Caoimhín's Content

Today we are going to bet talking about a planet that is still hypothetical, planet nine or Planet X, the next planet that is yet to be discovered in our solar system, if it exists at all.

Before we get into that, I have made a slight adjustment to the format of my recording. For those of you who watch my videos, you should be able to see the time and date along the bottom of the screen a little bit more clearly in this video than the previous ones. It’s the easiest way for me to show exactly when and at what date I am looking at the sky so hopefully that will make when exactly I’m looking at the sky a little bit more clear in future videos. I do hop through time quickly, but if you pause the video and take a look down at bottom hopefully no part of the time and date will be obscured.

Back to the topic at hand, we are going to be looking far out into space and looking for something that we don’t actually know if it exists. Planet X was first hypothesized as a massive planet out beyond Neptune, and at that time Planet X would have been the ninth planet discovered. Even though X is the Roman numeral for 10, or at least the symbol that we see as a capital X is also used for the Roman numeral 10, it was not intended to mean 10 in this context originally. Numerals and graphemes and all of that are not something I’m going to get into at the moment.

As we’re looking at incredibly distant planets, it is appropriate that we use a dark sky, free of light pollution. Of course we can’t see Uranus or Neptune from the city and we can barely see Uranus with the naked eye even from the countryside but we will push out to the countryside nonetheless. We definitely have no hope of seeing Planet X from the city, and no hope of seeing it with the naked eye at all. Unfortunately, there is no way that this planet is big enough to be visible to the naked eye, it would have to be incredibly large, way bigger than the ice giants Uranus and Neptune for it to be visible from a greater distance than they are. Mars, Jupiter, and Saturn are visible to the naked eye. The planets that are further from the Sun than us that are big enough and close enough, we’ve known about them since at least the Ancient Greeks and most likely even before, they have at least these been written about since Ancient Greek times.

I have mentioned in the past that Uranus may be visible to the naked eye as long as you know where to look, but because of its incredible distance it has an incredibly long orbit, it takes about 84 Earth years for it to get around the Sun once. Uranus take so long to orbit the Sun that it was never discovered in ancient times. Saturn, farther from the Sun than Jupiter, still only takes about 29 Earth years to get around the Sun, Uranus is significantly further and significantly slower moving. It is that slow movement that made it so difficult to ascertain that Uranus was a planet, at least with the naked eye. Once we take a closer look at Uranus we can compare it the background stars and see that it does move. As we move through the near future, Uranus becomes obscured by the light of the Moon, we can see that Uranus and the Moon are going to be very close together in the sky on the 16th of November this year. Regardless, once we’re magnified we can see that Uranus is moving differently to the stars, it is progressing or walking across the sky, it is a planet . We can do the same for Neptune which is out near Saturn in the sky. I know Neptune is out there somewhere because it was pretty close to Saturn the last time we took a look and Neptune takes even longer to get around the Sun, about 164 Earth. years to get around the Sun. Neptune’s incredibly slow orbit means that it takes even longer for us to notice that is moving across the sky, we have to zoom in even closer. Once we do, we can see that, even moving through just days at a time here, it does move but that movement still appears to be pretty slight.

One of the reasons why Neptune was searched for was because of peculiarities in Uranus’s orbit and Neptune’s orbit showed some peculiarities as well. These peculiarities and their indication that another planet may exist still undiscovered beyond Neptune, were observed by Percival Lowell. Lowell was an astronomer, or at least a rich person with an interest in astronomy. Although a graduate of college with a mathematics distinction, Percival Lowell did do astronomy and he founded the Lowell Observatory, which is of course named after him. Percival Lowell did believe that the canyons that we see on Mars were canals created by aliens. This was a very long time ago and of course now we know that that’s in the realm of science fiction, but science fiction and science fact sometimes do blur together. If you try to write sci-fi set far enough in the future, or with rigorous attention to science fact, you might eventually run across something that turns out to be science fact eventually. One famous example is the “communicators” in Star Trek and such and how they inspired the development of the mobile phones that are so ubiquitous today. Percival Lowell was inspired by Camille Flammarion’s science fiction writings about Mars, and even astronomers who are still respected, such as Schiaparelli, believed that canals and intelligent life on Mars existed. Lowell essentially made a mistake, he thought there was canal building aliens on Mars as well. However, once this idea was ridiculed, he wanted to do something to repair his reputation and continue his study of astronomy. There was already good mathematical evidence that Neptune was not the last planet in the Solar System so people started looking. This was in a large part thanks to Percival Lowell, and astronomers at the Lowell Observatory kept searching for the next planet after he passed away. It took very long time, but Pluto was eventually found by Clyde Tombaugh, from Lowell Observatory.

Pluto is a dwarf planet as we understand dwarf planets today. I pleasantly surprised to learn that Pluto is above the horizon before sunset at the moment, though in another couple of weeks it won’t be any longer. Soon it will be too close to the Sun for us to observe, but it is apparently still above the horizon for another little while, so that’s nice. We can take a closer look at easily in simulation, but of course it is tricky to do so in real life. Pluto was discovered because of the search for Planet X, and once discovered it was considered the ninth planet. Planet X was used as a placeholder because it was unknown. For example in algebra, if you are solving for x, x is a variable, it’s an unknown value. Planet X was an unknown planet that could potentially solve the mathematical equation explaining Neptune’s strange orbit, it was never meant to be the Planet 10. However, when Pluto was discovered and Pluto was named the ninth planet, it was seen to be way too small to have any kind of effect on Neptune’s orbit. The large planet, the massive planet that’s big enough to effect Neptune’s orbit, it was still considered unknown. As it would now come after Pluto, it would have been the 10th planet, so Planet X and the Roman numeral X for 10, got conflated, it all got mixed up and mixed together.

