Pluto - Why isn't it a planet?

This is a question that I've had several people ask me, and one that I've heard discussed numerous times. There is a lot of confusion about -why- Pluto is no longer considered a planet, and no one really went through the trouble of explaining it to the general public. Here is my attempt to spread some truth.

Pluto is no longer a planet because, for a very long time, we had no definition for what a planet really was. Before telescopes were constructed, the planets were Mercury, Venus, Mars, Jupiter, and Saturn. Once we developed telescopes, we discovered Uranus and Neptune and for a while, those were the planets.

However, it was suspected that there was another planet beyond Neptune, because of anomalies in Neptune's orbit. When we were observing it move around the sun, the orbit of Neptune didn't seem to fit what we had predicted, as if there was something else further out in the solar system pulling on it.

This was called 'Planet X', which would explain the anomalies in Neptune's orbit and become the ninth planet. This was the great mistake scientists made that led to Pluto becoming a planet, then being stripped of that status. We didn't find an object and then decide it was a planet. We went looking for a planet and found an object.

There is no large body beyond Neptune. The anomalies in its orbit were found to be because the instruments being used to make the measurements weren't very accurate. Pluto was found by random chance, and even after it was found it was considered odd. It didn't fit into either category of planet.

It wasn't a giant ball of gas like Jupiter, Saturn, Uranus and Neptune. But neither does it really fit in with the terrestrial planets Mercury, Venus, Earth and Mars. Pluto is much less massive than the terrestrial worlds but much more massive than the largest asteroids. Combined with its location far in the outer solar system, it was set apart and somewhat outside our understanding of the structure of the solar system but remained a planet because there was no other classification for it.

The discovery of other objects in the outer solar system complicated the issue. Now Pluto was not an isolated anomaly, but apart of a larger system of Trans-Neptunian Objects. Pluto in particular is apart of the Kuiper Belt, a ring of rocky, icy objects past the orbit of Neptune. If it was the largest object beyond Neptune, it might have remained a planet but there are objects just as big or larger than Pluto, like the dwarf-planet Eris.

That is when the International Astronomical Union (IAU) decided to step in. What they did was to give a somewhat standard definition for what a planet is. In order to be considered a planet, an object has to:

1. Orbit the sun

2. Have enough mass to form itself into a sphere (massive things like Earth have enough gravity that large 'bulges' or bumps get smoothed down, literally crushed by their own weight until the surface is basically a sphere).

3. Have enough gravity to 'clear out' its orbit.

Pluto fails the third requirement. What does that mean?

The eight planets are all massive things. Their gravity is very influential to objects in their immediate area. Take for example Earth. There are no other objects that share an orbit with Earth besides the Moon. Other objects cross Earth's path, but by and large the area around Earth's orbit is empty.

Earth has enough gravity that everything that was in its 'planetary neighborhood' was either pulled in by Earth's gravity or knocked into another orbit. It has cleared out its orbit.

Pluto is in the Kuiper belt. There are objects that share its orbit, and none of them have enough gravity to really clear it out. However, Pluto does satisfy the first two requirements so it is a dwarf planet.

Why did they change it?

The definition created by the IAU is arbitrary, but now at least there is a definition. It was decided that losing Pluto as a planet was acceptable, because any definition that included Pluto would also have to include 44 other objects - all dwarf planets under the current definition. Having eight planets is more palatable to astronomers than 52+. In the end that is what the deciding factor is.

Never accuse astronomers of wanting to memorize things.

Astronomical Intelligence Episode One - Black Hole Formation

Just a quick explanation of how black holes form, and what they are at their core.



The real trick to black holes is wrapping your head around the concept of nothing. More specifically, something being so heavy that it crushes itself. You might have seen where buildings collapse when their foundations are worn away and damaged. That is an adequate description of what happens in a black hole, only the foundations are atoms. Once something is so heavy that it crushes those, then nothing can hold it up anymore, literally. Then it crushes itself to nothing. It's a little hard to conceptualize, as there is nothing on Earth that is similar. But try thinking about this: A trash compactor takes a lot of trash and crushes into a conveniently sized cube. Now imagine that every time it ran the trash compactor crushed the trash into a smaller cube, until finally the trash will be in a single point, like a dot on a piece of paper.

That's basically what happens when a massive star dies. But instead of a hydraulic pistons, it is crushed under the weight of clouds thousands of miles thick, with several times more mass that is in our sun. The core collapses into a single point, and there is enough weight to break apart the very atoms that make up the core of the star. Its like cutting out the support and foundations of a building: there is nothing left holding it up, so the building collapses into nothing.

Except in this case, there is nothing left when the collapse is done.

Before we move on...

Black holes are interesting, but I'm ready to move on so I can cover what I feel like at that moment. I'll deal with one last thing before I go on to something else though.

One thing that many people think when they hear 'black hole' is that if it is a hole, what is at the bottom? A seemingly logical question, and really the fact is that we don't know for sure. We have theories and models that explain what we observe, but we can't actually -test- anything. Any probe or signal we send into a black hole won't ever come out, so we can never really know what goes on at the center.

But lets say you jumped into a black hole to find out what was at the bottom. Would you ever reach a bottom? Could it open into somewhere else?

Both are possible, but really irrelevant. You will never see the bottom of a black hole. Recall earlier that gravity is proportional to the -square- of a distance. Meaning if you are twice as close to something, you experience -four- times the gravity. This means that, amongst other things, your feet are actually being pulled by gravity stronger than your head is, because your feet are closer to the Earth's center of gravity. However, the difference on Earth is so small that it is negligible.

