Kuiper belt (/ˈkaɪpər/ or Dutch pronunciation:
['kœy̯pər]), occasionally called the Edgeworth–Kuiper belt, is
a circumstellar disc in the outer Solar System, extending from the
Neptune (at 30 AU) to approximately 50 AU from the Sun. It
is similar to the asteroid belt, but is far larger—20 times as wide
and 20 to 200 times as massive. Like the asteroid belt, it
consists mainly of small bodies or remnants from when the Solar System
formed. While many asteroids are composed primarily of rock and metal,
Kuiper belt objects are composed largely of frozen volatiles
(termed "ices"), such as methane, ammonia and water. The Kuiper belt
is home to three officially recognized dwarf planets: Pluto, Haumea
and Makemake. Some of the Solar System's moons, such as Neptune's
Triton and Saturn's Phoebe, may have originated in the region.
Kuiper belt was named after Dutch-American astronomer Gerard
Kuiper, though he did not predict its existence. In 1992, Albion was
discovered, the first
Kuiper belt object (KBO) since
Charon. Since its discovery, the number of known KBOs has increased
to over a thousand, and more than 100,000 KBOs over 100 km
(62 mi) in diameter are thought to exist. The
Kuiper belt was
initially thought to be the main repository for periodic comets, those
with orbits lasting less than 200 years. Studies since the mid-1990s
have shown that the belt is dynamically stable and that comets' true
place of origin is the scattered disc, a dynamically active zone
created by the outward motion of
Neptune 4.5 billion years
ago; scattered disc objects such as Eris have extremely eccentric
orbits that take them as far as 100 AU from the Sun.[nb 1]
Kuiper belt is distinct from the theoretical Oort cloud, which is
a thousand times more distant and is mostly spherical. The objects
within the Kuiper belt, together with the members of the scattered
disc and any potential
Hills cloud or
Oort cloud objects, are
collectively referred to as trans-Neptunian objects (TNOs). Pluto
is the largest and most massive member of the Kuiper belt, and the
largest and the second-most-massive known TNO, surpassed only by Eris
in the scattered disc.[nb 1] Originally considered a planet, Pluto's
status as part of the
Kuiper belt caused it to be reclassified as a
dwarf planet in 2006. It is compositionally similar to many other
objects of the
Kuiper belt and its orbital period is characteristic of
a class of KBOs, known as "plutinos", that share the same 2:3
resonance with Neptune.
2.1 Classical belt
2.3 Kuiper cliff
Mass and size distribution
6 Scattered objects
7 Largest KBOs
9 Extrasolar Kuiper belts
10 See also
13 External links
After the discovery of
Pluto in 1930, many speculated that it might
not be alone. The region now called the
Kuiper belt was hypothesized
in various forms for decades. It was only in 1992 that the first
direct evidence for its existence was found. The number and variety of
prior speculations on the nature of the
Kuiper belt have led to
continued uncertainty as to who deserves credit for first proposing
The first astronomer to suggest the existence of a trans-Neptunian
population was Frederick C. Leonard. Soon after Pluto's discovery by
Clyde Tombaugh in 1930, Leonard pondered whether it was "not likely
Pluto there has come to light the first of a series of
ultra-Neptunian bodies, the remaining members of which still await
discovery but which are destined eventually to be detected". That
same year, astronomer Armin O. Leuschner suggested that
Pluto "may be
one of many long-period planetary objects yet to be discovered."
Astronomer Gerard Kuiper, after whom the
Kuiper belt is named
In 1943, in the Journal of the British Astronomical Association,
Kenneth Edgeworth hypothesized that, in the region beyond Neptune, the
material within the primordial solar nebula was too widely spaced to
condense into planets, and so rather condensed into a myriad of
smaller bodies. From this he concluded that "the outer region of the
solar system, beyond the orbits of the planets, is occupied by a very
large number of comparatively small bodies" and that, from time to
time, one of their number "wanders from its own sphere and appears as
an occasional visitor to the inner solar system", becoming a
In 1951, in a paper in Astrophysics: A Topical Symposium, Gerard
Kuiper speculated on a similar disc having formed early in the Solar
System's evolution, but he did not think that such a belt still
existed today. Kuiper was operating on the assumption, common in his
Pluto was the size of
Earth and had therefore scattered
these bodies out toward the
Oort cloud or out of the Solar System.
