50 Fun Facts About Kuiper Belt

The Kuiper Belt extends from Neptune's orbit at 30 AU out to roughly how far from the Sun?

Its inner edge is Neptune's orbit, and the whole thing is about twenty times as wide as the asteroid belt.

Compared with the asteroid belt, roughly how much wider is the Kuiper Belt?

It is also somewhere between 20 and 200 times as massive.

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

At the belt's temperature of only about 50 K, compounds that would be gases nearer the Sun stay frozen solid.

The belt is named after which Dutch astronomer, who speculated about such a disc in 1951?

He is often called the father of modern planetary science, and had eyesight sharp enough to see magnitude 7.5 stars unaided.

Which Irish army officer and amateur astronomer proposed a disc of bodies beyond Neptune in the 1930s and 1940s, giving the belt its alternative name?

He argued the outer solar nebula was too thinly spread to form planets, so it condensed into 'a very large number of comparatively small bodies'.

According to David Jewitt, which Uruguayan astronomer 'most nearly deserves the credit' for predicting the belt with his 1980 comet-belt paper?

He calculated that for every short-period comet the Oort cloud sent inward, 600 would have to be flung into interstellar space.

Ironically, Kuiper's own 1951 idea assumed what about Pluto that would have meant no belt exists today?

Astronomers then thought Pluto was roughly Earth-mass; Charon's discovery in 1978 showed it was only 0.2% of that.

Which two astronomers announced the first modern Kuiper Belt object, 1992 QB1, after a five-year search?

Jewitt had told his graduate student, 'If we don't, nobody will'; the pair later shared the 2012 Kavli Prize.

What name did 1992 QB1 finally receive in 2018?

Its discoverers wanted 'Smiley', but that was taken by an asteroid, so it was named for the primeval man of William Blake's mythology.

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

IAU rules say classical objects must be named for mythological beings associated with creation.

Jane Luu, co-discoverer of the first Kuiper Belt object, came to the United States in 1975 as a refugee from which country?

She graduated as her high school's valedictorian and studied physics at Stanford before joining Jewitt at MIT.

Which device, used to spot moving objects between paired photographs, did both Pluto's discoverer and the Kuiper Belt searchers rely on?

Examining one pair of plates took Jewitt and Luu about eight hours until CCDs let them blink images on a computer screen.

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

Over a thousand were actually found in the twenty years after 1992 QB1.

Which region, not the Kuiper Belt proper, is now thought to be the true source of short-period comets?

Neptune's outward migration 4.5 billion years ago left it as a dynamically active zone whose objects it can still disturb.

How much more distant than the Kuiper Belt is the hypothesised Oort cloud thought to be?

Unlike the belt, the Oort cloud is believed to be mostly spherical and is the source of long-period comets.

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

About 200 are known; IAU rules say all of them must be named for underworld deities.

What is the nickname for objects in the sparsely populated 1:2 resonance with Neptune at about 47.7 AU?

They complete half an orbit for every one of Neptune's.

What is the 'Kuiper cliff'?

Models predicted large objects should double beyond 50 AU; the falloff is real, unexplained, and one suggested cause is an unseen planet.

Overall, the Kuiper Belt is described as more resembling what shape than a belt?

Its main concentration extends up to ten degrees outside the ecliptic plane, with a more diffuse spread further out.

The 'dynamically cold' and 'dynamically hot' populations of the classical belt are named by analogy to what?

The cold group has near-circular, low-inclination orbits, is redder and brighter, and has more binaries; the hot group is inclined by up to 30 degrees.

A 2014 estimate put the total mass of the Kuiper Belt at roughly how many Earth masses?

That small mass puzzles modellers, because building objects over 100 km across by collisions needs far more material.

Which popular account of giant-planet migration, named after a French city, reproduces much of the belt's structure?

In it, a Jupiter-Saturn 1:2 resonance flings Uranus and Neptune outward through the primordial disc, ejecting 99% of the belt's original population.

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

It is only 14% larger than Pluto and its surface is made of similar ices; it may have been captured while part of a binary.

