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Why Doesn't Earth Have Rings?

Saturn, Jupiter, Neptune, and Uranus all have rings, so why not Earth? Turns out, it once did. 

Planetary rings are made of a combination of ice, rock, and dust particles. They can form in a number of ways: as the result of a collision that kicks up debris; when a planetary satellite gets too close and is pulled apart by the planet's gravity; or simply from debris left behind during the planet's formation.

In the case of Earth, the space debris went on to serve another purpose. As Julia Wilde of D News explains in the video above: "The Earth had a ring too once, it just coalesced into the Moon."

Not all rings become moons, thanks to the Roche limit. Named after the 19th-century astronomer who first described it, the Roche limit is "the minimum distance that a moon or other large object can be from a planet without being torn to bits," as NASA describes. That distance is 2.5 times the radius of the planet if the orbiting object and the planet have the same density. Because the Moon is outside the Earth-Moon Roche limit of 11,470 miles, it stays intact.

But it may not always. There are theories that say that the Moon will one day become space debris and potentially form a ring around Earth, thanks to the Sun's inevitable red giant phase. David Powell writes on Space.com that billions of years from now, "as the Earth and Moon near this blistering hot region, the drag caused by the Sun's extended atmosphere will cause the Moon's orbit to decay. The Moon will swing ever closer to Earth until it reaches a point 11,470 miles above our planet." So it's goodbye Moon and hello ring—at least, until chunks of rock from the short-lived ring "rain down onto Earth's surface," Powell writes. 

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26 Facts About LEGO Bricks

Since it first added plastic, interlocking bricks to its lineup, the Danish toy company LEGO (from the words Leg Godt for “play well”) has inspired builders of all ages to bring their most imaginative designs to life. Sets have ranged in size from scenes that can be assembled in a few minutes to 5000-piece behemoths depicting famous landmarks. And tinkerers aren’t limited to the sets they find in stores. One of the largest LEGO creations was a life-sized home in the UK that required 3.2 million tiny bricks to construct.

In this episode of the List Show, John Green lays out 26 playful facts about one of the world’s most beloved toy brands. To hear about the LEGO black market, the vault containing every LEGO set ever released, and more, check out the video above then subscribe to our YouTube channel to stay up-to-date with the latest flossy content.

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Of Buckeyes and Butternuts: 29 States With Weird Nicknames for Their Residents
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Tracing a word’s origin and evolution can yield fascinating historical insights—and the weird nicknames used in some states to describe their residents are no exception. In the Mental Floss video above, host John Green explains the probable etymologies of 29 monikers that describe inhabitants of certain states across the country.

Some of these nicknames, like “Hoosiers” and “Arkies” (which denote residents of Indiana and Arkansas, respectively) may have slightly offensive connotations, while others—including "Buckeyes," "Jayhawks," "Butternuts," and "Tar Heels"—evoke the military histories of Ohio, Kansas, Tennessee, and North Carolina. And a few, like “Muskrats” and “Sourdoughs,” are even inspired by early foods eaten in Delaware and Alaska. ("Goober-grabber" sounds goofier, but it at least refers to peanuts, which are a common crop in Georgia, as well as North Carolina and Arkansas.)

Learn more fascinating facts about states' nicknames for their residents by watching the video above.

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