, As­tronomer at the Cal­i­for­nia In­sti­tute of Tech­nol­ogy

OUTER LIM­ITS Scientists have used com­puter mod­els to cal­cu­late the or­bit of Planet Nine. They es­ti­mate that it cir­cles our sun at a distance of up to 225 bil­lion kilo­me­tres. If cor­rect, it means that the so­lar sys­tem is a lot big­ger than pre­vi­ously thoug

PLANET 9 It hasn’t been pos­si­ble to de­tect a ninth planet in our so­lar sys­tem yet, but scientists have found ev­i­dence of its ex­is­tence… OBJECTS WITH SUS­PECT OR­BITS EARTH MASSES OR­BIT LENGTH IN EARTH YEARS 1 1 The or­bital paths of trans-nep­tu­nian objects


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