Our solar system is filled with many unsolved mysteries, one of them being the existence of an icy planet far beyond Neptune. This hypothesised planet nicknamed ‘Planet Nine’ by scientists has gained a lot of attention and speculation since it was first proposed in 2014.
Our solar system is located in one of the spiral arms of the Milky Way galaxy. It consists of eight planets, comets, asteroids and dust. We call this system of astronomical objects the Solar system because all of these objects orbit the Sole (Italian for Sun). In 2006 Pluto was no longer considered as a planet by the International Astronomical Union (IAU) and was instead reclassified as a dwarf planet.
Then, in 2015 two Caltech astronomers, one of whom was involved in the reclassification of Pluto, proposed the existence of a Planet 9. This hypothesis gained a lot of popularity and interest amongst astronomers because it could maybe help explain the anomalous orbits of objects in the Kuiper belt. The gravitational data from the Optical Gravitational Lensing Experiment (OGLE) also suggests that there is something out there that is influencing the orbit of the objects. It has now been named Planet 9 by astronomers and will officially be named once it has been discovered through a telescope.
Scientists used the orbits of certain objects in the Kuiper belt to measure the gravitational force Planet 9 exerts on its neighbouring objects to find out its properties. According to the mathematical modelling, Planet 9 is assumed to be the mass of 10 Earths orbiting 20 times farther away than our Sun on an average. This large orbit of the hypothetical planet means it takes about 10,000-20,000 years to complete one orbit around the Sun making it difficult to observe the planet through a telescope due to its faintness and orbit time.
However, the mathematical modelling done by astronomers has greatly helped make a prediction of its position in the sky. This was made possible due to the long orbit time of the hypothesised planet which allows it to have a constant position in the sky relative to the other eight planets and stars in the night sky. It is believed to be in the direction of the Orion constellation according to calculations and stellar data. Researchers in the past six years have scanned the Southern Hemisphere night sky daily and have identified about 3500 possible candidates for this hypothesised planet. However, to date, none have been confirmed as the one.
There are many theories for what this planet could be and how it was formed. Researchers initially thought it was a small primordial black hole at the edge of the solar system or a rogue planet caught by the Sun’s gravitational field early in during the formation of the solar system. Today, researchers have also started looking at dark energy surveys to see if the presence of dark energy in the galaxy could explain the orbit of objects in the Kuiper belt. Discovering this planet now is crucial to understanding the formation of the Solar System and how planets in general are created.
Regarding the future of finding planet nine, we don’t know what is in store for us. By the end of 2023 a new observatory in Chile called Rubin observatory will be operational. This new telescope will have a new three mirror design which will help create a wide field view and enable astronomers to capture the entire visible night sky in less than four nights. New technology such as this will slowly help eliminate different theories before landing on the one that could explain our current observations.
