50 Fun Facts About Kuiper Belt

The Kuiper Belt lies 30 to 50 AU out, where one AU is the Sun's distance from which planet?

Earth's average distance from the Sun defines the astronomical unit; at 30 to 50 times that, the belt's bodies are so faint that it went undetected until the 1990s.

The Kuiper Belt is a far larger, more distant cousin of which band of rubble?

The asteroid belt never gathered into a planet because Jupiter's gravity kept stirring it; both bands are leftovers from the Solar System's birth that a giant planet went on to shape.

Unlike rocky asteroids, most Kuiper Belt objects are composed largely of what?

Frozen ices like methane and water stay solid in the deep cold so far from the Sun, whereas the asteroids formed close enough in that mostly rock and metal were left.

Gerard Kuiper, the astronomer the belt is named for, was born and educated in which country?

Netherlands-born Kuiper left Leiden for America in 1933 and in 1964 predicted the Moon's surface would feel like crunchy snow underfoot, as Neil Armstrong confirmed five years later.

Which Irish astronomer proposed a disc of small bodies beyond Neptune in the 1940s, lending the belt its other name?

Kenneth Edgeworth reasoned in 1943 that matter so far out was spread too thin to build planets and formed countless small bodies instead, hence the name Edgeworth-Kuiper belt.

Pluto was named in 1930 by an 11-year-old schoolgirl after the Roman god of what?

The underworld was Venetia Burney's idea: the Oxford schoolgirl suggested its god's name to her grandfather, who passed it along until the Lowell Observatory adopted it.

Kuiper's 1951 paper assumed what about Pluto, which would have meant no belt survives today?

It was a massive planet, he reasoned, whose gravity had flung the comets away; the moon found in 1978 let astronomers weigh Pluto, which has about a sixth of our Moon's mass.

Which two astronomers announced the first modern Kuiper Belt object, 1992 QB1?

David Jewitt and Jane Luu, who joined the hunt as his graduate student, searched for years, first on photographic plates and then with digital cameras, before the object finally showed up.

Which name from William Blake's mythology did 1992 QB1 finally receive in 2018?

Albion is the island-dwelling first man of the poet's myths and an old name for Britain; its finders had wanted to call it Smiley, but an asteroid already held that name.

Classical Kuiper Belt objects are nicknamed 'cubewanos' after what?

The QB1 in 1992 QB1's designation, said aloud, gives cue-bee-one-o; these 'classical' objects have the calm, near-circular orbits theorists first expected of the whole belt.

The graduate student who co-discovered the first Kuiper Belt object reached America in 1975 as a refugee from which country?

Vietnam's southern capital fell in 1975 and her family fled to relatives in Kentucky; within a decade she had won a scholarship to Stanford, and at MIT she joined the search that found the belt.

Which device, used to spot moving objects between paired photographs, did Pluto's discoverer rely on in 1930?

A blink comparator flips between two plates of the same patch of sky, so anything that moved seems to jump while the stars stay put; Pluto gave itself away that way in February 1930.

Roughly how many Kuiper Belt objects at least 100 km across are thought to exist?

Hundreds of thousands are thought to be out there, yet they are so faint and far away that only about 2,000 objects of any size had been catalogued by 2018.

Which unstable region overlapping the Kuiper Belt's outer edge is still being stirred by Neptune's gravity?

The scattered disc holds bodies Neptune flung onto wild, elongated paths that it can still disturb, so the region slowly loses them, while the main belt has stayed far more stable.

Long-period comets fall in from which vast spherical shell of icy bodies far beyond the Kuiper Belt?

The Oort cloud is too distant to be seen directly; Jan Oort inferred it in 1950 because such comets arrive from every direction instead of along the plane the planets share.

Kuiper Belt objects that share Pluto's 2:3 orbital resonance with Neptune are known as what?

Plutinos share Pluto's beat of two laps for every three of Neptune's, the rhythm that keeps Pluto from ever nearing the giant even though its path crosses inside Neptune's orbit.

William Shatner campaigned for which name, which topped a 2013 public vote for a Pluto moon before the IAU rejected it?

