COLIN STU­ART AS­TRONOMER AND AU­THOR

BBC Earth (Asia) - - Update -

“All eyes are on the outer So­lar Sys­tem right now. First, astronomers found tan­ta­lis­ing clues of a ninth planet be­yond the or­bit of Nep­tune. But now there might be a tenth, too.

We shouldn’t re­ally be sur­prised. The early So­lar Sys­tem was a much more chaotic place than the largely serene en­vi­ron­ment of to­day. Another planet is thought to have whacked into the Earth to form the Moon, for ex­am­ple. What’s more, com­puter models of So­lar Sys­tem for­ma­tion work bet­ter if there were more than four gas plan­ets to be­gin with. To­day’s gas plan­ets were the grav­i­ta­tional vic­tors in the So­lar Sys­tem’s child­hood squab­bles. Plan­ets Nine and Ten, should they be con­firmed, were likely bul­lied into far-flung or­bits.

But why is it tak­ing un­til now to find them? After all, we’ve found more than 4,000 plan­ets be­yond our So­lar Sys­tem. We don’t spot those ex­o­plan­ets di­rectly – we look for changes in the light from their host stars to in­fer their pres­ence. For us to see a dis­tant planet in our own So­lar Sys­tem, light has to trek from the Sun all the way out there and back to the Earth, fad­ing all the while. So they’re on the edge of what we can seen with cur­rent tele­scopes. With the po­ten­tial Planet Ten, the task is even trick­ier due to its likely po­si­tion close to the bright Milky Way.

Should the plan­ets be found, more than a decade since Pluto was knocked off its plan­e­tary perch, the text­books will need rip­ping up again.”

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