7 Surprising Facts About Pluto

NASA/JHUAPL/SwRI
NASA/JHUAPL/SwRI

Pluto, the ninth planet of the classical solar system was, until 2015, largely a mystery—a few pixels 3.6 billion miles from the Sun. When NASA's New Horizons spacecraft arrived at the diminutive object in the far-off Kuiper Belt, planetary scientists discovered a geologist's Disneyland—a mind-blowing world of steep mountains, smooth young surfaces, ice dunes, and a stunning blue atmosphere. To learn more, Mental Floss spoke to Kirby Runyon, a planetary geomorphologist at the Johns Hopkins University Applied Physics Laboratory and a scientist on the NASA New Horizons geology team. Here is what you need to know about Pluto, the small world with the biggest heart in the solar system.

1. 248 EARTH YEARS = 1 PLUTO YEAR

At 1473 miles in diameter—about half the width of the United States—Pluto is the smallest of the nine classical planets and the largest discovered "trans-Neptunian object" (i.e., an object beyond the planet Neptune). As could be expected, it is cold on Pluto's surface: around -375°F. Its gravity is about 1/15 that of Earth. It has five moons: Charon, Nix, Hydra, Kerberos, and Styx. Charon is the largest of the moons by far, with a diameter about half that of Pluto. It takes about 248 Earth years for Pluto to circle the Sun, and during that time, its highly elliptical orbit takes it as far as 49 astronomical units from our star, and as close as 30.

2. THE DISNEY DOG IS CONNECTED TO THE PLANET.

Pluto the planet was discovered on February 18, 1930 by astronomer Clyde Tombaugh at the Lowell Observatory in Flagstaff, Arizona. It was named later that year by Venetia Burney, an 11-year-old girl in England. She first learned of the new, nameless planet from her grandfather, who mentioned it while reading the newspaper. Burney was interested in Greek and Roman mythology at the time, and she immediately suggested Pluto.

Her grandfather was impressed, and mentioned it in a note to a friend of his, who taught astronomy at Oxford. The astronomy professor passed word to Lowell Observatory, and the astronomers there took an immediate liking to it. It helped that the first two letters of Pluto are the initials of the observatory's (then dead) founder, Percival Lowell. Note that Burney did not get the name from the Disney dog. Just the opposite: The dog, which premiered the same year as Pluto was discovered, was likely named by Walt to ride the planet's publicity wave. Scientists and cartoonists alike have yet to explain how the then-unseen planet and dog ended up being more or less the same color.

3. A PLUTO SYSTEM SPACE ELEVATOR IS TECHNICALLY POSSIBLE.

Space elevators are a science fiction staple, and advances in carbon nanotubes have made their prospects, if not likely, then certainly possible. The idea is to bring a large object such as an asteroid into a geostationary orbit at Earth's equator, and essentially connect that object and the Earth with a cable or structure. You could then lift things into orbit without the need for rockets. According to Runyon, the unique orbital characteristics of Pluto and Charon create interesting opportunities for the very, very distant future of engineering.

The two worlds are tidally locked. Charon's orbit is precisely the same duration as Pluto's rotation, meaning that if you stood on Pluto's surface, the moon would hover over the same spot, never rising or setting. "Because they are binary, tidally locked, literally orbiting each other in a perfect circle, you could build a space elevator that goes from one planet to the other, from Pluto to Charon," Runyon tells Mental Floss. "And it would touch the ground in both places, physically linking them. And you could literally climb a ladder from one to the other."

4. ITS HEART IS IN THE RIGHT PLACE—THE 40 PERCENT OF THE PLANET WE'VE SEEN.

In 2015, the New Horizons spacecraft arrived at the Pluto system and turned a few pixels into a real world. The famous first image released by NASA is not a straight-on shot from Pluto's side, with the top being the North Pole and bottom being the south. It is in reality a view from Pluto's higher latitudes, looking down. (The heart, in other words, is quite higher up on the planet than the picture suggests.) Because New Horizons was a flyby craft and not an orbiter, planetary scientists don't know what 40 percent of the planet looks like.

5. ITS BIZARRE ORBIT AND ROTATION ARE A MYSTERY.

The traditional classroom solar system model of a light bulb as the Sun and planets on wires extending from it represents a nice flat orbital plane known as the ecliptic, and for most of the solar system, that's pretty close to the truth. But not for Pluto, which has a 17-degree inclination relative to the ecliptic. Moreover, like Uranus, its rotation is tipped on its side, and it rotates backward (east to west). No one knows why, according to Runyon. "It's probably the result of an ancient impact," he says. "One not strong enough to disrupt planet but enough to tip on its side. This might have been the Charon-forming impact, which would be similar to how our moon is formed."

6. WE WERE WRONG ABOUT ITS ATMOSPHERE …

Astronomers have long known that Pluto has an atmosphere. During stellar occultations (that is, when it moves in front of stars), astronomers can see the star dim, and then completely go out, and then reappear dimly, and then return to its full brightness. That dimming is caused by the planet's atmosphere. Astronomers are furthermore able to track its density over time. Because Pluto is so far from the Sun, the ice on its surface sublimates: It goes from a solid directly to a gas without first becoming a liquid. When Pluto reached perihelion (as close to the Sun as its gets in an orbit) in 1989, the expectation was that the atmosphere would begin to collapse entirely: that it would freeze out, basically, and fall to the surface.

