6 things to know about Pluto in advance of NASA's New Horizons mission

An artist's concept shows the New Horizons spacecraft as it approaches Pluto and its largest moon, Charon, in July 2015.
An artist's concept shows the New Horizons spacecraft as it approaches Pluto and its largest moon, Charon, in July 2015.
Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

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This Thursday, NASA's New Horizon probe will start sending back pictures of Pluto.

Those images will help scientists finally get a sense of what the dwarf planet's surface is like, said Bonnie Buratti of the Jet Propulsion Laboratory.

"We don’t know in the big picture, what it looks like," she explained.

Right now, our best images are blurry and pixilated, but New Horizons will fix that by snapping photos as it approaches a close range flyby later this summer.

"We don’t really know if it’s active," Buratti said of the dwarf planet. "Whether frosts are moving around, whether we will see lots of craters. We might see plumes or volcanoes."

Nine years ago when New Horizons launched, George W. Bush was still President, Miley Cyrus was still Hanna Montana, and Pluto was still a planet.

Later that year the International Astronomical Union demoted Pluto to a dwarf planet.

Still, as the tenth largest object directly orbiting the sun, it's worth exploring. Below are some interesting facts about our very distant neighbor.

1. Pluto has 5 moons

For such a small place, Pluto has a lot of hangers-on. The dwarf planet has no less than five known moons, named  Charon, Styx, Nix, Kerberos, and Hydra.

2. Pluto has the largest moon relative to its size in our solar system

Pluto's largest moon Charon is about 750 miles in diameter, making it just over half the size of Pluto itself. It has roughly 12 percent of the mass of Pluto as well.

"It's almost like a double planet... it's big compared to Pluto," noted Bonnie Buratti of JPL.

Charon is also tidally locked with Pluto, meaning if you were to stand on the surface of the dwarf planet, you would always see the same side of Charon as it orbits. Earth's moon is similar in that way.

3. Pluto has an egg shaped orbit around the sun

While the planets tend to have a mostly circular orbit, Pluto revolves around the sun in an elliptical fashion.

That means sometimes it is farther from the sun than the most distant planet, Neptune, and other times it is closer.

Pluto also orbits on a plane that is slightly inclined from the planets, making its trek around the sun a truly unique one.

4. Pluto has a nitrogen-based atmosphere

We still know relatively little about the surface of Pluto itself, but we do know it has a thin atmosphere around it.

It's made up of primarily nitrogen, much like the atmosphere on Earth. However, rather than oxygen, Pluto is surrounded by lots of methane with possible traces of hydrocarbons and argon, according to Buratti.

Pluto's atmosphere is also significantly weaker than ours, she noted.

"Only a few millionth's of the pressure of Earth's atmosphere."

5. Pluto is very, very cold

It's no surprise that an object that is on average 3.6 billion miles from the sun is a cold, cold place. Buratti says Pluto is one of the two coldest things with a surface known in our solar system.

The other is Triton, the largest moon of Neptune.

Pluto can reach temperatures of -400 degrees Fahrenheit, Buratti noted.

"That is colder than we can imagine."

6. Pluto was discovered by a Kansas farm boy

During the Great Depression, a young farm boy from Kansas named Clyde Tombaugh worked at the famous Lowell Observatory in Flagstaff, Arizona.

Legend has it he was offered a job after he sent pictures of planets he drew based on observations from home made telescopes.

During his time at the observatory, Tombaugh was tasked with seeking out distant objects in the solar system.

"He practically lived at the observatory," Buratti said. "And did this tedious work of looking for little moving objects... and he found Pluto."

Tombaugh died in 1997 and his ashes were added to the New Horizons probe. This July they will finally pass by the planet Tombaugh discovered back in 1930.

Caption: Clyde Tombaugh, astronomer and discoverer of Pluto

Correction: An earlier version of this story misstated how cold Pluto can get. KPCC regrets the error.