Transcription
This is Pluto, the ninth planet from the sun. Or at least that's what they told us in school.
But then in 2006, they changed their mind and decided that Pluto wasn't actually a planet anymore and we should all just forget about it. They underestimated us. They underestimated Pluto. And luckily for everyone, a brave group of scientists were undeterred by the assault on Pluto's reputation. And in the same year that our boy was stripped of his planet hood, NASA launched this probe, New Horizons, on a mission to investigate the object formerly known as Planet for the first time up close and personal.
What they found was shocking. We were wrong about Pluto. The people in charge were wrong about Pluto. Everyone had gotten it wrong because it turns out that Pluto is so much more than we ever imagined. This thing might not be a planet, but it is one of the most vibrant and mysterious places in our solar system.
Now, you might be asking, why did Pluto get demoted from its status as ninth planet in the first place? And as much as I want to say that it was a big conspiracy, it really has more to do with a constant change in how we identify objects in the solar system. And this has been going on for longer than you think. For example, back in the 1800s when modern astronomy was really starting to kick off, there were like 20 planets in the solar system because every time someone spotted a new moon or even just a big asteroid, they would declare it a new planet. And at a certain point, this had to be reigned in. So, we started developing pretty strict criteria for what does and does not qualify as a planet. And this has been an ongoing process since then.
In 1930, a self-taught astronomer and telescope maker named Clyde Tomba was hired to investigate the existence of a hypothetical planet X. It was believed that there was something weird out in the distant solar system that was interfering with the orbits of Neptune and Uranus, some yet unknown planet. What Tomba found after 10 months of observation was a faint light moving slowly through space beyond Neptune. He had gone looking for a new planet and by all accounts that's exactly what he found.
Even though the rules had tightened since the 1800s, there were still only two general criteria for planethood in the 1930s. One, the object has to be in orbit around the sun. That's why moons don't count because they orbit planets. And two, the object had to be unique in its location. That's why asteroids don't count. There are a bunch of them all in the same general location that all pretty much look the same. From what we could see at the time, Pluto fit the bill. It appeared to be the only bright object in the distant solar system.
Unfortunately for Pluto, that was not the case. The big change came in 2006 when they updated the planetary definition to say that a planet must have enough mass to clear its orbit of other similarlysized objects. meaning that it needs to be the equivalent of a cosmic vacuum cleaner, absorbing all of the stray rock and dust as it passes by. A planet must be the master of its domain. And as it turns out, Pluto is not just sailing through some distant void out there. It's actually just one object in a massive cloud of stuff that has come to be known as the Kyper belt. It's like the solar systems junkyard. All of the stuff that didn't get pulled in to form the sun, the inner planets or the gas giants ended up in a big ring around the outside. And Pluto isn't even the biggest thing in the Kyper belt. It's just the brightest thing in the area. That's why we saw it first and just assumed it was alone out there.
Turns out Pluto is one of the most highly reflective objects in the solar system. The only planets with a higher reflective index are Venus and Jupiter, mostly because of their dense cloud cover. So, from a distance, Pluto appears much larger than it actually is.
However, Pluto doesn't spend all of its time mixed up in the Kyper Belt. It's actually got a really weird orbit with a very dramatic oval shape that sometimes brings it much closer to the sun than Neptune, coming in pretty much equal to Uranus. And in addition to that, the orbit of Pluto is tilted. Pretty much everything that orbits the sun is on a flat plane, like a disc. But Pluto's orbit is tilted 17° relative to that disc. So it's almost always either above or below us. Not that we'd really notice because it takes Pluto 248 years to orbit the sun.
So because of all that, Pluto is definitely not a planet, but it is weird. And weird stuff can be really cool, which is the reason why the engineers at John Hopkins University built the New Horizon's space probe to see just how weird this could get. And coincidentally, NASA launched New Horizon in the same year that everything changed for Pluto.
