In the 1980s, space scientists and astronomers started talking about the existence of a new planet (called Planet X) to explain certain phenomena, such as the unexplained residuals in the orbit of Neptune. As new discoveries emerged over time, the idea gradually evolved and this hypothetical entity came to be known as Planet Nine – a large planet beyond Neptune in the outer region of the Solar System.

Specific theories for Planet Nine’s existence started around 2014 when some scientists witnessed the inexplicable clustering of orbits of Extreme Trans-Neptunian Objects (ETNOs). They argued that this complex phenomenon could be the result of the gravitational influence of a huge planet that possessed 5x-10x of Earth’s mass. However, other scientists postulated that the Dark Energy Survey (DES) data did not provide any robust evidence of this strange clustering, and rejected the idea of a new planet. Some also opined that this strange orbital clustering could be due to the collective gravitational influence of the numerous small objects that are scattered around that part of our solar system.

New evidence now suggests that Planet Nine may have already been observed in the 1980s. Recent analysis of past data from the decommissioned Infrared Astronomical Satellite (IRAS) suggests the presence of a massive body that orbits around the sun around the same location as the proposed Planet Nine. While it is still not fully clear whether this entity is actually a planet, some scientists suggest that the data indicates that it is a moving body, much like a planet. This observation has again ignited the conversation on Planet Nine’s existence.

Acknowledgement: https://arxiv.org/abs/2111.03831