The Planets and Pluto

There are 7 other planets in the solar system (Pluto is probably not a planet, and there are very good reasons why). Each one is profoundly unique, with features and wonders which you cannot find on Earth. Some may contain life. But sometimes we forget that there are planets other than Earth and Mars, and that doesn’t make them any less fascinating- it’s simply because we are so technologically backwards that we can only barely manage to explore one other planet. There are worlds which astronauts would dream to set foot on, but can’t due to a huge array of physical challenges. Extreme heat and extreme cold (sometimes on the same planet, even in the same spot on the same planet within a few hours), extreme gravity, toxic gases, electrical storms, overactive volcanoes, bombardment by asteroids, and massive, icy geysers are just a few. But that doesn’t mean that we should just let them be. Many of these worlds have HUGE amounts of valuable raw materials which we only find in trace amounts here on Earth. Which we have to strip mine and extract using methods which are damaging to the environment and to our own health. Space exploration is the single most important, fruitful, and inspiring endeavour we can embark on.

Here is a chart of basic stats regarding all of the 8 planets and Pluto. For those who have no astronomy background, a day is the amount of time it takes for a planet to rotate 360 degrees, all the way around, and a year is how long it takes to complete one orbit around the sun (I sense eye-rolls, but not everybody knows this and the implications for science fiction and hopefully actual space travel often go ignored. How do you think the body would react if night lasted 50 days, or if a single frigid/scalding season lasted a century? How difficult would it be to colonize a world with even slightly more or less daylight, how would that mess with our biological clocks? Sure the native life would be naturally adapted to such things, but we sure wouldn’t. Would artificial light and shade be enough to keep our internal hormones balanced? And if so, could it last potentially an entire individual’s lifetime?).

A simple, ugly chart of basic planet characteristics

A simple, ugly chart of basic planet characteristics

Mercury

Mercury, the smallest planet and the closest to the sun

Mercury, the smallest planet and the closest to the sun

Mercury’s surface gets to scorching temperatures. 427 degrees Celsius is enough to liquefy zinc. At it’s coldest, the temperature is almost enough to liquefy oxygen. There is some seriously strange stuff going on here. Logic dictates that the further away from the sun a planet resides, the colder it will be. But Mercury, the planet closest to the sun, is sometimes colder than Earth! In fact, it gets colder than both Jupiter and Saturn, and approaches the temperatures of Uranus and Neptune. The fact that something can be that close to the sun and still be twice as cold as Antarctica is astounding. There are two reasons for this.

Mercury has almost no atmosphere. It is just a hunk of rock floating in space, no more than a large asteroid. The little atmosphere that it possesses is actually just debris that has been vaporized by the sun and scatters into space as Mercury whizzes by. And it really does whiz by- Mercury orbits the sun in a period of just 88 days, which is due both its tiny orbital radius and the fact that it travels faster than any other planet.

But perhaps the most interesting aspect of mercury is its day. In an entire Mercurian year, the planet revolves exactly 3/2 times- or three times for every two orbits. This means that any given point will be facing the emptiness of space for 59 days, which is the other reason why it gets so cold. But what this illustrates is a planet’s remarkable capacity for insulation. Mercury is a tiny planet, about 5% of Earth’s total volume. For reference, it has a total surface area marginally higher than the Indian Ocean. And yet, the planet lies a little more than a third of the distance between the sun and Earth. This means that there is enough rock separating the cold surface from the sun to shield it from most of the radiation. Planets are the Universe’s thermoses.

Venus

Venus, the hottest planet in our solar system

Venus, the hottest planet in our solar system

Perhaps the most Earthlike planet in the solar system, and that includes Mars. Venus is similar in size to the Earth, closer in fact than any other planet. It is also the hottest planet in the Solar system.

Hotter than Mercury? By far. Venus is the polar opposite of Mercury, in that it has an extremely thick, dense atmosphere that traps ridiculous amounts of heat. Notice that there is virtually no temperature variation. That is because the atmosphere is thick enough to trap enormous amounts of energy for 243 days, while a point on its surface is pointed away from the sun. We already talked about the incredible insulating powers of planets, and although Venus’s far side gets no sunlight for four times as long as Mercury, it is still able to retain its heat almost completely.