Were Kuiper's hypothesis correct, there would not be a Kuiper belt
The hypothesis took many other forms in the following decades. In
1962, physicist Al G.W. Cameron postulated the existence of "a
tremendous mass of small material on the outskirts of the solar
system". In 1964, Fred Whipple, who popularised the famous "dirty
snowball" hypothesis for cometary structure, thought that a "comet
belt" might be massive enough to cause the purported discrepancies in
the orbit of
Uranus that had sparked the search for
Planet X, or, at
the very least, massive enough to affect the orbits of known
comets. Observation ruled out this hypothesis.
Charles Kowal discovered 2060 Chiron, an icy planetoid with
an orbit between
Saturn and Uranus. He used a blink comparator, the
same device that had allowed
Clyde Tombaugh to discover
50 years before. In 1992, another object, 5145 Pholus, was
discovered in a similar orbit. Today, an entire population of
comet-like bodies, called the centaurs, is known to exist in the
Jupiter and Neptune. The centaurs' orbits are unstable
and have dynamical lifetimes of a few million years. From the time
of Chiron's discovery in 1977, astronomers have speculated that the
centaurs therefore must be frequently replenished by some outer
Further evidence for the existence of the
Kuiper belt later emerged
from the study of comets. That comets have finite lifespans has been
known for some time. As they approach the Sun, its heat causes their
volatile surfaces to sublimate into space, gradually dispersing them.
In order for comets to continue to be visible over the age of the
Solar System, they must be replenished frequently. One such area
of replenishment is the Oort cloud, a spherical swarm of comets
extending beyond 50,000 AU from the
Sun first hypothesised by Dutch
Jan Oort in 1950. The
Oort cloud is thought to be the
point of origin of long-period comets, which are those, like
Hale–Bopp, with orbits lasting thousands of years.
There is another comet population, known as short-period or periodic
comets, consisting of those comets that, like Halley's Comet, have
orbital periods of less than 200 years. By the 1970s, the rate at
which short-period comets were being discovered was becoming
increasingly inconsistent with their having emerged solely from the
Oort cloud. For an
Oort cloud object to become a short-period
comet, it would first have to be captured by the giant planets. In a
paper published in Monthly Notices of the Royal Astronomical Society
in 1980, Uruguayan astronomer Julio Fernández stated that for every
short-period comet to be sent into the inner
Solar System from the
Oort cloud, 600 would have to be ejected into interstellar space. He
speculated that a comet belt from between 35 and 50 AU would be
required to account for the observed number of comets. Following
up on Fernández's work, in 1988 the Canadian team of Martin Duncan,
Tom Quinn and
Scott Tremaine ran a number of computer simulations to
determine if all observed comets could have arrived from the Oort
cloud. They found that the
Oort cloud could not account for all
short-period comets, particularly as short-period comets are clustered
near the plane of the Solar System, whereas Oort-cloud comets tend to
arrive from any point in the sky. With a "belt", as Fernández
described it, added to the formulations, the simulations matched
observations. Reportedly because the words "Kuiper" and "comet
belt" appeared in the opening sentence of Fernández's paper, Tremaine
named this hypothetical region the "Kuiper belt".
