The far reaches of the solar system constitute a dim and distant realm, with details that are challenging to grasp. Due to the diminished sunlight away from the sun, even a relatively large planet can easily elude our notice.
Scientists have observed some peculiar clustering behavior among Trans-Neptunian Objects (TNOs) beyond the orbit of Neptune, hinting at the presence of a hidden world.
This has led scientists to propose the idea of a ninth major planet, a large Earth-like planet lurking beyond our visible range. Now, two scientists present an alternative explanation: a more modest, Earth-like world closer than the controversial ninth planet, situated on an inclined orbit, explaining the peculiar behaviors due to the existence of something larger.
According to planetary scientists Patrick Sofia Lecarca from Kinki University in Japan and Takashi Ito from the National Astronomical Observatory of Japan, this frozen and dark world, far from the sun, would not exceed three times the mass of Earth and would not orbit beyond 500 astronomical units. They state, "We predict the existence of an Earth-like planet and several TNOs on special orbits outside the solar system, which can serve as observable verification signals for the assumed planet's perturbation."
The most distant object discovered in the solar system, when found, was 132 astronomical units from the sun. In comparison, Pluto's average distance from the sun is about 40 astronomical units. Beyond Neptune (30 astronomical units from the sun), there is a vast collection of icy rocks and dwarf planets extending beyond our visible range. This is the Kuiper Belt, containing objects known as Trans-Neptunian Objects (TNOs).
In recent years, with more sensitive telescopes and surveys, scientists have discovered more TNOs than previously known, leading them to notice patterns. One such pattern is clustering, where some TNOs cluster and move on inclined orbits, suggesting that they are influenced by the gravitational pull of much larger objects than the smaller ones we have discovered so far.
In 2016, astronomers Mike Brown and Konstantin Batygin from the California Institute of Technology pointed to a hypothetical ninth planet as the culprit. This planet was estimated to be approximately 6.3 times the mass of Earth, with an orbit exceeding 460 astronomical units. However, they were not the first to propose an explanation. Patrick Sofia Lecarca and colleagues noticed TNO clusters in 2008 and put forth the hypothesis of a hidden Kuiper Belt planet.
Now, with more data, Patrick Sofia Lecarca revisits this idea and refines it. They identified characteristics of a hypothetical planet that could explain some features of the Kuiper Belt. Further observations can confirm if they are correct.
They write, "We determine that an Earth-like planet on a distant and inclined orbit can explain three basic characteristics of the distant Kuiper Belt: a large group of TNOs beyond Neptune's gravitational influence, a large group of high-inclination bodies, and the existence of some extreme objects with special orbits." This Earth-like planet's mass would be between 1.5 to 3 times that of Earth, and its farthest point from the sun would be between 250 to 500 astronomical units, with an inclination of 30 degrees relative to the plane of the solar system.
Its presence could explain objects with inclinations greater than 45 degrees and the orbits of objects like the dwarf planet Sedna, which has an unusually peculiar and elongated orbit. It could also account for characteristics seemingly related to Neptune's outer trans-Neptunian object group, typically excluded from such studies.
The findings of Patrick Sofia Lecarca and Takashi Ito provide testable features for their assumed planet. The gravity of this planet would aggregate Trans-Neptunian Objects beyond Neptune into a cluster beyond 150 astronomical units, and with advancements in technology and instruments, we may be able to detect these objects.
They state, "A more detailed understanding of the remote Kuiper Belt orbital structure can reveal or rule out the presence of any hypothetical planets in the outer solar system. The existence of a Kuiper Belt planet may also provide new constraints on planetary formation and the dynamic evolution of the trans-Jupiter region."
