Scientists have discovered two small 'worlds' far outside the orbit of Neptune in the deepest survey ever conducted to search out distant solar system objects.
The new objects are located beyond the Kuiper Belt, which is a region of small icy objects just beyond Neptune, of which Pluto is a member.
They have the third and fourth most-distant perihelia, which is when an object has its closest approach distance to the Sun, of any known solar system objects.
In addition, the orbital motions of these objects are in resonance with Neptune's orbit, which was somewhat unexpected.
Their orbital paths imply that these worlds either have interacted with Neptune in the past or are continuing to do so - despite their great distances from the ice giant planet.
This latest discovery is based on observations made with the Subaru Telescope in Hawai'i and Cerro Tololo Inter-American Observatory (CTIO) telescope in Chile.
Scott S Sheppard from Carnegie Institution for Science and his collaborators Chadwick Trujillo from Gemini Observatory and David J Tholen from the University of Hawai'i have been conducting the widest, deepest survey ever to search out distant solar system objects.
The team members started their survey using the Suprime-Cam imager at the Subaru Telescope several years ago.
Their main goal is to find extreme Trans-Neptunian objects and they already have successfully found several.
Now with the new Hyper Suprime-Cam on Subaru, they are able to cover a lot more of the sky than in the past in their searches for faint distant worlds.
In 2014, the team predicted the existence of a Super-Earth-mass planet orbiting beyond a few hundred astronomical units (AU) away from the Sun.
Its gravitational influence appears to be pushing the extreme Trans-Neptunian objects into similar types of orbits.
The two new objects have very distant perihelia but do not have extreme semi-major axes or eccentricities like the other high-perihelion extreme trans-Neptunian objects (TNOs) such as Sedna and 2012 VP113.
These newly found worlds occupy a region of space just beyond what is known as the "Kuiper Belt edge," which lies about 50 AU from the Sun, researchers said.
Until this most recent discovery, only one object was known to have a low-to-moderate semi-major axis and a perihelion beyond this edge.
The team discovered several more of these objects with high perihelion but moderately eccentric orbits. Their semi-major axes are in the range of about 60 to 100 AUs.
The new objects are all near Neptune Mean Motion Resonances - that is, the locations of their orbits have specific period ratios with respect to that of Neptune.
One of the new objects goes around the Sun once every time Neptune goes around four times, while the other new objects go around once every time Neptune goes around three times.
The research was published in the Astrophysical Journal Letters.