The array of telescopes atop Mauna Kea, with which the
Kuiper belt was
In 1987, astronomer David Jewitt, then at MIT, became increasingly
puzzled by "the apparent emptiness of the outer Solar System". He
encouraged then-graduate student
Jane Luu to aid him in his endeavour
to locate another object beyond Pluto's orbit, because, as he told
her, "If we don't, nobody will." Using telescopes at the Kitt Peak
National Observatory in Arizona and the Cerro Tololo Inter-American
Observatory in Chile, Jewitt and Luu conducted their search in much
the same way as
Clyde Tombaugh and
Charles Kowal had, with a blink
comparator. Initially, examination of each pair of plates took
about eight hours, but the process was sped up with the arrival of
electronic charge-coupled devices or CCDs, which, though their field
of view was narrower, were not only more efficient at collecting light
(they retained 90% of the light that hit them, rather than the 10%
achieved by photographs) but allowed the blinking process to be done
virtually, on a computer screen. Today, CCDs form the basis for most
astronomical detectors. In 1988, Jewitt moved to the Institute of
Astronomy at the University of Hawaii. Luu later joined him to work at
the University of Hawaii's 2.24 m telescope at Mauna Kea.
Eventually, the field of view for CCDs had increased to 1024 by 1024
pixels, which allowed searches to be conducted far more rapidly.
Finally, after five years of searching, Jewitt and Luu announced on
August 30, 1992 the "Discovery of the candidate
Kuiper belt object"
15760 Albion. Six months later, they discovered a second object in
the region, (181708) 1993 FW.
Studies conducted since the trans-Neptunian region was first charted
have shown that the region now called the
Kuiper belt is not the point
of origin of short-period comets, but that they instead derive from a
linked population called the scattered disc. The scattered disc was
Neptune migrated outward into the proto-Kuiper belt,
which at the time was much closer to the Sun, and left in its wake a
population of dynamically stable objects that could never be affected
by its orbit (the
Kuiper belt proper), and a population whose
perihelia are close enough that
Neptune can still disturb them as it
travels around the
Sun (the scattered disc). Because the scattered
disc is dynamically active and the
Kuiper belt relatively dynamically
stable, the scattered disc is now seen as the most likely point of
origin for periodic comets.
Astronomers sometimes use the alternative name Edgeworth–Kuiper belt
to credit Edgeworth, and KBOs are occasionally referred to as EKOs.
Brian G. Marsden claims that neither deserves true credit: "Neither
Edgeworth nor Kuiper wrote about anything remotely like what we are
now seeing, but
Fred Whipple did".
David Jewitt comments: "If
anything... Fernández most nearly deserves the credit for predicting
the Kuiper Belt."
KBOs are sometimes called "kuiperoids", a name suggested by Clyde
Tombaugh. The term "trans-Neptunian object" (TNO) is recommended
for objects in the belt by several scientific groups because the term
is less controversial than all others—it is not an exact synonym
though, as TNOs include all objects orbiting the
Sun past the orbit of
Neptune, not just those in the Kuiper belt.
Dust in the
Kuiper belt creates a faint infrared disc. (Click on the
"play" button to watch the video.)
At its fullest extent (but excluding the scattered disc), including
its outlying regions, the
Kuiper belt stretches from roughly 30 to 55
AU. The main body of the belt is generally accepted to extend from the
2:3 mean-motion resonance (see below) at 39.5 AU to the 1:2 resonance
at roughly 48 AU. The
Kuiper belt is quite thick, with the main
concentration extending as much as ten degrees outside the ecliptic
plane and a more diffuse distribution of objects extending several
times farther. Overall it more resembles a torus or doughnut than a
belt. Its mean position is inclined to the ecliptic by 1.86
The presence of
Neptune has a profound effect on the Kuiper belt's
structure due to orbital resonances. Over a timescale comparable to
the age of the Solar System, Neptune's gravity destabilises the orbits
of any objects that happen to lie in certain regions, and either sends
them into the inner
Solar System or out into the scattered disc or
interstellar space. This causes the
Kuiper belt to have pronounced
gaps in its current layout, similar to the Kirkwood gaps in the
asteroid belt. In the region between 40 and 42 AU, for instance, no
objects can retain a stable orbit over such times, and any observed in
that region must have migrated there relatively recently.
Classical Kuiper belt
Classical Kuiper belt object
Between the 2:3 and 1:2 resonances with Neptune, at approximately
42–48 AU, the gravitational interactions with
over an extended timescale, and objects can exist with their orbits
essentially unaltered. This region is known as the classical Kuiper
belt, and its members comprise roughly two thirds of KBOs observed to
date. Because the first modern KBO discovered, (15760) 1992
QB1, is considered the prototype of this group, classical KBOs are
often referred to as cubewanos ("Q-B-1-os"). The guidelines
established by the
IAU demand that classical KBOs be given names of
mythological beings associated with creation.