We are now back to calling Planet X planet 9. Pluto has been reclassified as a dwarf planet, not a major planet. I am sticking with the definition that dwarf planets are their own thing, major planets are there own thing and that “planets” covers major planets and dwarf planets and minor planets. Unfortunately the language just isn’t super clear and many people consider dwarf planets as planets and all planets are planets. I disagree with that definition because of the confusion that can come from minor planets and minor solar system bodies, then again I’m not in charge and nobody has to listen to what I say. The International Astronomical Union is the one who decides all of these things.

As such, we are looking for another planet that can explain Neptune’s orbit. When people started discovering all of these small objects, they started looking at their orbits. We can use the Solar System Observer to see these orbits, but the issues at hand are not something that I am going to be able to show just by looking at the orbits of these distant bodies. It’s not strictly their orbits or the shape of those orbits that is the issue, it’s their behaviour and their location along these orbits at given times that seems strange. Accidental or coincidental clustering of Kuiper belt and Oort cloud objects is one proposed explanation that doesn’t require the existence of hypothetical other planets, but sheer coincidence isn’t very likely.

The deep solar system objects, sednoids and plutinos and cubewanos, all of these distant things, they do orbit around the Sun. Some of them seem to behave in a slightly strange way, some of them are highly inclined, some of them are highly eccentric. At the moment you might see a hyperbolic, an orbit that’s set to carry something out of the solar system, most likely Comet C/2023 A3. We can see that our asteroid belt as a dense collection of orbits, with our inner solar system inside and our outer objects outside. Beyond the giant planets, we’ve got this big mess of orbits, these truly distant objects. These objects are orbiting the Sun in a way that’s not totally understandable, from the perspective of our current understanding of the solar system and the currently accepted models of physics based on general and special relativity. Our current models don’t explain the behaviour we see. There is a gap in our knowledge, something that we do fully understand about how the small objects at the edge of our solar system behave. One potential explanation is that there is a bigger planet, most likely an Ice Giant, outside these objects that we have yet to discover. The gravity of this object is influencing their orbit, and that’s a perfectly fine explanation. We haven’t found that planet yet, and the longer it goes without us finding that planet, the less likely it is to exist. If it is a sufficiently massive planet, there’s a good chance that we would’ve found it already. However, we don’t know everything about space, we could just looking in the wrong way, it could be highly inclined, it could be very difficult to spot for many reasons.

There are other theories which are in my opinion a little bit more far fetched. One theory is a primordial black hole, that there is a small black hole out at the edge of our solar system. This would have to be a very small black hole and not interacting with a lot of material. With no infalling material it would not generate a accretion disk which would produce light. A small black hole that’s not sucking anything in wouldn’t really be noticeable other than its gravitational effect on the other bodies in the Solar System.

Something else that’s only noticeable through its gravitational effect is the hypothetical dark matter and dark energy. Dark matter and dark energy are not yet fully confirmed, we don’t really know exactly what they are, they’re just a potentially good explanation of how galaxies might work. The way that galaxies move and rotate is also something we still don’t fully understand. Our current understanding of physics fails to accurately predict what we see in the case of these massive galaxies and in the case of the small solar system bodies out at the edge of the Solar System. We do need to keep coming up with theories and potential explanations explaining why our current understanding of physics just isn’t good enough. It’s not that our current understanding of physics is no good, our current understanding of physics is great. It lets us launch rockets into space, and do lots of other amazing things, but we still can’t exactly explain the behaviour of galaxies or the small objects at the edge of our solar system. Maybe it’s dark matter or dark energy, maybe there’s a little black hole orbiting around the Solar System. Maybe it’s just a coincidence. We still don’t know for sure, but we’re still looking, and we’re getting closer. We keep making new discoveries, new hypotheses, getting closer and closer to an accurate prediction of what we see in the sky and the universe around us.

Physics is really just a model, and when we compare that model with the real world, the vast majority of time it works. Physics usually accurately predicts how things in the real world behave, and that’s why we use physics, but there are still a couple of cases where it doesn’t. This is why we need to keep researching, we need to keep learning, we need to keep changing the model of physics that we have until it fits correctly, until we’re able to predict how the universe is behaving and turn out to be right all of the time. We’re right most of the time but not all of the time. Planet X, planet 9, planet next, whatever you’d like to call it, is an artefact, of our poor understanding. It might exist, but we don’t know, we still have to find out. We still have gaps in our knowledge and that’s one of the reasons astronomy and science are so exciting. We still don’t know everything, meaning there is still more for us to learn.

I hope you enjoyed this piece talking about all of that interesting stuff, if you did enjoy then please do like it. If you’d like to support the creation of more content like this then please subscribe to this website and my YouTube channel. Hopefully I’ll see you back here next time.