Puzzling Pluto

Imagine a heavenly object that is about 0.0025 times the Earth’s mass, with a diameter that is lesser than even that of our moon (in fact lesser than that of six other moons in our solar system), surely you wouldn’t call such an object a planet, but that is exactly what Pluto is and with good reasons.

The God of the underworld
Pluto is the god of the underworld in Roman mythology, and since the planet is so far away from the sun & is almost always in darkness, it was named thus.

An eccentric planet
The outermost known planet of our solar system, Pluto is the ninth planet from the sun and is at an average distance of 5.9 billion km. It orbits the sun once every 248 Earth years in a highly elliptical orbit, and at a tilt of 17 degrees relative to the plane of the ecliptic, which is much more than any of the other planets. And only about one-fourth of its orbit has been observed till date as the planet was discovered only in the 20th century.
An interesting fact is that due to its eccentricity or more appropriately that of its orbit, Pluto’s orbit lies inside that of Neptune’s (the 8th planet) during certain parts of its travel around the sun (for e.g. from 1979 to 1999); thus truly speaking, it could not be termed the outermost planet, at least during such periods. But since its average distance from the sun is greater than that of Neptune, it has been denoted as the ninth planet.

It’s an asteroid, it’s a moon, it’s Pluto
Those who believe that Pluto is not a planet have good reason to do so. Its relatively smaller size plus its wayward orbit has lead to the theory that Pluto is actually an escaped moon, probably that of Neptune. In fact Pluto with its inferred density of 2 gm/cc is similar in structure to the moons of the giant planets. But although Triton (a moon of Neptune) and Pluto are very similar, it is believed that Triton was in fact an independent entity like Pluto but was captured by Neptune.
Then there are those who think that Pluto is probably an asteroid or even a comet. But the fact that Pluto has enough gravity to retain its spherical shape, has seasons as well as some semblance of an atmosphere is probably enough to classify it as a planet.

You wouldn’t want to vacation here
The huge distance between the two planets as well as its relatively smaller size makes it difficult to study the planet from Earth but the Hubble Telescope helped immensely in revealing some of the secrets that the planet holds.
Pluto’s surface temperature varies between 35 and 45 K (-378 to -396 F or -228 to -238 C). And although its composition is unknown, its density of about 2 gm/cc probably means that it is a mix of about 70 % rock and 30 % water ice. But certain parts of the planet may have organic materials that keep those parts warmer than the rest of the planet.
Also not much is known about Pluto’s atmosphere, but it is considered to be primarily made up of nitrogen plus some carbon monoxide, methane and ethane. Pluto has very large ice caps that remain frozen during most of its orbit around the sun, but when it is closest to the sun, these ice caps melt and the gases released help in forming the atmosphere. Even then the atmosphere there is very thin and Pluto’s atmospheric pressure is 100,000 times less than that on Earth. It is assumed that these gases either condense and fall onto the planet as frost or escape into space.

Moon or a double planet
Pluto's moon, Charon was discovered in 1978 and is named after the mythological figure who ferried the dead across a river and into the underworld, but it is said that the discoverer of Charon also named it after his wife Charlene.
Charon’s surface is very dark as compared to Pluto and it is assumed that it is covered with dirty ice water. And like the Earth & the moon, these two also keep the same sides towards each other. It is thought that Charon, much like our moon, was formed by an impact between Pluto and another object.
Interestingly, Charon does not actually revolve around Pluto; the two of them orbit around a common centre of mass (their barycentre). Another reason why the two are thought to be double planets is that Charon is nearly half the size of Pluto, which is very unusual in planet-moon systems (in fact until the discovery of Charon, our moon was the largest amongst all the moons when compared to their primary planets)

So until a spaceship does visit Pluto, it will remain and retain some of its enigma. After all what’s life without a little mystery?