Consider a black hole though, with gravity many times stronger. If you jumped into a black hole feet first, you would slowly begin to feel the gravity at your feet become stronger at your head. This means that your feet would start falling faster than the rest of your body, because gravity is pulling on them more.

You would eventually start to feel stretched as the difference between the gravity at your feet and your head grows stronger. You would slowly start to physically stretch out, your body being ripped apart from the difference in gravity. Eventually you'd stretch into a macabre noodle, as if you were the rope in an astronomical tug of war. This is what we call spaghettification, where your body is pulled into something very much like a spaghetti noodle.

So, who's hungry?

Race to Oblivion

Black holes are formed when the mass of a star is such that when the star finally runs out of fuel that the weight of the star causes the core of the star to collapse. Just like a building collapsing one layer at a time, large stars go through several steps as they desperately try to support themselves. However, unlike a building when the collapse finally reaches the foundation (in the case of a massive star, this is a solid ball of neutrons. One giant atomic nucleus), a star keeps collapsing until there is nothing left. Nothing can support the collapse once it begins.

Electrons are forced to merge with protons to form neutrons.

Neutrons are forced together into a solid mass, until finally they are crushed. With nothing else to support the star, the collapse of the core continues until a black hole is created. All the mass of the core crushed into a singularity, a point that is infinitely small.

The true definition of oblivion.

Black Hole Blowout - Part 1

Black holes are amongst the most misrepresented of all phenomenon in science, both because scientists don't entirely understand Black Holes and because scientists tend to do a bad job of describing what exactly a Black Hole is. Scientists have actually oversimplified the situation in their haste to reduce the huge complexities that black holes represent to something the public can understand, to the point that they are not actually describing black holes anymore.

The standard scientific one-liner to explain Black Holes is generally along the lines of "a black hole is an object which has gravity so strong that not even light can escape it." This is technically accurate, however it implies things that are simply not true.

First and foremost is the idea that black holes have stronger gravity than other objects in the universe, that they act as stellar vacuum cleaners sucking up everything around them. To give an example, imagine this: What would happen if the sun was suddenly and instantly transformed into a black hole of equal mass?

The statement that "black holes are objects that have gravity so strong that not even light can escape them," implies that the planets would get sucked in because the black hole's gravity would be stronger than that of the sun and pull everything into it.

However if the sun was replaced with a black hole of equal mass, the planets would not be sucked into it. In fact, the orbits of the planets would not be affected at all, and the solar system would continue as it always has, albeit much darker and colder without the sun providing energy.

So, a black hole does not possess any more gravitational strength than any other object of equal mass. Yet, it also possesses gravity strong enough to prevent light from escaping. How is this possible? To understand this apparent contradiction, it is necessary to talk about gravity in general.

The attractive force of gravity between two objects is expressed by this equation: Where Fg is "Force of Gravity", M and m are the respective masses of each object, and G is the gravitational constant, a universal constant intrinsic to everything that determines how strong gravity is. Now, r^2 is the distance to between the objects' center of masses.

Now, the center of mass for an object is fairly simple. Lets take the sun as our example.

Now, keep in mind that all matter attracts all other matter individually. What this means is the top of the sun is trying to pull the Earth towards it, while the bottom of the sun is trying to pull the Earth towards it, and so on.

Imagine that every single part (Whether you want to think of regions like top/bottom, or individual atoms) of the sun has its own rope that it is using to pull on the Earth.

Now, think of these 'gravity ropes' as vectors, as in the image below:





The advantage of thinking about gravity in terms of these vectors, at least for the time being, is that it simplifies very well. As you can see, each vector has a horizontal component and a vertical component.

Now, since the sun is (mostly) spherical, there is an equal amount of matter at the top, bottom, left, right, and everything in between. What this means is that the vertical components of these vectors tends to cancel out, like so: This leaves only the horizontal components, which pull the matter directly towards the sun. The center of the sun to be specific, because no matter what direction you move towards the sun, gravity will always pull you directly towards it. The fact that some matter is further away from you is countered by the fact that the same amount of matter is closer to you, giving a center of mass at the center of the object.

So why is this important? As it turns out, in objects like stars or planets, the gravity is strongest at the surface of those object. As you read this, you are feeling the strongest pull that the planet Earth can put on you. If you move away from Earth, you are increasing the distance between you and the Earth's center of mass and the strength of gravity becomes less. But if you move down into the Earth, you are reducing the distance between yourself and the center of mass and so gravity should get stronger right? Remember, that all matter attracts all matter individually. Right now, on the surface of the Earth, all of the matter is pulling you down towards the center of the planet. However, once you are underground, two things change. First, you have less matter pulling you down and second, you have matter above you which will be pulling you up, as this picture shows:


And now we can correct one of the biggest misconceptions about black holes. They possess no more gravity than another object of the same mass. However, black holes are singularities, meaning that you are never 'inside' them. All of the matter is always pulling you down, no matter how close to it you are. The gravity always gets stronger, and this allows something with the same amount of mass to have more powerful gravity effects.

So, describing a black hole as a vacuum cleaner is not accurate. It does not 'suck things in', any more than what other objects do. Rather, black holes are the stereotypical cranky old men that won't let you get basketballs/baseballs out of their yard.

So long as you keep your distance, black holes are no different than any other object. But once you get too close, you never get a chance to learn from that mistake.