Photo by: Shutterstock

Shutterstock

Pluto and Neptune Swap Places Every 248 Years

By: Reuben Westmaas

The farthest planet in our solar system varies.

August 01, 2019

Pluto has had a rough time of it. Sure, the Earth is full of people wearing novelty T-shirts proclaiming their loyalty to what used to be called the smallest planet, but it doesn't change the fact that scientists won't let it back in the planet club. At least it got a couple years of being the farthest planet from the sun before having its status ripped away. Except, if you were alive between 1979 and 1999, then the farthest planet in the solar system was Neptune for a few years of your life.

The Cosmic Dance

Once you get all the way out to the far reaches of the solar system, things start operating at a much slower pace. Think of it this way: Pluto was discovered in 1930 and it had its planet status revoked in 2006. In the 76 years between those two dates, it had only covered about three-tenths of its orbit around the sun. It won't be until 2178 that it will complete its first full "year" since its discovery. Who knows what we'll be counting as a planet then?

Because the orbit of Pluto is 248 Earth years, that's exactly how often we get to spot another quirk of the black sheep astral body. Every so often, Pluto's elliptical orbit brings it closer to the sun than its nearest neighbor, Neptune. It's all about the perihelions.

The perihelion is the point at which an object is closest to the sun, while the aphelion is the point that it's farthest. These two points are generally measured in AU (astronomical units). One AU is the average distance between the Earth and the sun: about 93 million miles (150 million kilometers).

For context, the Earth's perihelion is 0.98 AU and its aphelion is 1.01 AU — thanks to our mostly circular orbit, there's not a huge difference between the closest and the farthest points. But since Pluto's orbit is so elliptical, its perihelion is much, much, much closer to the sun than its aphelion. At the farthest point, it's 49.5 AU away (in other words, almost 50 times farther from the sun than the Earth is), but it swings up to 29.7 AU at its closest. By contrast, Neptune's orbit is almost as circular as Earth's, ranging from 30.4 AU to 29.8 AU. That means that every single time Pluto makes an orbit, its closest point comes in 0.1 AU (9.3 million miles, or 15 million kilometers) closer than the ice giant next door.

Wacky Ways

The fact that Pluto's orbit is so stretched out and elliptical isn't the only strange thing about it. It's also inclined at an angle of 17 degrees. While all of the eight planets (it's still painful to write that) lie in a relatively flat plane in relation to the sun, Pluto's orbit is at a sharp angle to the rest, like a seesaw stuck in one position. Although its strange orbit didn't play a role in disqualifying Pluto for planethood, it probably comes down to the same factor: size. Scientists aren't positive, but the leading explanation for Pluto's weird behavior is that it's just so small that Neptune has a significant effect on its motion. Over the past 4.5 billion years, the smaller body has been buffeted and slingshotted by the gravity of the larger planet, and the result is an orbit that's unlike any planet's (but not unlike that of other objects in the Kuiper Belt). We'll say this: Pluto may have lost its planet status, but with all of its weirdness, it will never lose its place in our hearts.

This article first appeared on Curiosity.com.

Next Up

The Secret of Pluto’s Ocean

When we think of an ocean, we don't necessarily think of Pluto. If we can’t see the liquid water, why do astronomers think it’s there?

Why Does Pluto Have Such a Weird Orbit?

Pluto is the black sheep of the planets in our solar system and it looks like astronomers aren’t sure how long Pluto will remain in its present orbit.

For the Love of Pluto

As we celebrate the 90th anniversary of Pluto’s discovery, we are forced to examine and reflect on the planetary status of the formerly recognized 9th planet in our solar system. #TeamPluto premieres Tuesday, February 18th at 11pm ET/PT on Discovery and Discovery GO.

Get Celestial with Lowell Observatory LIVE!

Our friends at Lowell Observatory are serving up our solar system on a platter live!

Celebrating Hubble's 30 Year Legacy

Three cheers for the Hubble! First launched in 1990 aboard the Space Shuttle Discovery, the storied space telescope is celebrating is thirtieth year in lonely orbit around the Earth.

May Sky Watch: What to Look Out For This Month

Whether you can see it from home or stream it online, here are some of May's wonderous celestial events.

How Did the Solar System Form?

How did our solar system form? It's a pretty simple and straightforward question, but as with most things in science, simple and straightforward doesn't necessarily mean easy.

Following Blue Origin’s NS-12 Rocket Launch

Blue Origin, Billionaire Jeff Bezos’ spaceflight company, is rescheduled to launch its NS-12 reusable spacecraft on Wednesday, December 11. Watch it LIVE.

Lowell Observatory Astronomers Celebrate Hubble

Astronomers from Lowell Observatory in Flagstaff, Arizona celebrate the 30th Anniversary of the Hubble Space Telescope with personal stories from their research.

Check out the Earth’s 800,000 Year Old Battle Wound

Scientists may have discovered the location of an ancient buried crater, a result of a meteorite that barreled into the Earth some 800,000 years ago.