"A good comparison is when it snows on Earth," says Runyon. "Snow is basically the water vapor in the atmosphere freezing out and falling to the surface, leaving Earth's atmospheric density slightly lower than it would be otherwise." In Pluto's case, the thought was that the complete atmosphere would freeze out and fall onto the planet's surface.

It didn't happen. "Pluto's atmosphere is denser than we thought it would be," Runyon explains. "Even now as it's moving farther from the Sun, its atmosphere is puffier than ever." One model says that while the atmosphere does thin as ices fall to the surface, it never completely freezes and falls.

7. … WHICH IS ELECTRIC BLUE.

Scientists on the New Horizons team didn't expect to see Pluto's atmosphere during the flyby. "When we spun New Horizons around after closest approach and looked back at Pluto—being basically backlit from the Sun—we could see the atmosphere," he says. "We knew we'd be able to detect it, but to see it, and to see that the sunrise and sunset on Pluto is this ethereal electric blue—nobody anticipated that." Runyon says that the New Horizons found discrete atmospheric layers that could be traced for hundreds of miles. "Pluto has what's called a stably stratified atmosphere. The coldest layer is on the bottom and it gets warmer as you go up," he says.

"In science, you test hypotheses, but before you can even do that you need to figure out what's there in the first place. To me, that's the most exciting part of science. The most exciting part of space exploration is to see something for the first time, and that's what New Horizons was. And to turn around and look back at the Sun and see a beautiful atmosphere with the gorgeous layers through it is just astonishing," he says. 

The Smithsonian Needs Your Help Transcribing Sally Ride’s Notebooks

Sally Ride in 1984.
Sally Ride in 1984.
Coffeeandcrumbs, NASA, Wikimedia Commons // Public Domain

On June 18, 1983, Sally K. Ride made history when she became the first American woman to travel into space. Now, the Smithsonian Institution is making the history of her incredible decades-long career more accessible to everyone—and they need your help to do it.

The National Air and Space Museum Archives is home to the Sally K. Ride Papers, a collection of 38,640 physical pages (over 23 cubic feet) of material spanning Ride’s professional life as an astronaut, physicist, and educator from the 1970s to 2010s. Those resources have been scanned and used to create an online finding aid—not unlike a table of contents—so researchers can easily navigate through the wealth of information.

To simplify the searching process within that online finding aid, the Smithsonian Institution is asking for volunteers to transcribe documents in the Smithsonian’s Transcription Center, a digital hub launched in 2013, where anybody can sign up to type and review historical sources. Three projects from the Sally K. Ride Papers are currently available to transcribe, which include her notes for shuttle training between 1979 and 1981, notes about the Remote Manipulator System Arm (there's one on the International Space Station today), and notes from NASA commissions on which she served. One, for example, was the Rogers Commission, which investigated the causes of the fatal Space Shuttle Challenger disaster in 1986.

You can find out more about the documents in the projects here, and if you’re interested in joining the forces of “volunpeers,” as the Smithsonian likes to call its transcribers, you can create a new user account here. (All you’ll need is a username and email address.)

Check out more citizen science projects you can participate in at home here.

How to Livestream Tonight’s Super Pink Moon

Matt Cardy/Stringer/Getty Images
Matt Cardy/Stringer/Getty Images

On April 7, 2020, a super pink moon will appear over the horizon. Though it's not actually pink (the name's meaning comes from the wildflower Phlox subulata, or moss pink), the supermoon is still worth seeing. Today, the moon will reach the closest point to Earth in its orbit just hours before becoming completely full, which adds up to give us the biggest and brightest supermoon of the year. And no matter where you are in the world, you can livestream the spectacle online.

Slooh, a celestial event streaming service, will begin broadcasting the super pink moon at 7:30 p.m. ET tonight, April 7. A team of astronomy experts and educators will be joining the feed to provide commentary until the stream ends. You can tune in through Slooh's Facebook live event or YouTube channel for free, or you can become a member to watch it on their website.

Slooh has telescopes around the world that allow users to explore space from their computers. If you sign up for a membership today, you'll be able to capture and share photos of the supermoon, virtually interact with the experts at the live event, and personally control Slooh’s telescopes to customize your view of the moon. And when tonight's event is over, you'll still be able to virtually control Slooh's six telescopes in the Canary Islands and four telescopes in Chile throughout the year.

A basic, annual membership with Slooh costs $100. If you're a student, the service is offering a limited-edition price of $20 for individuals. The deal aims to promote remote teaching and learning during a time when schools around the world are closed.

For people living in cities with light pollution, celestial livestreams are a great alternative to real-life stargazing. Slooh isn't the only platform airing tonight's event. Today, the Virtual Telescope Project in Italy will host its own livestream of the super pink moon on YouTube.

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