Astronomers in the US have in­ferred the ex­is­tence of an un­known ‘plan­e­tary mass ob­ject’ af­fect­ing the move­ments of space rocks in a dis­tant as­ter­oid belt

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It seems the So­lar Sys­tem may be a lit­tle more crowded than we thought: a planet around the size of Mars could be hid­den among its outer fringes.

A team from the Univer­sity of Ari­zona has dis­cov­ered a mys­te­ri­ous mass, dubbed Planet Ten, that ap­pears to be tug­ging at the or­bits of a pop­u­la­tion of space rocks known as the Kuiper Belt in the icy out­skirts of the So­lar Sys­tem.

The Kuiper Belt lies beyond the or­bit of Nep­tune and ex­tends to a few hun­dred As­tro­nom­i­cal Units (AU) with one AU rep­re­sent­ing the dis­tance be­tween Earth and the Sun.

The Earth and the other ma­jor plan­ets all or­bit the Sun in roughly the same plane. How­ever, Kuiper Belt Ob­jects (KBOs) are far enough away from the grav­i­ta­tional at­trac­tion of the gas giants to be tilted away from this plane, and are af­fected by in­ter­ac­tions with one an­other.

This an­gle, known as the in­cli­na­tion, can be cal­cu­lated. If the ob­served an­gle dif­fers from the one cal­cu­lated, then it’s pos­si­ble that the smaller KBOs are be­ing pulled out of line by some­thing more mas­sive – po­ten­tially an undis­cov­ered planet. This method is how the ex­is­tence of the so- called Planet Nine was pre­dicted last year.

Af­ter analysing more than 600 ob­jects in the Kuiper Belt, the re­searchers found a dis­crep­ancy of 8° at around 50AU away from the Sun.

“The most likely ex­pla­na­tion for our re­sults is that there is some un­seen mass,” said re­searcher Kat Volk. “Ac­cord­ing to our cal­cu­la­tions, some­thing as mas­sive as Mars would be needed to cause the warp that we mea­sured.”

The re­searchers say we may not have di­rectly ob­served the planet be­cause we haven’t yet searched the en­tire sky for dis­tant ob­jects in the So­lar Sys­tem. How­ever, a chance may come in 2020 when the Large Synop­tic Sur­vey Tele­scope (LSST) is com­pleted.

“We ex­pect LSST to bring the num­ber of ob­served KBOs from cur­rently about 2,000 to 40,000,” re­searcher Renu Mal­ho­tra said. “There are a lot more KBOs out there – we just have not seen them yet. Some of them are too far and dim even for LSST to spot, but be­cause the tele­scope will cover the sky much more com­pre­hen­sively than cur­rent sur­veys, it should be able to de­tect this ob­ject, if it’s out there.”


Artist’s im­pres­sion of Planet Ten

Planet Ten or­bits beyond Nep­tune on a dif­fer­ent plane to the other plan­ets

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