20 cool facts to know about Pluto



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Unanimously Pluto

In 1930, after receiving more than 1,000 name suggestions for the newly discovered planet that included Jean, Lowellofa and Zyxmal, members of the Lowell Observatory voted unanimously in favour of Pluto, the Roman god of the underworld. First proposed by 11-year-old Venetia Burney Phair (earning her a five-pound note as reward), the name won out in part because the first two letters form the initials of Percival Lowell, who led the search for the suspected ninth planet. Coincidentally, Phair’s great-uncle also named Mars’ moons Phobos and Deimos.



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Long-awaited visit

Ninety years ago, astronomer Clyde Tombaugh spotted a point of light on a photographic plate and Pluto’s existence was confirmed. In 2015, after a trek of more than six billion kilometres (four billion miles), the New Horizons spacecraft—with an ounce of Tombaugh’s ashes on board—made rendezvous with his greatest discovery.



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Plutoed

Long considered one of the nine planets of the solar system, Pluto was officially demoted to dwarf planet in 2006 after failing to meet the new definition for a major planet. The controversial decision gave rise to the term “plutoed” (meaning demoted or devalued), which the American Dialect Society declared word of the year. The decision did not sit well with many; in protest, Illinois and New Mexico passed resolutions enshrining Pluto’s planetary status, and both states declared their own Pluto Planet Day.



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Goddess of discord

It was the discovery of Eris—a rocky Kuiper Belt body about the same size as Pluto—that eventually led to Pluto’s demotion from planet to dwarf planet, kicking off a storm of controversy that continues to this day. Initially nicknamed “Xena” for the warrior princess of ‘90s television fame, Eris was formally named after the Greek goddess of discord and strife, foreshadowing the years of discord that were sown.



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King of the Kuiper Belt

Pluto is the first and largest of the Kuiper Belt objects—also known as trans-Neptunian objects, or TNOs—to be discovered. The Kuiper Belt is a distant, donut-shaped collection of possibly trillions of icy bodies orbiting the sun beyond Neptune, and a source of some of the comets that fall sunward.



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Binary

Pluto and its largest moon, Charon, make up the only binary planet in the solar system. Charon is about half of Pluto’s size, with an eighth of its mass, and their close proximity—19,000 kilometres (12,000 miles)—have brought them into mutual orbit around their combined centre of gravity, throwing the remaining four moons into somewhat chaotic orbits.



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Heart, whale and brass knuckles

Pluto’s most famous marking is the giant, heart-shaped nitrogen glacier known as the Tombaugh Regio, in honour of the dwarf planet’s discoverer. Adjacent to the heart lies an ancient, dark “whale,” the Cthulhu Macula, coated in tholins—sooty, organic macromolecules that Carl Sagan (unsuccessfully) tried to dub “star-tar.” Between the heart and the tail of the whale run the Brass Knuckles, a series of dark markings along the equator.



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The long year

Not even one year has passed on Pluto since it was discovered in 1930. The dwarf planet takes 248 Earth years to complete its run around the sun, following an elongated elliptical orbit that doesn’t follow the plane of the other planets’ orbits. These eccentricities mean Pluto can at times be closer to the sun than Neptune.



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Namesakes

In addition to spawning both a verb and an adjective, Pluto has inspired many namesakes. Disney’s most famous dog was supposedly named after the once-planet. Radioactive plutonium—used in the bombs that destroyed Hiroshima and Nagasaki—also derived its name from Pluto as it followed uranium, named for Uranus, on the periodic table. Objects in the Kuiper Belt that have an orbital relationship with Neptune similar to Pluto’s are called plutinos.



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Pluto time

Despite its vast distance from the sun, Pluto is far from dark. Even though the sun on Pluto appears 900 times dimmer than on Earth, it’s still 300 times brighter than Earth’s moon; at high noon, Pluto is as well-lit as dawn or dusk on Earth. These moments of synchronized brightness have been dubbed Pluto Time, and NASA even developed a tool to let users find out when their local Pluto Time will take place.



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Blue sky, red dunes

When the New Horizons spacecraft reached Pluto in 2015, astronomers were not only surprised to find a healthy atmosphere around the icy dwarf planet, but a hazy one at that. Organic, sooty molecules called tholins permeate the thin nitrogen atmosphere, cooling it to a chilly -203 degrees Celsius (-333 F). The reddish particles scatter the light, giving the atmosphere a blue hue (much like on Earth), and precipitate out to form ruddy dunes on the surface.



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Nitrogen tail

Pluto has a very thin, ephemeral nitrogen atmosphere, but too little gravity to hold it; nitrogen leaks away in a long tail blown by the solar wind. Scientists have yet to confirm how the dwarf planet keeps replenishing its nitrogen; the prevailing theory is that active geysers or cryovolcanoes draw deep nitrogen to the surface. The nitrogen cycle also appears to cause atmospheric winds to blow against Pluto’s spin, creating some of its unusual surface features.



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Atmospheric transfer

As Pluto’s tenuous atmosphere escapes into space, some of it travels 19,000 kilometres (12,000 miles) to settle onto the surface of its largest moon, Charon. The New Horizons probe found evidence of tholins—organic macromolecules formed from methane and nitrogen wafting from Pluto—on Charon’s north pole, painting it red, and providing essential ingredients for the emergence of life.



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Subsurface ocean

Pluto’s surface features and abundant water ice provide compelling evidence of a subsurface ocean, and the recent discovery of traces of ammonia on Pluto’s surface is bolstering the case. Ammonia breaks down fairly quickly in Pluto’s harsh environment, meaning the traces are geologically “fresh.” Ammonia also lowers the freezing point of water considerably. New research suggests a layer of gases trapped under ice acts as insulation, with possible radioactivity warming the planet enough to maintain liquid water.



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Planet Nine

Nearly 15 years after Pluto was struck from the list of the solar system’s planets, astronomers say there’s a new ninth planet out on the fringes just waiting to be found. (Ironically, one of these astronomers was also instrumental in Pluto’s demotion.) The use of the term “Planet Nine” to describe the unseen planet has raised hackles among Pluto’s defenders, who believe it disrespectful to the legacy of Clyde Tombaugh who discovered Pluto; proposed alternatives include Planet X, Planet Next and Giant Planet Five.



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