The biggest challenge to overcome here was distance. Pluto is very far away and we don't want to wait forever. So, they took this relatively light New Horizon's probe, which only weighed 1,000 lb, and they put it on the most powerful rocket that was available at the time, which was an Atlas 5 that was strapped with an additional five side boosters, delivering around 2 million pounds of thrust. So, New Horizons left the Earth in a hurry. In just 9 hours, it was already sailing past the moon. That's about 10 times faster than the Apollo missions.
After just 1 year in space, the probe is approaching Jupiter. NASA uses this as an opportunity to test out the imaging system. New Horizons takes these photos of Jupiter and its moons, including this shot of an erupting volcano on the moon Io. But the real reason for passing so close to Jupiter is to use the giant planet's gravity as a slingshot to gain even more velocity and push straight on to Pluto.
Now, this is still a long trip. Even with the gravity boost, it takes another 8 years to travel through the outer solar system. As New Horizons closes in on Pluto in 2015, it begins to take the first images. We see these two bright points of light in the distance that start to inch closer and closer as the days go on. That is Pluto and its largest moon, Kiron.
These two have an interesting relationship. Kiron is around half the size of Pluto and it orbits very close, just under 20,000 km away. For context, our own moon is just under 400,000 km out. This close relationship between two similarlysized objects creates a strange kind of tidal locking where only one side of Karon ever faces Pluto just like our moon but also only one side of Pluto ever faces Kon. So if you were standing on the far side of Pluto you would never see the moon and if you were standing on the near side you would always see the moon in the exact same place. Also because Kiron is so big it doesn't actually orbit around Pluto. the center of mass between the two objects ends up somewhere in the middle. So, it appears more like they orbit around a point in empty space. That led some people to theorize that they circled around a mini black hole, but it's just gravity being weird.
However, watching the cosmic ballet of Pluto and Kon was only the beginning. As New Horizons finally closed in, it began taking the first real photographs of Pluto's surface. And this is what it saw. If you were expecting a big blue ball of ice, this is not it. Pluto is a diverse mix of deep red, pale blue, white, yellow, and burnt orange.
The first distinct feature identified in Pluto is this giant pale heart shape. It's created by low-lying planes of ice. And what's really interesting here is that each side of the heart has its own unique character. The side closest to the New Horizon's camera is smooth and flat. We call this area Sputnik Planeteeria. For scale, this is about the size of Texas. And what makes this area so stunning is that it's unmarked by asteroid impact craters, which means that this is a region in constant change. The surface here is active and any blemishes are quickly erased.
Around the top edge of the heart, we see some really interesting patterns emerge. These lines are created by the movement of glaciers down from the highland mountains into the frozen plane. And this tells us that Pluto is not made of ice as we know it. Out here, far away from the sun, the temperature falls to -229°. It is so cold that water ice would be too hard and brittle to form traveling glaciers. So, what we've deduced is that the surface of Pluto is largely made from nitrogen ice. Our own atmosphere is nitrogen-based. It's the majority of the air that you breathe. And you're probably familiar with liquid nitrogen, that bubbling fluid that freezes anything on contact. Now, imagine how cold it would have to be to freeze nitrogen solid. That is Pluto.
Now, if we zoom into Sputnik Planetia, you can start to see these lines in the ice that form a variety of polygon shapes. Those lines are formed by convection currents, which is heat rising up through the surface of Pluto from its core. That heat causes the ice to melt. And only because we're out here in the vacuum of space, it's impossible for liquid to exist, even liquid nitrogen. So, what happens is a process called sublimation, which is when a solid transitions directly to a gas. That gas rises up and actually creates an atmosphere over Pluto. It's not a thick atmosphere. It floats above the surface and forms into layers of thin fog. But it does extend very high up into space because Pluto has pretty minimal gravity to hold it down. The surface pressure on Pluto is probably around 1 million times weaker than on Earth.
