How long is a Plutonic year

Creative saplings

Pluto was discovered by Clyde Tombaugh in 1930 and was once considered the ninth and outermost planet in the solar system. Due to the formal definition, which was adopted in 2006 at the 26th General Assembly of the International Astronomical Union (IAU), Pluto is no longer the ninth planet of the solar system and is alternately known as "dwarf planet", "Plutiod". Trans-Neptunian Object (TNO) and Kuiper Belt Object (KBO).

Despite this change in name, Pluto remains one of the most fascinating celestial bodies known to astronomers. In addition to having a very distant orbit around the sun (and thus a very long orbital period), it also has the most eccentric orbit of any planet or sub-planet in the solar system. This makes for a fairly long year on Pluto, equivalent to 248 Earth years!

Orbital time:

At the next point, Pluto actually crosses Neptune's orbit and approaches the sun. This orbital pattern occurs every 500 years. Then the two objects return to their starting position and the cycle repeats itself. They also place their orbits in a 2: 3 resonance with medium motion, which means that for every two orbits Pluto makes around the sun, Neptune makes three.

The 2: 3 resonance between the two bodies is highly stable and has been preserved over millions of years. The last time this cycle occurred between 1979 and 1999, when Neptune was further from the Sun than Pluto. In this cycle, Pluto reached perihelion on September 5, 1989 - that is, its point closest to the sun. Since 1999, Pluto has returned to a position beyond Neptune, where it will remain for the next 228 years - that is, until the year 2227.

Star and sunny day:

Similar to the other bodies in our solar system, Pluto also rotates on its axis. The time it takes to complete a single rotation around its axis is called the "star day" while the time it takes for the sun to reach the same point in the sky is called the "solar day". Because of Pluto's very long orbital period, a starry day and a solar day are roughly the same on Pluto - 6.4 Earth days (or 6 days, 9 hours and 36 minutes).

It's also worth noting that Pluto and Charon (its largest moon) are more like a binary system than a planet-moon system. This means that the two worlds orbit each other and Charon is locked in tides around Pluto. In other words, it takes Charon 6 days and 9 hours to orbit Pluto - the same amount of time it takes a day on Pluto. This also means that when viewed from Pluto, Charon is always in the same place in the sky.

In short, a single day on Pluto is approximately six and a half Earth days. A year on Pluto is 248 Earth years or 90,560 Earth days! And for the whole year the moon hangs over us and looms large in the sky. However, if you factor in the axial tilt of Pluto, you will see how strange an average year on Pluto is.

Seasonal change:

It has been estimated that to someone standing on the surface of Pluto, the sun would appear about 1000 times darker than it is on Earth. While the sun would still be the brightest object in the sky, it would look more like a very bright star than a large yellow disk. Although Pluto's eccentric orbit is very far from the Sun at any given point in time, it still results in significant seasonal fluctuations.

Overall, Pluto's surface temperature doesn't change much. Surface temperatures are estimated at a low of 33 K (-240 ° C; -400 ° F) to a high of 55 K (-218 ° C; -360 ° F) - averaging 44 K (-229) ° C; -380 ° F). However, the amount of sunlight that each side receives over the course of a year varies widely.

Compared to most planets and their moons, the Pluto-Charon system is oriented perpendicular to its orbit. Similar to Uranus, Pluto's very high axial tilt (122 degrees) essentially means that it is orbiting on its side relative to its orbital plane. This means that at a solstice, one-fourth of the surface of Pluto will experience continuous daylight while the other will experience continuous darkness.

This is similar to what happens in the Arctic Circle, where the summer solstice is characterized by constant sunlight (ie, the "midnight sun") and the winter solstice by eternal night ("arctic darkness"). But on Pluto, these phenomena affect almost the entire planet, and the seasons last for almost a century.

Even if it is no longer considered a planet (although this could still change), Pluto still has some very fascinating quarks, all of which are just as worthy of study as those of the other eight planets. And the time it takes to complete a full year on Pluto and all the seasonal changes it goes through are undoubtedly in the top ten!

We have written many interesting articles on other planets over a year here at Universe Today. Here is how long is a year on the other planets ?, Which planet has the longest day ?, How long is a year on Mercury ?, How long is a year on Venus ?, How long is a year on Earth? How long is a year on Mars? How long is a year on Jupiter? How long is a year on Saturn? How long is a year on Uranus? and how long is a year on Neptune?

For more information, visit NASA's Solar System Exploration page on Pluto and the New Horizon Mission page for information on Pluto's seasons of the year.

Astronomy Cast also features some great episodes on the topic. Here is Episode 1: Pluto's Planetary Identity Crisis and Episode 64: Pluto and the Icy Outer Solar System.