7 Surprising Facts About Pluto


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.


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.


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.


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."


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.


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."


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.


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. 

LEGO Built a Life-Sized Astronaut Model to Celebrate the 50th Anniversary of Apollo 11

The LEGO Group
The LEGO Group

The LEGO Group is honoring the 50th anniversary of the Apollo 11 mission in a way that only LEGO can: with a life-sized astronaut model constructed entirely from LEGO blocks.

The 6-foot-3-inch model matches the space suit worn on the Moon by astronaut Edwin “Buzz” Aldrin on July 21, 1969, down to the American flag patch on his left shoulder. The front of the helmet even mimics the well-known photo of Aldrin standing on the Moon’s surface, with his helmet reflecting his own shadow and fellow Moon-walker Neil Armstrong in the near distance.

The feat took a team of 10 designers and LEGO Master Builders 300 hours and 30,000 LEGO bricks to complete, and you can see it in person on Washington, D.C.’s National Mall as part of the Smithsonian’s National Air and Space Museum’s Apollo 50 Festival from July 18 to July 20.

Though the astronaut model is already complete, there’s still tons to build—during the festival, you can help Master Builders assemble mosaic backdrops of the Moon and Mars, and you can even lend a hand in the construction of a 20-foot-tall replica of NASA's Space Launch System rocket, the vehicle NASA is developing to potentially use to send humans to Mars in the future.

The LEGO Group is also displaying an 11-foot-tall replica of a rocket at the Ontario Science Centre in Canada from now through September 2. It contains not only an impressive 80,000 bricks, but also built-in lights, sound, and a fog machine to simulate a rocket launch.

Buzz Aldrin on the Moon
Buzz Aldrin walks on the Moon.
NASA, Wikimedia Commons // Public Domain

It’s all part of a LEGO initiative to inspire a new generation of children to be enthusiastic about—and personally involved in—the future of space exploration. In addition to its brick-based efforts, the company is currently partnering with Scholastic on a program to send 50 kids to NASA Space Camp next year. “We will continue to inspire children to dream about what’s possible and to grow up to pursue STEM careers, said Bettina Inclán, associate administrator for communications at NASA’s Washington, D.C. headquarters.

Check out LEGO’s space-related collections—featuring Mars exploration, women of NASA, a recreation of the Moon landing, and more—on its online store.

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A Half-Blood Thunder Moon Will Light Up Tonight’s Sky

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

Today, July 16, 2019, marks 50 years since NASA launched the Apollo 11 lunar mission. In case you needed another reason to look up at the sky on this date, tonight's Moon will be a special one. It's the only full moon of July, and in some parts of the world, it will appear partially eclipsed, making for a rare half-blood thunder moon, according to Space.com.

The meaning of the name thunder moon has nothing to do with lightening and storm clouds. The full moon of each month of the calendar year is given a special nickname from folklore. January's is a wolf moon, March's is a worm moon, and June's is a strawberry moon. The full moon that appears in July is commonly called a thunder moon, because thunderstorms are frequent this time of year, but it can also be referred to as buck moon because July is when deer antlers are at their fullest.

There's another factor that makes tonight's Moon worth watching. Starting at 2:43 p.m. EDT, the Moon will enter a partial lunar eclipse. That means part of the full moon will pass through the shadow of the Earth, making one section of it appear darker than the rest. A full lunar eclipse is known as a blood moon due to the reddish hue it takes on in our planet's shadow. Tonight's event isn't a full eclipse, so it's being called a half-blood moon even though it may not take on a coppery tone. The partial lunar eclipse will reach its peak at 5:30 p.m. EDT, and conclude at 8:17 p.m. Unfortunately that means the eclipse won't be visible from the U.S., but spectators in Europe, Africa, South America, and parts of Asia will get to see the full show.

July is shaping up to be an exciting month for stargazers. On July 9, Saturn reached opposition, making it look especially large and bright in the night sky. The planet is no longer at peak visibility, but it will be easy to spot with the naked eye from now through September. If you're already planning at looking up at the Moon tonight, here's how to find Saturn at the same time.

[h/t Space.com]