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Pluto’s moons

Pluto has only five moons. The largest Charon. It would appear nine times larger in Pluto’s sky than the full Moon in Earth’s sky.

Charon and Pluto always face the same side towards each other and move unusually synchronously. They both revolve around one common point in space. It’s called the barycenter. Thus, if you look from one side of Pluto, Charon is always visible and does not move across the sky, but on the other side, it is never visible.

If you were standing on Pluto’s side facing Charon, the moon would be very large in the sky. By comparison, on Earth, you could cover the Moon with your thumb at arm’s length, but on Pluto, you would need almost your entire fist. Although Charon is only 19,600 km away, it would appear nine times larger in Pluto’s sky than the full Moon in Earth’s skies.

The four small satellites are covered in reasonably pure water ice. These are Styx, Nikta, Kerberos and Hydra. Compared to the sizes of Pluto and Charon – 2300 km and 1300 km, respectively – the moons are estimated to be between 60 and 200 km across. It is believed that they appeared due to the collision of Pluto and another celestial body from the Kuiper Belt, which occurred billions of years ago. The debris of that disaster formed into smaller satellites – Nix, Hydra, Styx, Kerberos, and Charon, the knocked-out part of Pluto. 

The moons Hydra and Nyx would appear like slowly moving stars in the sky, rising and setting, while Charon would remain stationary in the sky. At noon on Pluto, the Sun looks like Jupiter from Earth. Jupiter would be the brightest planet in the sky, at magnitude 2.5—slightly fainter than the stars in Ursa Major.

And if you were to look three moon diameters away from the star-like burning Sun, you would see a very faint bluish “star”—our Earth—with a magnitude of 3.7. It would be visible to the naked eye but difficult to observe due to the sun’s glare.

Banner image: Pluto’s moons to scale. The largest, Charon, is displayed along the bottom. Credit: NASA/JHUAPL
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