50 Fun Facts About Pluto

Who discovered Pluto in 1930?

He was a 24-year-old self-taught farm boy from Kansas hired by Lowell Observatory to hunt for Planet X.

What device did Tombaugh use to spot Pluto moving between two photographic plates?

Flicking rapidly between plates makes anything that has moved appear to jump.

Where was Pluto discovered?

Percival Lowell had founded it in 1894 and started the search for a ninth planet in 1906.

Who first suggested the name Pluto?

Venetia Burney of Oxford proposed it to her grandfather over breakfast; he passed it to an astronomer who cabled Lowell.

The name Pluto had an extra attraction: its first two letters were the initials of whom?

The planetary symbol became a PL monogram, still used in astrology.

Pluto is named after the Roman god of what?

The name is also an epithet of Hades, his Greek equivalent.

What was the Lowell staff's first-choice name for Pluto, rejected because an asteroid already had it?

Minerva, Pluto and Cronus topped the list of over a thousand suggestions.

Which element was named after Pluto in 1941?

Glenn Seaborg followed the tradition of uranium and neptunium.

Which cartoon character was apparently named after the newly discovered Pluto in 1930?

Disney animator Ben Sharpsteen could never confirm exactly why the pup got the name.

In what year did the IAU redefine 'planet' and reclassify Pluto as a dwarf planet?

Many planetary scientists still refuse to accept the demotion.

Which of the IAU's three planet criteria does Pluto fail?

Its mass is only 0.07 times that of everything else in its orbit; Earth's is 1.7 million times.

The discovery of which more massive object in 2005 forced the debate over Pluto's status?

The press called it the tenth planet; the IAU instead made both it and Pluto dwarf planets.

What minor-planet number was Pluto given in 2006?

Brian Marsden had suggested number 10000 in 1998; that idea was howled down.

Pluto is a member of which region of the Solar System?

It was the first Kuiper belt object found, six decades before the second.

How long does Pluto take to orbit the Sun?

It has not completed a single orbit since its discovery, and will not until 2178.

Between 1979 and 1999, where was Pluto relative to the eighth planet?

Its eccentric orbit dips inside Neptune's for about 20 years of each circuit.

Why can Pluto never collide with Neptune despite crossing inside its orbit?

Pluto completes two orbits for every three of Neptune's, and objects sharing this rhythm are called plutinos.

Pluto's orbit is tilted to the plane of the planets by more than how much?

Combined with its eccentricity, that sets it apart from the eight planets' near-circular, flat orbits.

How long does sunlight take to reach Pluto at its average distance?

That is at 39.5 AU, roughly 5.9 billion km.

How does Pluto's mass compare with the Moon's?

Its volume is about a third of the Moon's; it is less massive than seven moons in the Solar System.

What is Pluto's diameter?

That is a little bigger than Eris, though Eris is heavier.

Pluto's surface area is roughly the size of which country?

About 17.7 million square kilometres, slightly larger than Russia.

How many known moons does Pluto have?

Charon plus the tiny Styx, Nix, Kerberos and Hydra.

Pluto's largest moon is so big that the pair are sometimes called what?

Their centre of mass lies outside Pluto, and each keeps the same face to the other.

Who discovered Pluto's largest moon in 1978?

He named it after his wife Charlene's nickname 'Char', dressed up to sound like the underworld ferryman.

Charon's discoverer named the moon partly after whom?

Which is why he pronounced it with a 'sh' sound, unlike the mythological ferryman.

What did the discovery of the largest moon finally allow astronomers to measure?

It came out at just 0.2% of Earth's, far too small to be Lowell's Planet X.

Which spacecraft flew past Pluto on 14 July 2015?

It had left Earth in 2006, when Pluto was still officially a planet.

What unusual cargo, honouring the 1930 discovery, rides aboard the Pluto flyby spacecraft?

About 30 grams of Clyde Tombaugh's ashes are on board.

Which planet gave the Pluto probe a gravity assist in 2007?

The boost shaved years off the 3,462-day trip.

What is the informal name of the large bright heart-shaped region the flyby revealed on Pluto?

Its western lobe is Sputnik Planitia, a vast basin of frozen nitrogen.

Sputnik Planitia, the western lobe of Pluto's 'heart', is what kind of feature?

Its polygonal cells are convection cells in the nitrogen ice, and it shows no craters at all.

Pluto's plains are made of more than 98% what?

The mountains, by contrast, are made of water ice, which is rock-hard at Pluto's temperatures.

Pluto's thin atmosphere consists mainly of which gases?

They are in equilibrium with the ices on its surface, and the pressure dropped 20% between 2016 and 2019.

How long is a day on Pluto?

Like Uranus it spins on its side, with an axial tilt of about 120 degrees.

What is Pluto's axial tilt?

At solstice a quarter of the surface is in permanent day and another quarter in permanent night.

Pluto is roughly how many times more massive than Ceres, the largest object in the asteroid belt?

It is also more than twice Ceres's diameter, yet still lighter than Eris.

Which moon, bigger than and similar to Pluto, is thought to be captured from Pluto's region?

An early theory even had Pluto as an escaped moon of Neptune knocked loose by Triton.

Pluto's Japanese name Meiōsei, borrowed into Chinese and Korean, means what?

Houei Nojiri coined the calque, matching 'sea king star' for Neptune.

Objects that share Pluto's 3:2 orbital resonance with Neptune are called what?

The cycle of close approaches repeats every 495 years, and Neptune and Pluto never come within 17 AU of each other.

How many days did the flyby probe's journey to Pluto take?

That is about nine and a half years; the last data from the flyby arrived in October 2016.

In 1931, based on its supposed tug on Neptune and Uranus, Pluto was reckoned as massive as what?

Estimates shrank all century until Charon revealed the truth: 0.2% of Earth.

Scientists suspect Pluto may hide what beneath its icy crust?

Radioactive heating could keep a 100 to 180 km layer liquid at the core-mantle boundary.

Alan Stern has pushed for a return orbiter launching around which anniversary year?

It would use Charon's gravity to steer itself around the system.

Where was Pluto's discoverer raised, largely teaching himself astronomy and grinding his own lenses?

He was born in Illinois in 1906 and moved to Burdett, Kansas after a failed corn harvest.

The most common astrological symbol for Pluto shows an orb over what weapon of the god?

The orb may represent Pluto's cap of invisibility.

Where was the earliest known precovery image of Pluto taken, on August 20, 1909?

Percival Lowell's own surveys caught Pluto twice in 1915 without anyone recognising it.

Why did the search for 'Planet X' stall for about a decade after Percival Lowell's death?

Constance Lowell's ten-year fight over the estate meant the search did not resume until 1929.

In which year was Kerberos, the fourth of Pluto's moons to be found, discovered?

Nix and Hydra were found in 2005 and Styx, the last, in 2012.

A 2022 study proposed that Wright Mons and Piccard Mons are mergers of many smaller what?

That would imply an internal heat source at levels previously thought impossible for Pluto.