The most fascinating, terrifying aspect of Venus’s atmosphere is its composition. It is mainly carbon dioxide with clouds of sulfuric acid. If that sounds familiar, wait for it- it is likely that Venus became hell incarnate through a runaway greenhouse effect. It is possible that increasing amounts of CO2 in the air triggered a feedback loop and Venus heated up like a bowl of soup in a microwave.

But the point of no return was when its surface water evaporated. Excessive amounts of water vapour is one of the worst greenhouse gases. Once that happened, the heating increased exponentially until the surface was completely cooked and inhospitable. And after all its water was in the air, the sun dragged it out and whirled it into space. Now there is hardly any water left in Venus’s atmosphere, circling what was once a planet theorized to be hospitable, like Earth.

It takes a long time for this greenhouse effect to get to the point of Venus- billions of years, and not the hundreds it would take to wipe us out. But eventually our artificially induced greenhouse effect would lead to the same thing.

Other than its cheerful atmosphere, Venus is also the only planet to rotate backwards. As in, the sun rises in the west and sets in the east. No one really knows why, but it may be due to the extreme tidal effects of the sun on its atmosphere.

Earth

Earth, the home of every known living thing in the Universe

Earth, the home of every known living thing in the Universe

Our home, the only place that the vast majority of human beings have ever been. The Earth is situated within the Sun’s habitable zone (along with Venus and Mars), the area around a star which is within the temperature range to support life as we know it.

This is also the first planet to have a moon. A moon is just an object that naturally orbits a planet. You can think of the planets themselves as the moons of the sun. The only difference between a moon and a planet is that moons orbit planets while planets orbit the sun.

The Earth has an immensely hot core, hotter than the surface of the sun. At anywhere from 5000-6000 degrees Celsius, it is hot enough to melt almost every known metal, enough to even boil most metals. It is thought to be composed of mostly iron, nickel, and precious, dense metals like gold and platinum. In fact it is theorized that there is enough gold in the core to plate the entire surface.

Where on Earth did this enormous heat reservoir come from (please forgive me)? It is thought that the radioactive decay of uranium and thorium, which releases immense amounts of energy, is what provides the fuel. This is actually how nuclear power plants work, so in essence the Earth’s core is the most sophisticated, largest nuclear furnace we have access to. All tectonic activity on the planet is a side effect of the massive amount of heat given off by radioactive decay. Think about how amazing that is- the continent you’re sitting on is moving on the farts of a nuclear reactor hundreds of thousands of miles below your feet.

But the Earth’s ability to support life is what separates this planet from the rest. The precise conditions for life to exist not only had to come into being, they had to maintain their state for 3.6 billion years. It took 2.6 billion years to go from single cells to multicellular life, and another billion to go from there to humans. Which is remarkable- it took 2 and a half billion years for cells to figure out how to work together. And we think humans are uncooperative. But after that, it was only a billion years to go from a handful of cells to the immensely complex entities that we are, and it only took a few thousand years to go from surviving to building skyscrapers. More than anything, the story of life represents the unfathomable power of cooperation.

Mars

Mars, the red planet and the most well studied extraterrestrial body

Mars, the red planet and the most well studied extraterrestrial body

The red planet is named after its rich iron content, which makes it appear so. Mars is the closest planet to Earth in terms of living quality. The reason why finding life on Mars is so important is because it will force us to rethink our place in the Universe. If life is capable of existing in two places in the solar system, then there is no reason to assume that other star systems (and there are trillions of them) don’t also have life. Likely even intelligent life.

Mars is the second smallest planet, and the last of the terrestrial planets (the first four planets are terrestrial, or rock planets while the last four are gas giants). It once had large reservoirs of liquid water, like Venus, but unlike the greenhouse world it still contains large amounts in the form of ice. This makes exploration and possible colonization a thousand times easier. Water is heavy, fuel is precious, and transporting enough water for a reasonably large team of astronauts to survive is the single biggest challenge of manned space exploration. It’s why we’ve only ever sent rovers to the surface, and why the harvesting water from the ice (or other undiscovered reservoirs) is imperative for an expedition. There is a colonization project, Mars One, which aims to put humans on Mars by 2024. Whether it will succeed remains to be seen, but the fact that we are trying is magnificent.

