Sorry Pluto, We Might Have a Real 9th Planet After All.

Our cosmic backyard is still a mostly undiscovered place. Sure we know of all the major planets that share the same orbital plane as us but discoveries like the dwarf planets in the asteroid and kuiper belts are still recent events. Indeed the more we look at the things that are right next door to us the more it leads us to question just how some of these things came to be. It was the strange orbits of a few kuiper belt objects that led to the most recent discovery: the potential existence of a 9th planet orbiting our sun.

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Why, I hear you ask, if we have a 9th planet have we not come across it before? Well, if confirmed, the reasons for us not seeing this planet before are simple: it’s just too damn far away. Pluto, which was discovered in 1930, is some 7.4 billion kilometers away from the sun at its closest approach whilst Planet 9 (as it is being called) is 5 times that distance at the same point in its orbit. Since planets don’t produce their own light we can only see them when they reflect light of their parent star and, that far out, our sun is a dim speck that barely illuminates anything. That, coupled with the fact that its orbit is perpendicular to ours, makes detection rather difficult and we’ve only found it now due to the effect it’s having on other kuiper belt objects.

The researchers who made the discovery, Konstantin Batygin and Mike Brown (previously credited with the discovery of a dwarf planet, Sedna), were first intrigued by a group of kuiper belt objects that all shared relatively similar orbital properties. Now due to the sheer number of objects that happen to be in the area it’s likely that this will occur by chance sometimes however they often result in unstable orbits. These objects seemed to be quite happy in their strange orbits however so there either had to be a large body, likely a planet, keeping them in line or some other force was at play. In order to verify this one way or the other a planetary model was developed and then simulated to see what other effects a planet might have.

Their simulations predicted that there should also be other kuiper belt objects with orbits that were perpendicular to Planet 9’s orbit. Looking at the data gathered on the numerous objects that exist within the kuiper belt the researchers found 5 objects that matched the simulation’s predictions, a good indicator that a planet is responsible for both them and the other peculiar orbits. This also helped to confirm some attributes of the planet like it’s potential mass (10 times that of earth) and its likely orbital period (10,000+ years). Interestingly enough this helps to fill in a gap in our solar system’s construction as current models predict the most common type of planet is one of Planet 9’s mass.

The researchers are now looking to directly image the planet in order to confirm that it exists. There’s potential for it to show up in data already collected however that will only work if it was currently close to the sun. If it was further out then time will be required on some of the larger ground based or potentially one of the space based telescopes in order to observe it. Either way direct confirmation is some way off but is surely forthcoming.

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