Kuiper belt appears to be a composite of two separate
populations. The first, known as the "dynamically cold" population,
has orbits much like the planets; nearly circular, with an orbital
eccentricity of less than 0.1, and with relatively low inclinations up
to about 10° (they lie close to the plane of the
Solar System rather
than at an angle). The cold population also contain a concentration of
objects, referred to as the kernel, with semi-major axes at 44–44.5
AU. The second, the "dynamically hot" population, has orbits much
more inclined to the ecliptic, by up to 30°. The two populations have
been named this way not because of any major difference in
temperature, but from analogy to particles in a gas, which increase
their relative velocity as they become heated up. Not only are the
two populations in different orbits, the cold population also differs
in color and albedo, being redder and brighter, has a larger fraction
of binary objects, has a different size distribution, and
lacks very large objects. The difference in colors may be a
reflection of different compositions, which suggests they formed in
different regions. The hot population is proposed to have formed near
Neptune's original orbit and to have been scattered out during the
migration of the giant planets. The cold population, on the
other hand, has been proposed to have formed more or less in its
current position because the loose binaries would be unlikely to
survive encounters with Neptune. Although the
Nice model appears
to be able to at least partially explain a compositional difference,
it has also been suggested the color difference may reflect
differences in surface evolution.
Main article: Resonant trans-Neptunian object
Distribution of cubewanos (blue), Resonant trans-Neptunian objects
(red), Sednoids (yellow) and scattered objects (grey)
Orbit classification (schematic of semi-major axes)
When an object's orbital period is an exact ratio of Neptune's (a
situation called a mean-motion resonance), then it can become locked
in a synchronised motion with
Neptune and avoid being perturbed away
if their relative alignments are appropriate. If, for instance, an
object orbits the
Sun twice for every three
Neptune orbits, and if it
reaches perihelion with
Neptune a quarter of an orbit away from it,
then whenever it returns to perihelion,
Neptune will always be in
about the same relative position as it began, because it will have
completed 1 1⁄2 orbits in the same time. This is known as
the 2:3 (or 3:2) resonance, and it corresponds to a characteristic
semi-major axis of about 39.4 AU. This 2:3 resonance is populated
by about 200 known objects, including
Pluto together with its
moons. In recognition of this, the members of this family are known as
plutinos. Many plutinos, including Pluto, have orbits that cross that
of Neptune, though their resonance means they can never collide.
Plutinos have high orbital eccentricities, suggesting that they are
not native to their current positions but were instead thrown
haphazardly into their orbits by the migrating Neptune. IAU
guidelines dictate that all plutinos must, like Pluto, be named for
underworld deities. The 1:2 resonance (whose objects complete half
an orbit for each of Neptune's) corresponds to semi-major axes of
~47.7AU, and is sparsely populated. Its residents are sometimes
referred to as twotinos. Other resonances also exist at 3:4, 3:5, 4:7
Neptune has a number of trojan objects, which occupy its
Lagrangian points, gravitationally stable regions leading and trailing
it in its orbit.
Neptune trojans are in a 1:1 mean-motion resonance
Neptune and often have very stable orbits.
Additionally, there is a relative absence of objects with semi-major
axes below 39 AU that cannot apparently be explained by the present
resonances. The currently accepted hypothesis for the cause of this is
Neptune migrated outward, unstable orbital resonances moved
gradually through this region, and thus any objects within it were
swept up, or gravitationally ejected from it.
Histogram of the semi-major axes of
Kuiper belt objects with
inclinations above and below 5 degrees. Spikes from the plutinos
and the ‘kernel’ are visible at 39–40 AU and 44 AU.