Mars also has a very thin atmosphere, which is why there is no liquid water on the surface. It simply evaporates before it can collect. But Mars has huge terraformable potential (the ability to turn an inhabitable planet into a habitable one). It simply needs greenhouse gases in order to give its atmosphere a boost. In fact, one proposed solution to climate change is to collect the excess carbon dioxide, store it, and transport it to Mars where it will actually make the planet liveable. It takes a huge amount of resources and energy however, more than we can afford to spend with our current levels of technology. Just imagine, though, if we could do that. Two birds with one stone- the solution to climate change and the colonization of another planet, more space for a rapidly increasing population and another place for new cultures to develop.

Jupiter

Jupiter, the largest planet in our solar system.

Jupiter, the largest planet in our solar system.

Jupiter is the first of what we call the gas giants- simply because they are mostly made up of gas. Jupiter is more than twice as large as all of the other planets combined. The size of this planet produces some neat effects. There is so much hydrogen and so much gravity that these layers of gas are compressed. They are squished together so tightly that some of these layers can conduct electricity (basically, they are no longer gas, they are plasma). The gravity is so intense that Jupiter is actually a heat source– it radiates more than 1.5 times the energy it receives from the sun. This is because the gas gets squished together at such extreme pressures that the friction alone is enough to create enormous amounts of energy. If Jupiter were a few times bigger, its gravity would be strong enough to heat up its core above three million degrees Celsius. That is hot enough to start hydrogen fusion, which is how the Sun produces energy. Essentially, if Jupiter were any bigger it would be a star.

Being a gas giant makes a planet have no solid surface to step on. We could never set foot on Jupiter because there is nothing to set foot on. The entire planet is one gigantic atmosphere. It’s not the atmosphere, or the gravity that would kill us first, however. The magnetic field is so powerful that it would fry us if we even got close.

No discussion of Jupiter would be complete without mentioning the Great Red Spot. Any picture you see of Jupiter will have it, a glaring red eye that twists several of its layers together. The spot is the largest storm in the solar system. It is larger than three Earths and has been going on for 350 years. Which in itself, is really cool because we’ve learned to associate the Great Red Spot with Jupiter itself. It predates the telescope. If we made telescopes a few hundred years earlier, then Jupiter would look completely different. Try googling a picture of Jupiter without the spot- almost every image we’ve taken has it included. It is part of our idea of Jupiter, and yet in the scale of the cosmos it is fleeting.

But an exploration of Jupiter isn’t nearly as useful as an exploration of its moons. Jupiter has 67 moons, of which 4 are worth talking about. Ganymede, Callisto, Io, and Europa. Ganymede, Europa, and Callisto have tons of ice covering them, as well as underground oceans. Ganymede and Europa also have atmospheres of oxygen, which make them more ideal for exploration than Mars. Combined with the fact that like Earth, they have molten cores, means that they have at least two of the necessary ingredients for life as we know it- water and heat. Unfortunately, these oceans are buried beneath miles of rock, and seeing as no one really cares about space and that we’ve barely dug through our own crust, investigating whether life exists in these massive underground oceans is probably not going to happen within our lifetimes, which is a huge shame.

Io has the most volatile geology of any object in our solar system. It is completely covered in volcanoes that spew bursts of lava and sulfur dioxide that makes the volcano that buried Pompeii look like a firecracker. These gases react with Jupiter’s magnetic field, and combined with the ionized gases of Jupiter’s own atmosphere, form a sheet of pure plasma around Jupiter’s equator.

The four Galilean satellites of Jupiter

On a sidenote, dabblers in Greek mythology will notice that these four moons are named after Zeus’s love interests (whose Roman name is Jupiter). Ganymede is a man. Zeus was not picky. These were all discovered and named by Galileo himself, who made the executive decision to name the largest moon Ganymede. Considering the Catholic Church’s fondness for homosexuality, I do not think that this helped his case when he was placed under house arrest for a large chunk of his life for ‘heresy’.

Saturn

Saturn, famous for its massive rings

Saturn, famous for its massive rings

Saturn is my favourite planet, hence its place as this website’s header. It is the second largest planet in the solar system, of similar composition to Jupiter, and yet there are several things that make it stand out. First and most obvious is its rings. These are not solid disks as they appear, but tons of little ice moonlets that whiz around the planet in organized patterns, which the website’s header image does an incredible job of capturing. The distance between the inner ring and the outer edge is 114000 km, which is almost three times the circumference of Earth. And yet, the disk is about 20 metres thick.

