Planet nine doesn't exist - says a new study

Back in 2016, a hypothesis was introduced which suggested the existence of a possible planet nine. This theory came when scientists observed that there is a huge disturbance in the orbits of some six objects in the outer solar system beyond Neptune. These objects were very much detached from their expected orbits. They were not where they were supposed to be, due to the influence of gravity caused by giant gaseous planets.

Hence, it was assumed that there must be something as large as 5 to 10 times the size of earth, which is situated in the outer solar system, near the kuiper belt, whose gravity is influencing these disturbances. However, no such observation was ever made, to support this hypothesis, and till date, no such planet nine has been discovered.

However, a couple of independent researchers - Antranik A. Sefilian from University of Cambridge in UK and Jihad R. Touma from American University in Beirut, Lebanon - have come up with a new theory that these separation in orbits are caused by several smaller trans-Neptunian objects (TNOs), instead of a single Planet Nine. Although, such a theory was suggested earlier too, but not with calculations. Hence, this is the first time, such a hypothesis is put with calculations, which explain some significant features of these strange orbits while also taking into account the inner eight planets.

With the help of these calculations, scientists were able to create a computer simulation having these unusual orbits with all the eight planets. When they put several smaller objects scattered over a wide area in the kuiper belt, instead of planet nine, they were able to successfully create these orbits. The combined gravitational effect of these smaller objects also explain the inclination and eccentricity of the orbits, which scientists were unable to explain last year.

However, challenge still remains to explain this strange behaviour in the outer solar system, as the current calculations in either of the two models (planet nine or TNOs), suggest that to create such effect, a gravitational pull of several earth masses is required. But, the current estimates put the kuiper belt at only 4 to 10 percent of the earth's mass. But, at the same time, there could be a large ratio of unseen matter in this cluster. Scientists also suggest that there can be a combined model with both smaller objects as well as planet nine.