Upon reception of new data and photographs from the New Horizons mission that flew by Pluto on Tuesday, scientists are now reporting that, unlike the earth and the moon’s orbit, Pluto and Charon have quite a divergent orbit. It’s so different, in fact, that it is the only instance of this type of orbit in the solar system.
What’s different about Pluto and Charon’s orbits?
The data from the mission revealed new information about both Pluto and Charon. It was found that Pluto is only somewhere around 8 ½ times more massive than its moon Charon. On top of this, Pluto and Charon are only 12,200 miles (19,634 km) apart. To put this in perspective, Earth is about 81 times more massive than the moon and are 238,900 miles (384,472 km) apart. Because the differences in mass are so minute and because they are so close, Charon doesn’t actually orbit around Pluto.
In reality, Pluto and Charon have what is known as a binary system, and this is the only orbit of its kind in our solar system. What this means is that the small difference of masses and the close proximity causes both cosmic bodies to pull on each other, creating a gravitational point between the two that Pluto and Charon both orbit.
How is this orbit possible?
Scientists first reactions were that Charon was once a piece of Pluto that was broken off due to a cataclysmic collision with another planetoid. This is very similar to how our moon was formed. However, further investigation shows that Pluto and Charon are almost too different for that theory to be viable.
Pluto is very rocky and has a very thick atmosphere while Charon is made of about as much ice as it is rock and has no atmosphere at all. There are nitrogen, methane, and carbon monoxide ices on Pluto, but Charon mainly has water and ammonia ice. As of now, it is clear that the two bodies have been together for billions of years, yet they are so incredibly different.
What about Pluto’s other moons?
Pluto has four other, smaller moons besides Charon: Hydra, Nix, Kerberos, and Styx. Like Pluto and Charon, they also orbit the gravitational point the two larger bodies create. Because they orbit two different cosmic bodies, the sun could rise in the east and set in the west on one day, then rise in the west and set in the south on another. Since the four smaller moons orbit the gravitational pull at a farther distance, it is safe to say that the binary system of both Pluto and Charon have four moons.
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