That seems like a lot. 20 metres is not an insignificant height. But when you consider how wide the sheet is, it’s less than paper thin. Seeing that from close up would be a sight that nothing on Earth could match. Just imagine floating just outside Saturn’s orbit, seeing a gigantic luminous ball of gas surrounded by a vast ring structure, more than several times the Earth’s size in width and encircling a total area that is beyond our comprehension.

The rings of Saturn. How anyone could not want to see this in real time is beyond me.

The rings of Saturn. How anyone could not want to see this in real time is beyond me.

The rings and gaps are in quite precise arrangements. But no one really knows why Saturn has such massive rings. One of its moons, Enceladus, has ice volcanoes which shoot ice out of the moon’s atmosphere. Over time, these pieces could have aggregated around Saturn’s equator, growing to massive size over hundreds of millions of years (that is not actually that long. If a particularly ancient dinosaur were to look up at Saturn through a telescope, there would be no rings to see).

One of the coolest things about this planet, that is not widely known, is the fact that it radiates light and heat. Jupiter does too, at about one and a half times the amount of energy that it receives from the Sun. But Saturn radiates over twice the energy received. Which does not make any sense, because the reason why Jupiter produces so much energy is that its enormous gravity causes so much friction that the planet lights up like… well… a lightbulb. Saturn is a fraction of Jupiter’s size, and yet it radiates proportionally more energy. A lot more. And the fact that there is a gigantic flashlight sitting on our cosmological doorstep, and that we have no idea why it produces so much energy, is seriously awesome.

And then there are its auroras. Saturn has auroras that are bigger than our entire planet. These electrical displays can be seen through a telescope, taking up a significant portion of Saturn’s surface area.

Look at that. That dances and flashes different colours, sometimes flaring up. As far as tourism goes, I want to go here.

Look at that. That dances and flashes different colours, sometimes flaring up. As far as tourism goes, I want to go here.

Saturn, like Jupiter has about 60 moons. We’ve already discussed Enceladus’s ice volcanoes, but it also has a recently discovered underground ocean of liquid water, as I talk about in Otherworldly Oceans. Titan, however, is the coolest cat of all the moons in our solar system.

It is the only moon to have a significant atmosphere, comparable to an actual planet. For a long time, no one knew what was on Titan’s surface, but what we found was super interesting. It has lakes of hydrocarbons, which are the foundation of all life on Earth. That’s like having lakes of oil on the surface of Earth. Literally the perfect refueling station for any expeditions into space. It also has liquid and ice water, another aspect of the ideal refueling station.

And then there is the atmosphere itself, composed of nitrogen and methane. In fact, it is rich enough to have seasonal weather patterns, wind and rain that is very similar to that on Earth. Only instead of a water cycle, it has a methane cycle. Scientists have often proposed that Titan could very well harbour life- but it would be like nothing on Earth. This separates it from the other life hotspots in the solar system. Instead of water, life would use liquid methane. It would still use hydrocarbons, but the shapes of its genetic material and cell walls would be totally different. It might not even use cells as its substructure. It could be so far off from what we know that we can’t even comprehend how weird it is until we see it. If we found life on Titan, it would signal a new age of understanding on our planet, because it would prove that there is more than one way for life to evolve, and that the ingredients that led to life on Earth are not actually necessary.

Titan, which mirrors Earth in terms of its atmosphere

Titan, which mirrors Earth in terms of its atmosphere

Uranus

Uranus, the most hilariously named planet in the solar system

To be fair, Uranus is not pronounced how you think it is, and is named after the Greek god of the sky. But the story of the naming of Uranus smells funny. When it was discovered in 1846, William Herschel, who discovered the planet, got to name it. He chose Georgium sidus. This was not very popular because no one outside of Britain wanted the newest planet to be named after a British king. Some suggested Neptune, to commemorate Britain’s naval victories, but of course the same problem arose. Then Johann Elert Bode proposed Uranus, the Latin version of the Greek god of the sky, Ouranos. The justification was that as Saturn was the father of Jupiter, Ouranos was the father of Saturn. The name quickly caught on and public favour cemented it as its official name.

