The mystery was finally explained in the 1990s by a massive recalculation of Neptune, but then a new theory, a possible planet nine, was proposed in 2016 by astronomers Konstantin Batygin and Mike Brown at Caltech (California Institute of Technology).

Their theory focuses on the Kuiper Belt, a large belt of dwarf planets, asteroids, and other matter that extends beyond Neptune (and includes Pluto). Many Kuiper Belt objects – also known as Trans-Neptunian objects – have been discovered orbiting the Sun, but like Uranus, they do not do so in a constant, expected direction. Buttagin and Brown argued that something with a greater gravity must be affecting their orbits and suggested Planet Nine as a possible explanation.

This phenomenon will be compared to what happens to our moon. It orbits the Sun every 365.25 days, which is about what you would expect given its distance. However, Earth’s gravity is such that the Moon also orbits the planet every 27 days. From the perspective of an outside observer, the Moon consequently moves in a spiral motion. Similarly, many objects in the Kuiper Belt show signs that the Sun’s gravity has a greater effect on their orbits.

While astronomers and space scientists were initially sceptical about the idea of ​​a new planet, they have since become more convinced by the growing evidence. Growing evidence thanks to increasingly powerful observations that the orbits of trans-Neptunian objects are indeed random. As Brown said in 2024:

“I think it’s highly unlikely that P9 doesn’t exist. There’s no other explanation for the effects we see right now, nor the myriad other P9-induced effects we see in the Solar System.”

In 2018, for example, it was announced that there was a new candidate for a dwarf planet orbiting the Sun, known as ‘2017 OF201’. The object measures about 700 km (about 18 times the size of Earth) and has a highly elliptical orbit. This lack of an almost circular orbit suggests either an impact early in its life around the Sun that put it on this path or a gravitational influence from the nova.

Problems with theory

On the other hand, if Planet Nine exists, why hasn’t anyone found it yet? Some astronomers question whether there is. Sufficient orbital data from Kuiper objects to justify a conclusion about their existence, while offering alternative explanations for their motion, such as the impact ring of rubble or the more fantastic idea of ​​small black holes.

However, the most significant problem is that the outer solar system has not been observed for a long time. For example, object 2017 OF201 has an orbital period of about 24,000 years. Although an object’s orbital path around the Sun can be traced in very few years, any gravitational effects would probably require four to five orbits before any gravitational changes are felt.

New discoveries of objects in the Kuiper Belt also challenge the nova theory. The latest, known as 2023 KQ14, is an object discovered by Subaru binoculars. In Hawaii

It is known as a “Sednoid”, meaning that it spends most of its time far from the Sun, albeit within a large region of the Sun’s gravitational pull (this region is about 5,000 AU, or astronomical units, where 1 AU is the distance from the Earth to the Sun). The object’s classification as a Sednoid also means that Neptune’s gravity has no effect on it.

2023 KQ14’s closest approach to the Sun is about 71 AU, while its furthest point is about 433 AU. In comparison, Neptune is about 30 AU from the Sun. This new object is another one with a very elliptical orbit, but it is more stable than 2017 OF201, suggesting that no large planets, including the hypothetical Planet Nine, are significantly affecting its path. If a nova exists, it would have to be more than 500 AU from the Sun.

This object is the fourth sednoid to be discovered, which is another problem for the planet-nova theory. gave the other three exhibition stable orbits, thus suggesting that any nova would have to be really far away.

However, the possibility remains that there could be a giant planet affecting the orbits of bodies within the Kuiper Belt. But astronomers can only find any such planets with unmanned space travel, which has its limitations. Based on speed estimates, a spacecraft would need 118 years to travel far enough to find it. NASA’s New Horizons The Explorer

This means we have to rely on ground-based and space-based telescopes to detect anything. New asteroids and distant objects are being discovered all the time as our observing abilities become more detailed, gradually revealing what might be out there. So check out this (huge) space, and let’s see what emerges in the coming years.