The 1:2 resonance appears to be an edge beyond which few objects are
known. It is not clear whether it is actually the outer edge of the
classical belt or just the beginning of a broad gap. Objects have been
detected at the 2:5 resonance at roughly 55 AU, well outside
the classical belt; predictions of a large number of bodies in
classical orbits between these resonances have not been verified
Based on estimations of the primordial mass required to form Uranus
and Neptune, as well as bodies as large as
Pluto (see below), earlier
models of the
Kuiper belt had suggested that the number of large
objects would increase by a factor of two beyond 50 AU, so
this sudden drastic falloff, known as the Kuiper cliff, was
unexpected, and to date its cause is unknown. In 2003, Bernstein,
Trilling, et al. found evidence that the rapid decline in objects of
100 km or more in radius beyond 50 AU is real, and not due
to observational bias. Possible explanations include that material at
that distance was too scarce or too scattered to accrete into large
objects, or that subsequent processes removed or destroyed those that
did. Patryk Lykawka of
Kobe University claimed that the
gravitational attraction of an unseen large planetary object, perhaps
the size of
Earth or Mars, might be responsible.
Simulation showing outer planets and Kuiper belt: a) before
Saturn 1:2 resonance, b) scattering of
Kuiper belt objects
Solar System after the orbital shift of Neptune, c) after
Kuiper belt bodies by Jupiter
The precise origins of the
Kuiper belt and its complex structure are
still unclear, and astronomers are awaiting the completion of several
wide-field survey telescopes such as
Pan-STARRS and the future LSST,
which should reveal many currently unknown KBOs. These surveys will
provide data that will help determine answers to these questions.
Kuiper belt is thought to consist of planetesimals, fragments from
the original protoplanetary disc around the
Sun that failed to fully
coalesce into planets and instead formed into smaller bodies, the
largest less than 3,000 kilometres (1,900 mi) in diameter.
Studies of the crater counts on
Pluto and Charon revealed a scarcity
of small craters suggesting that such objects formed directly as
sizeable objects in the range of tens of kilometers in diameter rather
than being accreted from much smaller, roughly kilometer scale
bodies. Hypothetical mechanisms for the formation of these larger
bodies include the gravitational collapse of clouds of pebbles
concentrated between eddies in a turbulent protoplanetary disk
or in streaming instabilities. These collapsing clouds may
fragment, forming binaries.
Modern computer simulations show the
Kuiper belt to have been strongly
Jupiter and Neptune, and also suggest that neither
Neptune could have formed in their present positions,
because too little primordial matter existed at that range to produce
objects of such high mass. Instead, these planets are estimated to
have formed closer to Jupiter. Scattering of planetesimals early in
the Solar System's history would have led to migration of the orbits
of the giant planets: Saturn, Uranus, and
Neptune drifted outwards,
Jupiter drifted inwards. Eventually, the orbits shifted to the
Saturn reached an exact 1:2 resonance; Jupiter
Sun twice for every one
Saturn orbit. The gravitational
repercussions of such a resonance ultimately destabilized the orbits
Uranus and Neptune, causing them to be scattered outward onto
high-eccentricity orbits that crossed the primordial planetesimal
disc. While Neptune's orbit was highly eccentric, its
mean-motion resonances overlapped and the orbits of the planetesimals
evolved chaotically, allowing planetesimals to wander outward as far
as Neptune's 1:2 resonance to form a dynamically cold belt of
low-inclination objects. Later, after its eccentricity decreased,
Neptune's orbit expanded outward toward its current position. Many
planetesimals were captured into and remain in resonances during this
migration, others evolved onto higher-inclination and
lower-eccentricity orbits and escaped from the resonances onto stable
orbits. Many more planetesimals were scattered inward, with small
fractions being captured as
Jupiter trojans, as irregular satellites
orbiting the giant planets, and as outer belt asteroids. The remainder
were scattered outward again by
Jupiter and in most cases ejected from
Solar System reducing the primordial
Kuiper belt population by 99%
The original version of the currently most popular model, the "Nice
model", reproduces many characteristics of the
Kuiper belt such as the
"cold" and "hot" populations, resonant objects, and a scattered disc,
but it still fails to account for some of the characteristics of their
distributions. The model predicts a higher average eccentricity in
classical KBO orbits than is observed (0.10–0.13 versus 0.07) and
its predicted inclination distribution contains too few high
inclination objects. In addition, the frequency of binary objects
in the cold belt, many of which are far apart and loosely bound, also
poses a problem for the model. These are predicted to have been
separated during encounters with Neptune, leading some to propose
that the cold disc formed at its current location, representing the
only truly local population of small bodies in the solar system.
