Is There Another Planet Hiding in the Solar System? | Unveiled

Is There Another Planet Hiding in the Solar System?

There aren’t many things in space that we can be totally certain of… but you’d think we would at least be able to account for all of the closest planets to us. In the twenty-first century, the official line taught all around the world is that there are eight planets in the solar system. The unofficial theories, though, are threatening to change all of that… with mounting ideas that there’s at least one other, lurking undetected.

This is Unveiled, and today we’re answering the extraordinary question; is there another planet hiding in the solar system?

When Pluto was demoted from the top table of planetdom back in 2006, there was a mild uproar in some corners. Ever since its discovery in 1930, this distant world beyond even Neptune had enjoyed solar system status in line with the inner rockies, and the gas and ice giants. For many, it was inconceivable that Pluto could be deemed not a planet. But that’s what happened.

Fast forward to today, and science is much more settled on this idea. We now know a lot more about the Kuiper Belt, where Pluto resides. And we know that it actually contains many more Pluto-like objects. Distant spheres of ice and rock, relatively tiny compared to most of the rest of the solar system planets… but still big enough, in some cases, to carry moons of their own. These so-called dwarf planets have become a major field of study in their own right. But, ironically, by studying them, theories that there’s another, far bigger world out there have resurfaced once again.

Planet Nine. Planet X. Nibiru. The solar system’s lost world has taken a number of names down the years. And, actually, not all theories lead to the same place. Some say that there are unknown planets in the Kuiper Belt, in the Scattered Disc, or even at the inner edge of the Oort Cloud. Others say there’s something hiding closer to the sun, between our star and the first planet, Mercury. Today, we’re looking at one particular theory, though, the story of which starts with Sedna.

90377 Sedna (more commonly known as just… Sedna) is categorised as a large planetoid and an Extreme Trans-Neptunian Object. It was discovered in late 2003, at which time it was deemed to be the most distant place ever observed in the solar system. Currently, it’s about 85 astronomical units (or, AU) away from the sun - which is three times further away than Neptune is, and double what Pluto is. But what most set Sedna apart in the early-2000s was the bizarre nature of its orbit. It travels along an exceptionally elongated route around our star. While the eight standard planets have a mostly circular orbit, with only slight deviations, Sedna’s lap of the solar system is extremely long and flat. As a result, today - despite the incredible distance between us and it - Sedna’s actually a lot closer than it usually is. At its aphelion (its most distant point from the sun), Sedna is 937 AU away. That’s about ninety billion miles. It’s little wonder, then, that it takes more than eleven thousand years for it to complete just one orbit.

Quite apart from the staggering numbers, however, the big question with Sedna has always been why does it move through space in the way that it does? Why does it appear not to be bound by the sun’s gravitational power in the same way that Earth, Mars, Neptune, or any of the other planets are? For some time, it seemed something of an anomaly… but then the mystery took a new shape when we discovered more objects behaving in a similar way.

In 2012, astronomers in Chile discovered another planetoid, officially listed as 2012 VP113 but swiftly renamed Biden (after the then-Vice President of the United States). Biden also has an elongated orbit, stretching between 80 and 436 AU away from the sun. Then, in 2015, a team in Hawaii spotted another object cutting a similar path through the sky. This time nicknamed The Goblin, it’s thought that the furthest point of this one could be more than 2,000 astronomical units away. So, we can see that Sedna is no longer on its own… so much so that these three objects are the first three in a whole new astronomical classification that scientists are calling sednoids. These aren’t cosmic flukes anymore, which means that there has to be a reason for their behaviour. Which is where Planet Nine comes in.

While one explanation for their unexplained, unusual orbits could be that they’ve been affected by a passing star at some point over the last four-and-a-half billion years since our star formed… another is that they’re being pulled in a different direction by a suitably massive planet in the outermost reaches of the solar system. For Planet Nine theorists, this is the Holy Grail. And it makes sense. After all, if the sun were the only gravitational influence on Sedna and the rest, wouldn’t they have a more rounded orbit like the other planets do? Even if they were considerably further out from the centre. If there’s another mass pulling them away, however, their longer orbits seem to check out.

The problem that scientists face, though, is that such a planet shouldn’t exist based on how we currently believe the solar system formed. There shouldn’t be enough mass clumped together, that far away from the sun, to fashion another world out of. So, either the distribution of matter in the solar system doesn’t work as we think it does… or the planet arrived by some other means. There are some theories, for example, that if Planet Nine does exist, it could have once been a rogue planet. It may have once moved through space untethered to anything, until our sun caught hold and whipped it in another direction. Then, there are theories that Planet Nine might not be a planet at all, but a black hole. This would at least explain why, try as we might, we can’t seem to find it.

But, that said, we could now be on the brink of discovery… if there is a discovery to be made. Scientists and astronomers are particularly excited by the Vera C. Rubin Observatory. Named after the astronomer and dark matter pioneer, Vera Rubin, it’s being built in Chile and is scheduled to be fully operational by late 2023. And it’ll become one of the world’s most advanced telescopes, when it does. The Rubin will chiefly maintain a large-scale astronomical survey, in which it will generate a complete image of the sky every three to four days. Scientists will be able to track the movements of solar system objects more precisely than ever before, and too we’re expecting many more objects to be found. If the Rubin works even half as well as we hope it will, then the latter half of the 2020s is set to be a period of immense discovery… and if Planet Nine does exist, there may be no better time for us to finally locate it.

For now, Planet Nine mostly remains fodder for science fiction rather than science fact. At the time of publishing, it’s still a hypothetical world only… with nothing by way of solid evidence that it really is out there. But the theories are gaining weight. At one time, Sedna was an anomaly. A one off, cutting through the solar system in a wholly unique way. But not anymore, and we expect to find more sednoids in the coming years. So, what’s causing their distinct orbital paths? What’s prompting them to move around the sun in a different way? Planet Nine provides at least one solution.

We know that the universe is almost too big to comprehend. But, actually, our star system can be incredibly difficult to get our heads around as well. By current measures, Neptune is the furthest planet out, at about 30 astronomical units from the sun. But, between Neptune and the inner Oort Cloud, there’s at least another 2,000 AU to work with. Sedna (and the sednoids) spend their time here. If you travel to the outer Oort Cloud, though, you’re talking up to 100,000 AU. That’s a lot of space, considering we’re just one star system in just one galaxy. And a lot of room for other planets to potentially move within.

And yet, for the most part, the solar system maintains a balance. It could’ve been chaos, but really it’s quite calm. Most objects move in predictable ways… so when one doesn’t (like Sedna, Biden and the Goblin don’t) it’s potentially very big news. And that’s why there could be another planet hiding in the solar system.