Pluto and Charon

Pluto and Charon – The Eternal Dance

Common Destiny of Charon and Pluto

A tale of two rocks – Impacted, torn apart but forever side by side: Pluto and Charon!

The universe is stunning, and it seems we understand it quite fast. Or maybe we feel we were fast in last few centuries and “We Know Nothing” yet.. That’s even hard to debate.
In any case, there are many universal mysteries that could not be revealed.

Beyond how universe works with its own patterns, it is fun to stop for a while and just look from a broader perspective to humanity: You see how it pleases us? The insignificant creatures trying to search the depths of their grand home with an intellectual joy and an urge of expolaration.

While the complete scene of cosmos fascinates us with its tricks from our tiny little playground‘s point of view, even its collateral consequences nearby can include enough joy to attach us.

For instance, Pluto and Charon: The story of a timeless tango.

Pluto and Charon
Pluto and Charon in true colors, as seen by New Horizons Spacecraft. Source: NASA

On this article, we’ll present you their common destiny, how they were torn apart and became two distinct rocks.

Pluto and Charon – History of Formation

Similar to other formations within the Solar System, Charon and Pluto‘s date of birth goes back 4.5 billion years from now.

Scientists believe history of Pluto and Charon is quite similar to Earth and Moon‘s. While Pluto was yet a protoplanet, Charon (or at least some part of moon Charon) was accomodating within Plutolands. After a huge collision between proto-Pluto and another big sized planet, final but primitive versions of both rocks were ready to be shaped: Seeds of Pluto System were planted!

Pluto System members
A nice family portrait. Source here

This theory also concludes that smaller Pluto moons: Hydra, Nix, Kerberos and Styx were the survivors of that collision.

After that major incident; basic shape, formation and orbit of both celestial objects started to evolve and regulate.

Pluto and Charon – Orbit and Rotation

Charon, Pluto and other moons orbit our Sun together. While an orbit around Sun takes about 248 years, a complete Pluto-Charon tour around each other takes 6.39 days. Actually this is both a Pluto day and a Charon day at the same time. You’ll see the point.

We have mentioned about cosmic forces trying to sepearate Pluto and Charon, right.
Could this segregation cause Pluto and Charon to break up? No, it couldn’t! Luckily this colossal event did not force our lovers to a long distance relationship. Actually more pleasant days were on the way: They were not unified anymore, but the days of ogling each other were to come!

It’s quite hard to estimate the initial conditions after the grand collision. But in any case we know that after a point of stabilization, Pluto and Charon firstly became tidally locked; than switched to mutual tidal locking phase in millions of years. And for their mutual connection, they should be thankful to the resulting proximity and massive similarity following the collision!

Pluto and Charon orbit
Pluto and Charon orbiting barycenter of system. Source: Wikimedia, Credit: Tomruen

Together with the tidal locking, there is another fact about Pluto Charon System to mention: Gravitational center (barycenter) of the system is slightly shifted out from center of Pluto because of Charon’s big gravitational influence. Hence Pluto does orbit that center like other moons.

The average distances between major “centers” of Pluto System are as follows:

  • Pluto-Barycenter: 2.040km (less than a thousand kilometers from its surface)
  • Charon-Barycenter: 17.536km
  • Pluto-Charon: 19.576km

Actually Earth-Moon System’s barycenter is not the gravitational center of Earth as well, but it still lays within the properties of the Earth.

Let’s briefly explain what tidal and mutual tidal locking means with real examples:

Moon is Tidally Locked to Earth

This means that one complete orbit of Moon around Earth is (almost) equal to one complete rotation around its own axis. Hence we can only see same hemisphere of the Moon from Earth. This is common when mass of one of the objects is significantly bigger than the other and if the distance in between is short enough.

An illustration of Earth and Moon’s rotation.

Although this is not a well-known Pluto fact, tidal locking is quite common in Solar System: All planets having moons own minimum one piece possessed moon. And that leaves only Mercury and Venus out.

Speaking of possession and Mercury: Mercury is possesed by the Sun in a different manner (called spin-orbit resonance), but that’s not a point of interest for this article..