A recent modification of the
Nice model has the
Solar System begin
with five giant planets, including an additional ice giant, in a chain
of mean-motion resonances. About 400 million years after the formation
Solar System the resonance chain is broken. Instead of being
scattered into the disc, the ice giants first migrate outward several
AU. This divergent migration eventually leads to a resonance
crossing, destabilizing the orbits of the planets. The extra ice giant
Saturn and is scattered inward onto a Jupiter-crossing
orbit and after a series of encounters is ejected from the Solar
System. The remaining planets then continue their migration until the
planetesimal disc is nearly depleted with small fractions remaining in
As in the original Nice model, objects are captured into resonances
Neptune during its outward migration. Some remain in the
resonances, others evolve onto higher-inclination, lower-eccentricity
orbits, and are released onto stable orbits forming the dynamically
hot classical belt. The hot belt's inclination distribution can be
Neptune migrated from 24 AU to 30 AU on a 30 Myr
Neptune migrates to 28 AU, it has a gravitational
encounter with the extra ice giant. Objects captured from the cold
belt into the 1:2 mean-motion resonance with
Neptune are left behind
as a local concentration at 44 AU when this encounter causes Neptune's
semi-major axis to jump outward. The objects deposited in the cold
belt include some loosely bound 'blue' binaries originating from
closer than the cold belt's current location. If Neptune's
eccentricity remains small during this encounter, the chaotic
evolution of orbits of the original
Nice model is avoided and a
primordial cold belt is preserved. In the later phases of
Neptune's migration, a slow sweeping of mean-motion resonances removes
the higher-eccentricity objects from the cold belt, truncating its
The infrared spectra of both Eris and Pluto, highlighting their common
methane absorption lines
Being distant from the
Sun and major planets,
Kuiper belt objects are
thought to be relatively unaffected by the processes that have shaped
and altered other
Solar System objects; thus, determining their
composition would provide substantial information on the makeup of the
earliest Solar System. Due to their small size and extreme
distance from Earth, the chemical makeup of KBOs is very difficult to
determine. The principal method by which astronomers determine the
composition of a celestial object is spectroscopy. When an object's
light is broken into its component colors, an image akin to a rainbow
is formed. This image is called a spectrum. Different substances
absorb light at different wavelengths, and when the spectrum for a
specific object is unravelled, dark lines (called absorption lines)
appear where the substances within it have absorbed that particular
wavelength of light. Every element or compound has its own unique
spectroscopic signature, and by reading an object's full spectral
"fingerprint", astronomers can determine its composition.
Analysis indicates that
Kuiper belt objects are composed of a mixture
of rock and a variety of ices such as water, methane, and ammonia. The
temperature of the belt is only about 50 K, so many compounds that
would be gaseous closer to the
Sun remain solid. The densities and
rock–ice fractions are known for only a small number of objects for
which the diameters and the masses have been determined. The diameter
can be determined by imaging with a high-resolution telescope such as
the Hubble Space Telescope, by the timing of an occultation when an
object passes in front of a star or, most commonly, by using the
albedo of an object calculated from its infrared emissions. The masses
are determined using the semi-major axes and periods of satellites,
which are therefore known only for a few binary objects. The densities
range from less than 0.4 to 2.6 g/cm3. The least dense objects are
thought to be largely composed of ice and have significant porosity.
The densest objects are likely composed of rock with a thin crust of
ice. There is a trend of low densities for small objects and high
densities for the largest objects. One possible explanation for this
trend is that ice was lost from the surface layers when differentiated
objects collided to form the largest objects.
