Rebellious Minor Planet Near Neptune Baffles Astronomers
A mysterious object was found near the outskirts of the solar system, and it is behaving quite unexpectedly.
The body is believed to be a trans-Neptunian object (TNO), a term used to describe a minor planet that orbits the sun from a distance beyond Neptune in the outer solar system (Pluto is the first trans-Neptunian object to be discovered).
According to the researchers, Niku, which is a Chinese adjective for rebellious, is behaving quite like the rebel that it is. First, Niku orbits the sun on a plane that is tilted 110 degrees to the solar system's plane, which is the flat orbital disk in which all the planets move around the sun. It orbits slightly above the plane and goes higher before lowering as it orbits back in place.
Second, while all the other objects in the solar system orbit the Sun in the prograde direction, Niku spins around the sun backwards or in retrograde direction.
Niku, which was discovered with the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) in Maui, Hawaii, is not the first trans-Neptunian object with a retrograde orbit. Another object known as 2008 KV42 and nicknamed Drac also has a retrograde orbit, although not with the same orbital tilt.
"It suggests that there's more going on in the outer solar system than we're fully aware of," Matthew Holman from the Harvard-Smithsonian Center for Astrophysics and part of the team that discovered Niku, told New Scientist.
Scientists say that it is extremely unusual for an object in the solar system to have a behavior like Niku's.
"Angular momentum forces everything to have that one spin direction all the same way," Michele Bannister, an astronomer at Queens University in Belfast, said in a report by New Scientist. "It's the same thing with a spinning top, every particle is spinning the same direction."
Scientists suspected that Niku's strange orbit could be a result of a collision with another object in space, or an unknown gravitational force. But the researchers are still unsure about what these objects could be.
Holman's team made further analysis to determine if Niku's unusual angle could be attributed to the existence of Planet Nine - a massive, undiscovered world that is associated with highly inclined objects in the Kuiper belt. But the researchers found that Niku is too close to the center of the solar system to be part of Planet Nine.
"Whenever you have some feature that you can't explain in the outer solar system, it's immensely exciting," Konstantin Batygin from the California Institute of Technology who was part of the group that announced the presence of Planet Nine, told New Scientist. "Because it's in some sense foreshadowing a new development."