• We don't have pictures of Niku, but here is an artist’s impression of the surface of the distant dwarf planet Makemake. (ESO/L. Calçada/Nick Risinger)Source: ESO/L. Calçada/Nick Risinger
The outer solar system just got a lot weirder.
By
Shannon Hall

Source:
New Scientist
17 Aug 2016 - 10:39 AM  UPDATED 17 Aug 2016 - 10:39 AM

“I hope everyone has buckled their seatbelts because the outer solar system just got a lot weirder.” That’s what Michele Bannister, an astronomer at Queens University, Belfast tweeted last week.

She was referring to the discovery of a TNO or trans-Neptunian object, something which sits beyond Neptune in the outer solar system. This one is 160,000 times fainter than Neptune, which means the icy world could be less than 200 kilometres in diameter. It’s currently above the plane of the solar system and with every passing day, it’s moving upwards – a fact which makes it an oddity.

The TNO orbits in a plane that’s tilted 110 degrees to the plane of the solar system. What’s more, it swings around the sun backwards unlike most of the other objects in the solar system. With this in mind, the team that discovered the TNO nicknamed it “Niku” after the Chinese adjective for rebellious.

To grasp how truly rebellious it is, remember that a flat plane is the signature of a planetary system, as a star-forming gas cloud creates a flat disk of dust and gas around it. “Angular momentum forces everything to have that one spin direction all the same way,” says Bannister. “It’s the same thing with a spinning top, every particle is spinning the same direction.”

That means anything that doesn’t orbit within the plane of the solar system or spins in the opposite direction must have been knocked off course by something else. “It suggests that there’s more going on in the outer solar system than we’re fully aware of,” says Matthew Holman at the Harvard-Smithsonian Center for Astrophysics, part of the team that discovered Niku using the Panoramic Survey Telescope and Rapid Response System 1 Survey (Pan-STARRS 1) on Haleakala, Maui.

And it’s the unknown that excites astronomers. “Whenever you have some feature that you can’t explain in the outer solar system, it’s immensely exciting because it’s in some sense foreshadowing a new development,” says Konstantin Batygin at the California Institute of Technology.

Planet Nine

He should know – Batygin was one of two astronomers who earlier this year announced that the presence of another highly inclined group of objects could be pointing toward a large undiscovered world, perhaps 10 times as massive as Earth, lurking even further away – the so-called Planet Nine.

Upon further analysis, the new TNO appears to be part of another group orbiting in a highly inclined plane, so Holman’s team tested to see if their objects could also be attributed to the gravitational pull of Planet Nine. 

More evidence for Planet Nine as odd celestial alignment emerges
A group of objects with strangely similar orbits is indicating towards a giant, hidden planet in our own solar system backyard.

It turns out Niku is too close to the solar system to be within the suggested world’s sphere of influence, so there must be another explanation. The team also tried to see if an undiscovered dwarf planet, perhaps similar to Pluto, could supply an explanation, but didn’t have any luck. “We don’t know the answer,” says Holman.

Bannister couldn’t be more thrilled. “It’s wonderful that it’s so confusing,” she says. “I’m looking forward to seeing what the theoretical analysists do once they get their hands on this one.”

But Batygin isn’t jumping up and down just yet. “As they say in the paper, what they have right now is a hint,” he says. “If this hint develops into a complete story that would be fantastic.”

Journal reference: arxiv.org/abs/1608.01808

Read these next
Kepler doubles exoplanet population with 1284 new planets
This brings the number of confirmed worlds outside our solar system to over 3200, and we are edging closer to knowing how many are inhabitable.
How Planet Nine may have been exiled to solar system’s edge
It's not yet clear whether there's really a super-Earth travelling an elongated orbit around our Sun
Exploring the solar system: the best of what you can look out for in 2016
From Jupiter to ExoMars to several supermoons, here's astronomer Alan Duffy's guide to the skies this year

This article was originally published in New Scientist© All Rights reserved. Distributed by Tribune Content Agency.