Initially, detailed analysis of KBOs was impossible, and so
astronomers were only able to determine the most basic facts about
their makeup, primarily their color. These first data showed a
broad range of colors among KBOs, ranging from neutral grey to deep
red. This suggested that their surfaces were composed of a wide
range of compounds, from dirty ices to hydrocarbons. This
diversity was startling, as astronomers had expected KBOs to be
uniformly dark, having lost most of the volatile ices from their
surfaces to the effects of cosmic rays. Various solutions were
suggested for this discrepancy, including resurfacing by impacts or
outgassing. Jewitt and Luu's spectral analysis of the known Kuiper
belt objects in 2001 found that the variation in color was too extreme
to be easily explained by random impacts. The radiation from the
Sun is thought to have chemically altered methane on the surface of
KBOs, producing products such as tholins.
Makemake has been shown to
possess a number of hydrocarbons derived from the radiation-processing
of methane, including ethane, ethylene and acetylene.
Although to date most KBOs still appear spectrally featureless due to
their faintness, there have been a number of successes in determining
their composition. In 1996, Robert H. Brown et al. acquired
spectroscopic data on the KBO 1993 SC, which revealed that its surface
composition is markedly similar to that of Pluto, as well as Neptune's
moon Triton, with large amounts of methane ice. For the smaller
objects, only colors and in some cases the albedos have been
determined. These objects largely fall into two classes: gray with low
albedos, or very red with higher albedos. The difference in colors and
albedos is hypothesized to be due to the retention or the loss of
hydrogen sulfide (H2S) on the surface of these objects, with the
surfaces of those that formed far enough from the
Sun to retain H2S
being reddened due to irradiation.
The largest KBOs, such as
Pluto and Quaoar, have surfaces rich in
volatile compounds such as methane, nitrogen and carbon monoxide; the
presence of these molecules is likely due to their moderate vapor
pressure in the 30–50 K temperature range of the Kuiper belt.
This allows them to occasionally boil off their surfaces and then fall
again as snow, whereas compounds with higher boiling points would
remain solid. The relative abundances of these three compounds in the
largest KBOs is directly related to their surface gravity and ambient
temperature, which determines which they can retain.
Water ice has
been detected in several KBOs, including members of the
such as 1996 TO66, mid-sized objects such as
38628 Huya and 20000
Varuna, and also on some small objects. The presence of
crystalline ice on large and mid-sized objects, including 50000 Quaoar
where ammonia hydrate has also been detected, may indicate past
tectonic activity aided by melting point lowering due to the presence
Mass and size distribution
Illustration of the power law
Despite its vast extent, the collective mass of the
Kuiper belt is
relatively low. The total mass is estimated to range between 1/25 and
1/10 the mass of the Earth. Conversely, models of the Solar
System's formation predict a collective mass for the
Kuiper belt of 30
Earth masses. This missing >99% of the mass can hardly be
dismissed, because it is required for the accretion of any KBOs larger
than 100 km (62 mi) in diameter. If the
Kuiper belt had
always had its current low density, these large objects simply could
not have formed by the collision and mergers of smaller
planetesimals. Moreover, the eccentricity and inclination of
current orbits makes the encounters quite "violent" resulting in
destruction rather than accretion. It appears that either the current
residents of the
Kuiper belt have been created closer to the Sun, or
some mechanism dispersed the original mass. Neptune's current
influence is too weak to explain such a massive "vacuuming", though
Nice model proposes that it could have been the cause of mass
removal in the past. Although the question remains open, the
conjectures vary from a passing star scenario to grinding of smaller
objects, via collisions, into dust small enough to be affected by
solar radiation. The extent of mass loss by collisional grinding
is limited by the presence of loosely bound binaries in the cold disk,
which are likely to be disrupted in collisions.
Bright objects are rare compared with the dominant dim population, as
expected from accretion models of origin, given that only some objects
of a given size would have grown further. This relationship between
N(D) (the number of objects of diameter greater than D) and D,
referred to as brightness slope, has been confirmed by observations.
