Pluto's highly elliptical orbit can take it more than 49 times as far out from the sun as Earth. Since the dwarf planet's orbit is so eccentric, or far from circular, Pluto's distance from the sun can vary considerably.
The dwarf planet actually gets closer to the sun than Neptune is for 20 years out of Pluto's Earth-years-long orbit, providing astronomers a rare chance to study this small, cold, distant world.
As a result of that orbit, after 20 years as the eighth planet in order going out from the sun , in , Pluto crossed Neptune's orbit to become the farthest planet from the sun until it was demoted to the status of dwarf planet. When Pluto is closer to the sun, its surface ices thaw and temporarily form a thin atmosphere, consisting mostly of nitrogen, with some methane. Pluto's low gravity, which is a little more than one-twentieth that of Earth's, causes this atmosphere to extend much higher in altitude than Earth's.
When traveling farther away from the sun, most of Pluto's atmosphere is thought to freeze and all but disappear. Still, in the time that it does have an atmosphere, Pluto can apparently experience strong winds. The atmosphere also has brightness variations that could be explained by gravity waves, or air flowing over mountains. While Pluto's atmosphere is too thin to allow liquids to flow today, they may have streamed along the surface in the ancient past.
New Horizons imaged a frozen lake in Tombaugh Regio that appeared to have ancient channels nearby. At some point in the ancient past, the planet could have had an atmosphere roughly 40 times thicker than on Mars.
In , scientists announced that they might have spotted clouds in Pluto's atmosphere using New Horizons data. Investigators saw seven bright features that are near the terminator the boundary between daylight and darkness , which is commonly where clouds form. The features are all low in altitude and roughly about the same size, indicating that these are separate features. The composition of these clouds, if they are indeed clouds, would likely be acetylene, ethane and hydrogen cyanide.
Pluto's rotation is retrograde compared to the solar systems' other worlds; it spins backward, from east to west. Average distance from the sun : 3,,, miles 5,,, km — Perihelion closest approach to the sun : 2,,, miles 4,,, km — Aphelion farthest distance from the sun : 4,,, miles 7,,, km — In , astronomers discovered that Pluto had a very large moon nearly half the dwarf planet's own size. This moon was dubbed Charon, after the mythological demon who ferried souls to the underworld in Greek mythology.
Because Charon and Pluto are so similar in size, their orbit is unlike that of most planets and their moons. Both Pluto and Charon orbit a point in space that lies between them, similar to the orbits of binary star systems , For this reason, scientists refer to Pluto and Charon as a double dwarf planet, double planet or binary system.
Pluto and Charon are just 12, miles 19, km apart, less than the distance by flight between London and Sydney. Charon's orbit around Pluto takes 6. This is because Charon hovers over the same spot on Pluto's surface, and the same side of Charon always faces Pluto, a phenomenon known as tidal locking. While Pluto has a reddish tint, Charon appears more grayish.
In its early days, the moon may have contained a subsurface ocean, though the satellite probably can't support one today. Compared with most of the solar system's planets and moons, the Pluto-Charon system is tipped on its side in relation to the sun.
Observations of Charon by New Horizons have revealed the presence of canyons on the moon's surface. As the textbooks were updated, the internet spawned memes with Pluto going through a range of emotions, from anger to loneliness.
But since the release of New Horizons images showing a very prominent heart-shaped feature on the surface, the sad Pluto meme has given way to a very content, loving Pluto that would like to once again be visited by a spacecraft.
The Disney cartoon character Pluto, Mickey's faithful dog, made his debut in , the same year Tombaugh discovered the dwarf planet. There is speculation that Walt Disney named the animated dog after the recently discovered planet to capitalize on its popularity, but other accounts are less certain of a direct link. But either way, the joke connecting the two, as told in the Mel Brooks film "Spaceballs " remains:. We were lost. None of us knew where we were. Then Harry starts feeling around on all the trees, and he says, "I got it!
We're on Pluto. From the bark! Pluto is a dwarf planet that lies in the Kuiper Belt, an area full of icy bodies and other dwarf planets out past Neptune. Pluto is very small, only about half the width of the United States and its biggest moon Charon is about half the size of Pluto.
Almost all the planets travel around the Sun in nearly perfect circles. But not Pluto. It takes an oval-shaped path with the Sun nowhere near its center. What's more, its path is quite tilted compared to the planets. Natural Color. Pluto is officially classified as a dwarf planet. Majestic Mountains and Frozen Plains. And compared with the other planets, the specifics of its year orbit were weird too. Still, Pluto stayed a planet. Then, in the s, astronomers started finding icy objects beyond Neptune.
Which brings us to that fateful meeting in Prague. But by the end of the week, the idea was out, and the attendees had settled on a new set of criteria for a planet: It must orbit the sun, be big enough for gravity to have smoothed it into a sphere, and be gravitationally dominant enough to clear other objects out of its orbital zone. The last rule disqualified Pluto. Read: What Pluto and California have in common.
The decision was supposed to mark the end of the Pluto discussion, not spark more debate. In the ensuing years, the arguments have settled into two camps. They argue that Pluto has a host of characteristics that qualify it for planethood: an atmosphere, geological activity, even five of its own moons. Read: The most overhyped planet in the galaxy. The experts I talked with for this story had a kaleidoscope of Pluto opinions. Some have sentimental feelings about Pluto; others are simply over it.
For many of them, the results of the New Horizons flyby in make discounting Pluto difficult.
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