Retrograde Rock “Niku” Defies the Orbital Trend

The discovery of trans-Neptunian object 2011 KT19 in a strange orbit deepens a key mystery in the outer solar system.
An artist's impression of a distant trans-Neptunian object.NASA  /ESA / G. Bacon (STScl)
This isn't your parents solar system — or even the tidy one you memorized in primary school. In addition to the classic, orderly inner and outer planets, you can now add a bewildering menagerie of Trojans, Centaurs, Kuiper Belt objects, and more.
As a case in point, a recent discov