However I choose to believe that people of the time are just as immature as we are. Anyone familiar with Roman mythology knows that Roman gods are just Greek gods with new names. All of the planets are named after Roman gods, and the Roman name for Ouranos is Caelus in Roman mythology. Why not name the planet Caelus? And if there was some good reason for choosing the Greek variant over the Roman (there isn’t), then why not choose Ouranos? Why go with the Latin version? There is no way that the hilarity of the name simply went unnoticed. Anus was a word in regular use at the time, and it is important to remember that it was the fact that the name caught on with the general public that led to it becoming the official name. I believe that Johann Bode’s arbitrary justification for the name was just a way to get it past the stiff necked, overly formal customs of the time. It makes me extremely happy that he got away with it.

Uranus is a cold-ass planet (I’m sorry but I’m never not going to find this funny. Prepare yourself for grade school levels of immaturity. If you are of a more stoic nature, I suggest you go to Wikipedia). At ~-200 degrees Celsius, it is the temperature at which nitrogen naturally becomes a liquid. Like Jupiter and Saturn, it contains a lot of hydrogen and helium, but it also contains more complex gases. Specifically methane, which is also the gas that is expounded from its homograph, and ammonia. I don’t believe that the fact that Uranus has more fart gas than the other gas giants is a coincidence.

Uranus also has incredible wind speeds (I seriously think the Universe planned this joke). The fastest wind speed ever recorded on Earth is 408 km/h. On Uranus, they can reach speeds of 900 km/h. When you consider the destructive power of wind on Earth, having the capacity to hurl trucks and buildings through the air, wind speeds more than twice our maximum are enough to rip anything we sent to Uranus’s atmosphere to atomic shreds. It will be a long time before we send anything to explore this planet.

Its axis of rotation is parallel to the equator. Basically it rotates sideways, unlike any other planet in our solar system. It also has two sets of rings. These ring systems are quite small (one was only discovered in 2003), and are thought to be the result of a collision between two or more of Uranus’s moons.

Uranus has at least 27 moons, all of which are named after characters from Shakespeare and Pope. Most are made of rock and ice.

Neptune

 

Neptune, the farthest planet from the sun

Neptune, the farthest planet from the sun

Upon Neptune’s discovery, naming tradition went back to Roman gods. Further evidence that points to the fact that Uranus’s name is not a coincidence. Neptune’s discovery is unique, because it represents a shift in science as a whole. All of the other planets were discovered by observing the night sky, either with the naked eye or by poking around with a telescope. Neptune’s existence was predicted before it was ever discovered, highlighting an important facet of science that separates it from all other disciplines- scientific theories can make predictions, which if they come true, lend evidence to their veracity.

Enter Issac Newton. He formulates his laws of motion and the law of universal gravitation which explains why the moon rotates around the Earth and the planets rotate around the sun. However, gravity weakens exponentially with distance. Since the sun is so massive, the planets must orbit the sun rather than each other. But Uranus and Neptune are really far away from the sun. They are still held in orbit, but the path of Uranus is not a perfect circle. Astronomers realized that it was being pulled by something else.

So they used Newton’s laws to their fullest potential, mapping the orbit of Uranus and seeing the directions in which it was pulled. They calculated that if gravity was the only force that had any effect on Uranus’s orbit, then there had to be another planet of similar size a little further out in space. Space is vast, and finding Neptune by chance is extremely unlikely. Using only mathematics, they calculated the precise size of Neptune, how far it was from the sun, and even mapped out its entire orbit. They calculated where they thought it would be.

Except that this was not a collaboration of astronomers and mathematicians. This was an intense rivalry, made even more so by the complexity and difficulty of the task. The two in question, John Couch Adams and Urban Le Verrier, raced to calculate the position of this new world.

Le Verrier had better calculations, but Adams had better connections. He had less trouble in getting astronomers to actually look for the planet. When Adams’ boss saw that Le Verrier’s calculated position was similar to Adams’, he used his influence to speed up the search. Le Verrier had to mail Berlin to get them interested. However it was too late, and on the night that Le Verrier’s letter was received, the discovery was made by Adams’ boss’s contact.

Of course, because one was French and the other was British, there was a huge nationalistic issue over who got credit. The planet was discovered much closer to Le Verrier’s predicted position than Adams’, but it was through Adams’ contacts that it was found. In the end, they both received joint credit.

Neptune itself has the fastest wind speeds in the solar system, reaching over 1000 km/h. These wind patterns cause massive storms, and in particular the Great Dark Spot (analogous to Jupiter’s Great Red Spot). Neptune’s largest moon, Triton, is the only large moon in the solar system that orbits in the opposite direction (compared to the other moons).