Or at least that's the state it was in when New Horizons flew by, which was during the time when Pluto was deep inside the Kyper belt. But we know that it moves on that really weird elliptical path. Though there are times when Pluto is much closer to the sun and during those periods, sublimation will increase and the atmosphere of Pluto could increase to as much as 1/4er that of Earth, which is three times the surface pressure of Mars and might even be enough to allow liquid nitrogen to form on Pluto.
Turning our attention to another eye-catching surface feature of Pluto, that deep blood red stain that runs out from the left side of the heart. This region is commonly known as Cthulhu macula after the cosmic horror of HP Lovecraft. Although the technical name is actually Belin Regio. Either way, what makes it so red? The leading theory is that the color is being made by tholins, which are organic compounds created by radiation from the sun impacting methane and carbon dioxide that is lingering in Pluto's atmosphere. Once those molecules are thoroughly radiated, they clump together, turn red, and fall down to the surface like radioactive snow. And you can see traces of that red splattered across the surface, which helps to illustrate that flow of ice, gas, and potentially liquid that carries the tholins around Pluto.
Now, a less visible but equally as fascinating aspect of Pluto is its giant ice volcano, Wright Mons. The volcano is about 5 km tall and 150 km wide, and it erupts with a slushy mixture of water and methane. This isn't Pluto's only cryo volcano. It's just the biggest, and we don't know how often these erupt, but we do know that the volcanic process here is still relatively active. For as wide as Rightmons is, there's only one visible impact crater on the whole thing. So, we know this is not some ancient structure. It gets refreshed often, or at least relatively often on the cosmic timeline. So, it might erupt every few million years or so.
But where does the slush come from? Well, that's where Pluto gets even more mysterious. You might have been taught in school that this would be planet was just a big ball of ice, but it's not. The evidence collected by New Horizons suggests that the core of Pluto is still hot and that means below the surface there should be a thick layer of liquid water. This is the same composition that we expect to find inside the icy moons of gas giants like Jupiter's Europa and Saturn's Titan. We expect that the heat inside those moons is created by the powerful force of gravity coming from their nearby planet. We don't really have an explanation for where Pluto's heat comes from, though.
In the early years of the solar system, everything was hot. It was like a cosmic dance party with a blazing young star surrounded by a dense cloud of rock and gas and metal that was constantly smashing together and breaking apart and fusing into planets and moons. It was utter chaos. But then everything started to chill out. And as far as we know, smaller objects tend to cool down faster than larger ones. And Pluto is very small and it's out there in a very cold place yet it remains hot on the inside.
And then there's Kiron. This is probably our best explanation for the general strangeness of Pluto. Because they are so similar in size, it doesn't make a whole lot of sense that Kon would have gotten pulled into the orbit of Pluto and stuck there. They probably hit each other at some point in the distant past. And then instead of breaking apart or fusing together, they got caught up in this orbital wrestling match. The energy from that collision and the force of gravity between the two would have injected new life into Pluto. What's interesting is that the distinct heart shape on Pluto is located on the side opposite from Keron. That's probably not a coincidence. And you can see that same deep red tholin deposit on Kon, which is probably caused by ice volcano eruptions on Pluto that are violent enough to escape the weak pull of gravity and spray thins out into space that eventually get pulled in by Kon and build up on its north pole.
Sadly, these images that we've been looking at today will likely be the last photographs taken of Pluto in our lifetime. NASA has turned their attention to closer and more familiar locations in the solar system. Titan, Europa, Venus, and Mars. As a result, there's not even the beginning of a plan for a New Horizons part two. But there is still an amazing journey ahead for the original New Horizons probe. At the speed it was traveling, the encounter with Pluto lasted just a few days before it sailed clean past and headed deeper into the Kyper belt. Remember that Pluto is just the brightest and most visible object out there. But that doesn't mean it's the biggest or even the strangest. New Horizon is out there in uncharted waters finding weird stuff, but that's probably a whole other video.