Which of Saturn's moons, like Neptune's largest moon, may have originated in the Kuiper Belt?

Both are listed as possible immigrants from the region in the belt's encyclopaedia entry.

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

He was 23 when the Lowell Observatory director gave him the job of hunting Planet X.

In what year did the International Astronomical Union redefine 'planet' and reclassify Pluto as a dwarf planet?

The new rule that a planet must have 'cleared the neighbourhood around its orbit' was the sticking point, since Pluto shares its orbit with many sizeable bodies.

How many known moons does Pluto have?

Charon is over half Pluto's diameter, so the pair's centre of mass lies outside either body and they are sometimes called a binary.

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

Its eccentric orbit swings between 30 and 49 AU, sometimes bringing it closer to the Sun than Neptune.

Which object beyond the belt, discovered in 2005 and 27% more massive than Pluto, forced the IAU to define what a planet is?

NASA initially called it the tenth planet; a 2010 stellar occultation showed it is actually slightly smaller than Pluto by volume.

Eris is named after the Greco-Roman goddess of what?

Its moon Dysnomia is named for the daimon of lawlessness, and the pair were long the most distant known natural objects in the Solar System.

Which Caltech astronomer led the Palomar team that discovered Eris, Makemake and (disputedly) Haumea?

Eris and Makemake were both announced on 29 July 2005, two days after Haumea, amid a priority dispute with a Spanish team.

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

Its two moons are Hi'iaka and Namaka, and its elongated shape spins fast enough to have rings and a collisional family.

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

Its shape is thought to be a Jacobi ellipsoid, with a long axis twice the length of its short one.

Makemake's diameter is roughly what fraction of Pluto's?

Its highly reflective surface is largely frozen methane stained reddish-brown by tholins, and it has one unnamed moon.

Quaoar defies theoretical expectations by having two thin rings where?

Rings that far out should be unstable; its elongated shape, its moon and extreme cold may keep them intact.

Roughly how long does Sedna take to complete one orbit of the Sun?

Its aphelion lies 937 AU out, about 19 times farther than Pluto's, and some call it the first known inner Oort cloud object.

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

At about 1,230 km across it is similar in size to Charon, and it sits in a 3:10 resonance with Neptune.

New Horizons, the first spacecraft to explore the Kuiper Belt, flew past Pluto on 14 July of which year?

Launched in 2006, it left Earth faster than any human-made object before it, at 16.26 km/s.

What unusual cargo does New Horizons carry to commemorate Pluto's discoverer?

Also aboard are a Florida state quarter and a Maryland quarter, officially listed as trim weights.

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

One description had it as 'a piano glued to a cocktail bar-sized satellite dish'.

On 1 January 2019 New Horizons flew past Arrokoth, which became the farthest object ever visited by a spacecraft. What shape is it?

Its lobes, Wenu and Weeyo, were once separate bodies that gently merged; the surface is red and barely cratered.

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.

How long is Arrokoth?

New Horizons found it 32 km long by 16 km wide, and the Ralph instrument confirmed its red colour.

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

Marc Buie and the search team first logged it as 1110113Y, then 'Potential Target 1'.

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

They tend to reach perihelion in one sector with similar tilts, though sceptics blame observational bias.

Roughly what fraction of Kuiper Belt objects are estimated to exist as binaries?

Pluto and Charon are the most famous pair, and the six largest trans-Neptunian objects all have satellites.

By 2006 astronomers had resolved Kuiper-Belt-like dust discs around how many stars other than the Sun?

Roughly 15 to 20 percent of Sun-like stars show an infrared excess hinting at massive belts of their own.

Roughly what is the temperature of the Kuiper Belt?

That cold keeps methane, ammonia and water frozen solid where they would be gases nearer the Sun.

What are the comet-like bodies that orbit between Jupiter and Neptune called?

Their orbits are unstable over a few million years, so they must be replenished from an outer reservoir.

Which object, found in 1977, first hinted at an outer reservoir replenishing the unstable Jupiter–Neptune bodies?

Pholus followed in 1992, the same year the first modern Kuiper Belt object was found.