Vulcan won after the Star Trek actor urged fans on, but the name already belonged to a once-suspected planet inside Mercury's orbit, so the two moons became Kerberos and Styx.

The belt's outer edge, where objects suddenly all but vanish near 50 AU, has been nicknamed the Kuiper what?

Cliff fits because the drop is so steep: no theory had predicted the belt would simply stop, and one proposed culprit is an unseen planet at least the size of Mars sweeping the zone clean.

Because its bodies stray well above and below the planets' plane, the Kuiper Belt is shaped less like a belt than what?

A torus or doughnut is the better picture because Neptune's gravity kicked many members well out of the planets' plane, puffing what might have been a thin band into something far thicker.

Despite the labels, the 'hot' and 'cold' groups of classical Kuiper Belt objects are defined by what?

Orbital tilt is the dividing line: the cold group circles calmly near the planets' plane, while Neptune's gravity is thought to have pumped the hot group onto tilted, stretched paths.

New Horizons draws its electricity from the radioactive decay of which element?

Plutonium was itself named after Pluto, then counted as a planet, following uranium and neptunium up the periodic table; the probe's generator turns the heat of its decay into electricity.

Which theory of how migrating giant planets reshaped the early belt is named after the French Riviera city where it began?

The Nice model, worked out in 2005 at the Côte d'Azur Observatory, has shifts in Jupiter's and Saturn's orbits drive Uranus and Neptune outward through a dense disc of icy bodies, flinging most of it away.

Which large moon of Neptune is thought to be a captured Kuiper Belt object, the only big moon with a retrograde orbit?

Triton was spotted in 1846, only weeks after Neptune itself; a moon born beside its planet would circle the same way the planet spins, so this one is thought to have formed elsewhere and been caught.

Voyager 1 could have flown on to Pluto, but mission planners chose a close pass of which moon instead?

Titan won because its substantial atmosphere was a prime target, and the close pass threw Voyager 1 out of the planets' plane for good, so Pluto went unvisited until 2015.

Pluto was discovered in 1930 by which astronomer, making it the first known Kuiper Belt object?

Clyde Tombaugh had no formal training: he built his own telescope and mailed the observatory his sketches of Jupiter and Mars hoping for advice, and the reply was a job offer.

Pluto was demoted in 2006 for failing which test of a full planet?

Clearing its orbit is the one test Pluto fails, since it shares its zone with a swarm of other icy bodies; it does circle the Sun and is round, which is what makes it a dwarf planet.

Which moon is over half as wide as Pluto itself?

Charon was found in 1978 by James Christy, who chose the mythical ferryman's name partly because its first four letters matched his wife Charlene's.

How long does sunlight take to reach Pluto at its average distance of 39.5 AU?

About 5.5 hours at the speed of light: from that far out the Sun delivers only a sliver of Earth's daylight, yet at noon it still shines hundreds of times brighter than our full Moon.

Which distant world, found in 2005 and at first thought bigger than Pluto, forced the IAU to define what a planet is?

Eris was briefly billed as the tenth planet, but more finds like it were expected, so in 2006 the IAU wrote a definition instead, and Pluto itself fell short of it.

Eris is named after the Greek goddess of what?

Strife and discord were her trade, and the moon Dysnomia is named for her daughter, the spirit of lawlessness; until 2006 the finders simply called their find Xena, after the TV warrior.

Which Caltech astronomer, whose Palomar team found Eris and Makemake, titled his memoir How I Killed Pluto?

Mike Brown's finds made it clear that Pluto was only one of many such worlds, in the words of his 2012 Kavli Prize citation; the book's full title adds 'and Why It Had It Coming'.

Haumea is named after a goddess of childbirth and fertility from which culture?

Hawaiian myth makes Haumea the mother of Hi'iaka, patron of the Big Island and of hula dancers, and of the water spirit Namaka, which is why the dwarf planet's two moons carry their names.

In October 2017, Haumea became the first trans-Neptunian object and dwarf planet found to have what?

A ring system turned up when astronomers watched Haumea pass in front of a star; the dwarf planet spins so fast, about once every four hours, that it is stretched into the shape of an American football.