Pluto

Pluto, whose planetary status is in question

Pluto, whose planetary status is in question

I know what you’re thinking. Pluto is a planet. I mean it’s so cute and rocky and we were taught from a very young age that it is the furthest planet in the solar system. But what you have to realize is that since its discovery, telescopes have gotten much more powerful and astronomers much more clever. And what they have found is that there are 50-100 objects orbiting the sun that are exactly like Pluto.

Some of these, like Eris, are bigger that Pluto. There are objects that are more like planets than Pluto is, and if we were to include Pluto as a planet then we would have to include the 50 other insignificant hunks of rock floating around our sun. There is literally nothing separating Pluto from the 50 other ‘planets’ that we have discovered. And that would be assigning equal weight to their importance.

Because as harsh as it is, there is not much that is interesting about these dwarf planets. They are just lumps of rock and ice that are indistinguishable from their moons of rock and ice.

Yes, there is a current debate. And like the naming of Uranus, some things should be up to debate. But others, like what the definition of an atom or a planet is, is not up to public vote. Because if it was, science would not function. The only reason to keep Pluto as a planet is the sentimentality of two generations of people.

That being said, Mercury is pretty much Pluto but closer to the sun. This is why definitions are so tricky, because sooner or later you will hit something that is exactly on the line that you drew in the sand. Some of those lines are easy to draw, like the line between planets and stars. Jupiter is not a star because there is no hydrogen fusion going on. If there were, it would start a chain reaction and burn brightly in the sky. But the term planet is vague. Is a pebble on the beach a planet? It’s the same thing as Pluto and Mercury, just smaller. Put a pebble and a large rock close to each other in space, and the pebble will start orbiting the rock. Make the rock bigger and bigger, and at some arbitrary point you call it a planet. Yes there are official designations, like ‘a planet’s own gravity must make it spheroidal’ but many of the planets are not perfect spheres. At which point is it spheroidal enough?

The thing we have to recognize is that definitions like these become meaningless when you actually know what is going on. Who cares about what we name the planets, or what we name as a planet? Johann Bode proved that it really doesn’t matter. Nobody today is freaking out because Uranus is the only planet named after a Greek god/a body part. What’s far more interesting is that massive worlds with conditions that we can’t even simulate here on Earth exist, within reach.

Instead of wasting time debating about semantics, let’s actually go to Titan and set up a gigantic space station there. Let’s create shuttles to Saturn to allow the people of our world to appreciate the magnificent rings and auroras. Let’s get our raw materials and energy from these lifeless worlds, rather than destroying our fragile one.

 

 

Sources:

Image of Mercury retrieved from http://www.spacestationinfo.com/Mercury.jpg

Image of Venus retrieved from http://cronodon.com/images/Venus_clouds.jpg

Image of Earth retrieved from http://teacher.scholastic.com/commclub/earth_day_activity1/assets/images/photo_cvr_earth1_hr.jpg

Image of Mars retrieved from http://haughtonmarsproject.com/wp-content/uploads/2013/11/Mars-1-Project.jpg

Image of Jupiter retrieved from http://www.picpicx.com/wp-content/uploads/2014/09/89c5c30498c2989611f9044be006197c.jpg

Image of Galilean satellites retrieved from http://static.thetimenow.com/img/astronomy/all/solarsystemwiki-Inner-structure-of-Io-Europa-Ganymede-and-Callisto.jpg

Image of Saturn retrieved from http://www.picpicx.com/wp-content/uploads/2014/09/a477f36e3056aa0f18da32cef1de7c09.jpg

Image of Saturn’s rings retrieved from http://whillyard.com/science-pages/our-solar-system/upload-images/saturn-rings-cassini-2.jpg

Image of Saturn’s auroras retrieved from http://svs.gsfc.nasa.gov/vis/a010000/a011300/a011366/cover-1024.jpg

Image of Titan retrieved from http://www.astrobio.net/wp-content/uploads/2014/06/Titan.jpg

Image of Uranus retrieved from http://msnlv.com/Uranus-planet.jpg

Image of Neptune retrieved from https://solarsystem.nasa.gov/multimedia/gallery/Neptune_Full.jpg

Image of Pluto retrieved from http://www.ennev.com/wp-content/uploads/2014/05/Pluto_impression.png

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