Pluto and Charon Are Tidally Locked to Each Other

In this case, both Pluto and Charon salutes each other from the same hemispheres all the time.

This video is simple and not appropriate by means of barycenter, but explains it well: The people in blue dresses on Pluto (yellow sphere) and Charon (brown sphere) can always see each other while others can never do that. Source: NASA

This can only happen when two objects are close enough in terms of mass and distance.

What makes this phenomenon more interesting is, this is a unique condition in Solar System. There are no other examples of mutual tidal locking in planetary sizes.

We Have Good and Bad News for the Earthling

Bad news is, mutual tidal locking will happen between Earth and Moon too. Because they are slowly coming towards each other. And one day, our Moon will possess our home back.

Good news: It will take so much time that you will never see it – about 50 billion years.
Well, you can actually be more optimistic as no human being can see it.

Wait, does it have to be a good news for being optimistic? Yeah, whatever! Within few billion years, there will be no Moon, Earth or Sun to talk about. Because that will be after the death of the Sun. Hence we can all relax! 🙂

Pluto and Charon – Size Comparison

Let’s chop some celestial objects!

No, we do not promote cutters. We use once and destroy them for good.

Pluto’s surface area is mostly compared with Russia‘s and it’s stated that Russia is bigger. However New Horizons Mission proved otherwise: Surface area of Pluto is slightly bigger than Russia.

What we do in common for such comparisons is to slice celestial objects from half and compare the surface area of flat side of the hemispheres.
So when you do that:

  • Pluto is smaller than Australia and bigger than India.
  • Charon is smaller than Alaska and bigger than Texas.

In terms of volume, Pluto is 170 times smaller than Earth and 3 times smaller than Moon where Charon is 6.5 times smaller than Pluto. Diameters of Pluto and Charon are 2.376,6 and 1.212kms respectively.

In terms of mass, Earth is 456 times bigger than Pluto and 3.850 times bigger than Charon.

Earth, Pluto, Charon
This certainly makes more sense than the numbers! Source: NASA

Comparing gravitational forces: Pluto has 1/16 and Charon has 1/35 of the gravitational force on Earth.

Pluto and Charon – Characteristics

Once you read about the common destiny of our lovers, you might think they have similar features. Be ready for surprises!

Weather and Temperature – Colder Than You Might Expect!

Let’s begin with similarities and save the surprises for a moment: Both Charon and Pluto are “little bit” chilly for us. While average surface temperature on Pluto is -229 ºC, Charon is slightly warmer with -220ºC.

When it comes to weather, not much to talk about Charon as she does not have a significant atmosphere. However, Pluto is an active, living planet (Yeah, Pluto is a planet). And there are some weather events on there: like methane snows and winds.

Signs of methane snow
Signs of methane snow on Pluto surface. Source: NASA

In addition to above, Pluto is eventually exposed to more temperature variations than Charon. And the reason for that is the atmosphere again! It seems the hydrocarbon particles in the atmosphere block the energy from the Sun and send it away from the planet, which keeps the planet colder than expected.

Atmospheric Comparison

As mentioned above, Pluto has an atmosphere where Charon doesn’t have a significant one. However the lover is always on duty: Researchers believe that she compromises and reduces the effects of solar winds on Pluto’s atmospheric layer.

Pluto atmosphere
Beautiful blue hazes covering Pluto atmosphere. Source: NASA

When it comes to Pluto’s atmosphere, there are words to say: We are talking about a dynamic atmosphere. It is a 160km-wide formation with several haze layers covering, where the atmospheric pressure is almost 0.00001 times of Earth’s. It mostly consists of nitrogen, methane and carbon monoxide.

Color and Albedo

Lets begin with Charon: It mostly looks like a boring piece of rock where dark grey is the dominant surface color. Does not seem to shine bright like Pluto..

And it’s not only about the color palette variations: Pluto has a bigger albedo than Charon and shining slightly better.

While red seems to be the basic surface color on Pluto surface, the true colors are mostly the shades of reddish brown.