Makemake, named for a Rapa Nui god, was nicknamed after which holiday?

Easter had passed days earlier when the Palomar team spotted it in 2005, hence the nickname Easterbunny; Rapa Nui is Easter Island, whose people's creator god supplied the formal name.

When New Horizons looked back at Pluto's thin atmosphere in 2015, its hazes glowed what colour?

Blue, to the team's surprise: the haze particles are probably grey or red themselves, but they are small enough to scatter blue light, much as the molecules of air tint our own sky.

Sedna last swung close to the Sun in which era?

The end of the Ice Age was the comparison its finder drew when announcing it in 2004: one lap of Sedna's long, stretched orbit takes more than 10,000 years.

Gonggong, a distant dwarf planet named by public poll in 2019, takes its name from what?

A Chinese water god with red hair and a serpent's tail, Gonggong is blamed in myth for floods and chaos; the finders put three names to an online vote, and he beat a German winter goddess and a Norse deity.

When New Horizons reached Pluto in 2015, its pictures revealed a huge bright region in what familiar shape?

A heart, much of it a vast glacier of frozen nitrogen with no craters at all, a sign that the slowly churning ice keeps wiping the surface clean.

What memento of the man who discovered Pluto rides aboard New Horizons?

Some of his ashes ride in a small container fixed inside the probe, so the man who found Pluto in 1930 flew past it in 2015; the inscription remembers him as an astronomer, teacher, punster and friend.

New Horizons is comparable in size and shape to which musical instrument?

A grand piano is the mission's own comparison: fully fuelled, the probe weighed just 478 kg at launch, and it does its work on less power than a pair of 100-watt light bulbs.

Arrokoth, which New Horizons flew past on New Year's Day 2019, turned out to be shaped like what?

A snowman of two lobes that were once separate bodies, which circled each other ever more closely and gently merged; NASA called the shape, unlike any seen before, the biggest surprise of the flyby.

What was Arrokoth's public-vote nickname before it was formally named?

The choice was criticised for the term's use by 19th-century occultists and Nazi-era mystics, and the object was renamed after a Powhatan word.

Since its discovery in 1930, Pluto has yet to do what?

Finish one lap of the Sun: a single Pluto year lasts 248 of ours, so the first full circuit since its discovery will not be complete until 2178.

How was Arrokoth found in 2014 as a potential New Horizons target?

Using the Hubble Space Telescope was the fallback: from 2011 the team had searched with some of the largest telescopes on the ground and found nothing the probe had the fuel to reach.

The hypothetical Planet Nine was proposed to explain what oddity among extreme trans-Neptunian objects?

The clustering of their orbits struck two Caltech astronomers in 2016: six of the most distant known bodies all swing out the same way, a line-up they gave a 0.007% chance of being a fluke, though sceptics suspect biased surveys.

New Horizons set which record at its launch in 2006?

Fastest launch of any spacecraft: it crossed the Moon's orbit just nine hours after liftoff, yet Pluto is so remote that the trip there took another nine and a half years.

Pluto was discovered in 1930 from the observatory Percival Lowell built in which US state?

Arizona is where Percival Lowell built his private observatory to study what he took for canals on Mars; the hunt he began there for a planet beyond Neptune found Pluto in 1930, years after his death.

Which body is the only dwarf planet orbiting between Mars and Jupiter instead of out beyond Neptune?

Ceres was taken for a missing planet in 1801, then classed as an asteroid once similar bodies turned up; the 2006 ruling that demoted Pluto promoted it to dwarf planet.

Which mythical hybrids give their name to the comet-like bodies between Jupiter and Neptune?

Centaurs, half horse and half human in myth, suit bodies that behave as both asteroid and comet; the giant planets' gravity makes their paths so unstable that fresh ones must keep arriving from beyond Neptune.

Which icy body found among the giant planets in 1977 is named for Achilles' wise tutor?

Chiron was filed as an asteroid until a comet-like haze appeared around it in 1989; its unstable path was the first sign that such bodies are short-lived strays, resupplied from farther out.