View Full Version : Niku - an asteroid has astronomers confused

2016-Aug-14, 12:25 PM
ASTRONOMERS are confused by the recent discovery of a mystery object orbiting around the sun backwards. Located in the outer solar system past Neptune, the object was spotted by the Pan-STARRS telescope.


The only problem is it has been moving in an opposite direction to the rest of the planets. This abnormal celestial behaviour has seen the object dubbed Niku the Chinese adjective for rebellious.

Queens University astronomer Michele Bannister said planetary systems are defined by the flat plane of dust and gas surrounding them, with the angular momentum forcing everything to spin the same direction.

Its the same thing with a spinning top, every particle is spinning the same direction, she toldNew Scientist. So the fact the object is moving in the opposite direction to the rest of the planets has Ms Bannister puzzled. Its wonderful that its so confusing, she said. Im looking forward to seeing what the theoretical analysts do once they get their hands on this one.

2016-Aug-14, 04:27 PM
I would guess a close encounter with another massive body, analogous to the best theory for Triton's tightly bound retrograde orbit around Neptune. The other one might well have been ejected in the process.

2016-Aug-14, 05:01 PM
I posted a simulation of this object, as well as 2008 KV42, another steep retrograde TNO on my twitter page:

Nowhere Man
2016-Aug-14, 07:08 PM
Both Niku (2011 KT19) and Drac (2008 KV42) have orbits that are inclined more than 100 degrees to the plane of the ecliptic. Thus, while they are technically retrograde, their orbits are far closer to perpendicular. Which is interesting by itself.

Neither the OP's linked article nor the embedded video mention the orbital inclination. One is left with the impression that Niku is orbiting in the plane of the ecliptic, but going the other way. Tony's simulation does show the extreme inclination.


2016-Aug-14, 07:44 PM
Let me add that Halley's comet has a retrograde orbit inclined about 18 degrees to the ecliptic, so it is not as if we are seeing an unprecedented oddball.

2016-Aug-20, 05:11 PM
A Centaur got jealous of the Ulysses mission...

Roger E. Moore
2018-Aug-08, 06:00 PM

First transneptunian object in polar resonance with Neptune

M.H.M. Morais, F. Namouni
(Submitted on 1 Aug 2017)

Capture in mean motion resonance has been observed in the Solar System for small objects with prograde as well as retrograde orbits of moderate inclinations. However, no example of an object with a nearly polar orbit was known to be in resonance with a planet. In this Letter, we report that the nearly-polar transneptunian object (471325), nicknamed Niku, is in a 7:9 resonance with Neptune, with a mean lifetime in resonance of 16 +- 11 million years. While entrance and exit in the 7:9 resonance is caused by close encounters with Neptune the resonant configuration provides a temporary protection mechanism against disruptive close encounters with this planet. The other nearly polar transneptunian objects do not seem to be in resonance with the planets with the possible exception of 2008 KV42, also known as Drac, that has a small chance of being in the 8:13 resonance with Neptune.