Color calibrated views. Source: NASA

On Pluto there are wide areas with white color which mostly implies areas with higher albedo, consisting of dunes and icy materials. On the other hand, only color variation on Charon is on its north pole, and it is most probably dyed brown by the ancient love.

Surface Composition

How can a planet dye its moon? Scientists believe that color on Pluto and Charon indicates existence of tholins; organic molecules formed by engagement of methane and sunlight. Although methane is not a common material on Charon, it turns out that Pluto dispatches some of its methane and Charon welcomes them from her north pole. And that initiates the whole process.

In terms of surface materials; Pluto surface is mostly formed by nitrogen together with minor amounts of methane, carbon monoxide, water ice and ethane. However Charon surface is dominated by water ice where small amount of ammonia compounds are in company.

Surface Features

This is a chapter where our lovers resemble each other with crater zones, mountainous fields, scarps, pits and so on.

Pluto surface
A crater area on Pluto surface. Source: NASA

Sharing a mutual destiny, they have gone through similar surface formation processes like tectonism, sublimation, glaciation, erosion and cryovolcanism.

But how did they become so different after all and shifted to a complete different view? The difference lays on surface materials. Pluto surface is rich in terms of other materials and this provides her more dynamism to reshape its surface continuously. On the other hand, water ice does not ensure much options to Charon in the same manner.

If those elements on Pluto were also sweeped away in the past, Pluto and Charon would mostly look like each other.

In consequence, another question arises: How can Pluto still have those materials while Charon doesn’t? Scientists believe that’s a direct result of their love.

Charon craters
Close-up view of a crater area on Charon surface. Source: NASA

They decided to live a mutual life and Charon had to allow Pluto to steal her icy blanket. How could she beat gravity?
The massive one unintentionally captured Charon’s icy blanket and left her infertile.

For details of surface features and their names, check out the articles: Pluto Map and Charon Map.

Inner Layers

Now that we know what there is till the planetary surfaces, let’s see what’s going on down there.

About 70% of Pluto consists of its rocky core where a thinner water ice layer covers that body. Similarly, 55% of Charon is its core where the rest is the water ice.

Scientists believe core materials of Pluto, Charon and rest of the Kuiper Belt Objects are combination of silicates, sulfides and oxides in general.

Inside Pluto and Charon
Inner layers of Pluto and Charon. Scientists tend to agree on top right formation for Charon. Source here

The thrilling feature is in between surface and the cores: According to recent researches, there is a strong possibility that Pluto has an ocean of water beyond its surface; which is covered with a thin insulation layer. Charon on the other hand seems to have had a similar underground ocean before, which is estimated to be frozen millions of years ago.

Life on Charon and Pluto

When extraterrestrial life is on the table, water is always there too. Although humanity found direct evidence of water on our Moon in 1971, we were not quite sure if there were more candidates. However scientists soon realized that water is a quite common material on any kind of planetary object.

On the other hand, we were not sure that there was more water in outer Solar System regions. Existence of water on Pluto and Charon was a very important finding because researchers now believe thousands of Kuiper Belt Objects (KBO) are similar in formation. That means there are thousands of water worlds out there!

Pluto and Charon
Pluto and Charon in false colors, as seen by New Horizons Spacecraft on 14 July 2015. Source: NASA

Despite above, most of the water on KBO’s should be in ice form and this is not good for life.

Even if Pluto has an underground ocean and Charon once had before, unfortunately noone can guarantee that an ocean of water creates its life habitat. But if that is the case, there is still a possibility that at least a life in primitive way can grow.

However, such primitive organisms may not be evolved in the way we think. Because as far as we know, some of the essentials for earth-like life do not exist on Pluto or Charon.

Above all, this matter will remain as a speculation until we detect direct evidences. Plutonians and Charonians will live in our dreams for now!

Pluto and Charon in Astrology

Guess what! Similar to other celestial objects like moons, planets, stars and anything else; Pluto and Charon are not interested in your mood. They keep on dancing and it has nothing to do with you. Not everything is related with you!

And you know why:

Astrology means fairy tales.

Astronomy relies on facts. On a thing we named in last few centuries: The Science.


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