The slope is inversely proportional to some power of the diameter D:
displaystyle frac dN dD propto D^ -q
where the current measures give q = 4 ±0.5.
This implies (assuming q is not 1) that
displaystyle Npropto D^ 1-q + text a constant .
(The constant may be non-zero only if the power law doesn't apply at
high values of D.)
Less formally, if q is 4, for example, there are 8 (=23) times more
objects in the 100–200 km range than in the 200–400 km
range, and for every object with a diameter between 1000 and
1010 km there should be around 1000 (=103) objects with diameter
of 100 to 101 km.
If q was 1 or less, the law would imply an infinite number and mass of
large objects in the Kuiper belt. If 1<q≤4 there will be a finite
number of objects greater than a given size, but the expected value of
their combined mass would be infinite. If q is 4 or more, the law
would imply an infinite mass of small objects. More accurate models
find that the "slope" parameter q is in effect greater at large
diameters and lesser at small diameters. It seems that
somewhat unexpectedly large, having several percent of the total mass
of the Kuiper belt. It is not expected that anything larger than Pluto
exists in the Kuiper belt, and in fact most of the brightest (largest)
objects at inclinations less than 5° have probably been found.
For most TNOs, only the absolute magnitude is actually known, the size
is inferred assuming a given albedo (not a safe assumption for larger
Recent research has revealed that the size distributions of the hot
classical and cold classical objects have differing slopes. The slope
for the hot objects is q = 5.3 at large diameters and q = 2.0 at small
diameters with the change in slope at 110 km. The slope for the
cold objects is q = 8.2 at large diameters and q = 2.9 at small
diameters with a change in slope at 140 km. The size
distributions of the scattering objects, the plutinos, and the Neptune
trojans have slopes similar to the other dynamically hot populations,
but may instead have a divot, a sharp decrease in the number of
objects below a specific size. This divot is hypothesized to be due to
either the collisional evolution of the population, or to be due to
the population having formed with no objects below this size, with the
smaller objects being fragments of the original objects.
As of December 2009, the smallest
Kuiper belt object detected is
980 m across. It is too dim (magnitude 35) to be seen by Hubble
directly, but it was detected by Hubble's star tracking system when it
occulted a star.
Comparison of the orbits of scattered disc objects (black), classical
KBOs (blue), and 2:5 resonant objects (green). Orbits of other KBOs
are gray. (Orbital axes have been aligned for comparison.)
Scattered disc and Centaur (minor planet)
The scattered disc is a sparsely populated region, overlapping with
Kuiper belt but extending to beyond 100 AU.
Scattered disc objects
(SDOs) have very elliptical orbits, often also very inclined to the
ecliptic. Most models of
Solar System formation show both KBOs and
SDOs first forming in a primordial belt, with later gravitational
interactions, particularly with Neptune, sending the objects outward,
some into stable orbits (the KBOs) and some into unstable orbits, the
scattered disc. Due to its unstable nature, the scattered disc is
suspected to be the point of origin of many of the Solar System's
short-period comets. Their dynamic orbits occasionally force them into
the inner Solar System, first becoming centaurs, and then short-period
According to the Minor
Planet Center, which officially catalogues all
trans-Neptunian objects, a KBO, strictly speaking, is any object that
orbits exclusively within the defined
Kuiper belt region regardless of
origin or composition. Objects found outside the belt are classed as
scattered objects. In some scientific circles the term "Kuiper
belt object" has become synonymous with any icy minor planet native to
Solar System assumed to have been part of that initial
class, even if its orbit during the bulk of
Solar System history has
been beyond the
Kuiper belt (e.g. in the scattered-disc region). They
often describe scattered disc objects as "scattered Kuiper belt
objects". Eris, which is known to be more massive than Pluto, is
often referred to as a KBO, but is technically an SDO. A consensus
among astronomers as to the precise definition of the
Kuiper belt has
yet to be reached, and this issue remains unresolved.
The centaurs, which are not normally considered part of the Kuiper
belt, are also thought to be scattered objects, the only difference
being that they were scattered inward, rather than outward. The Minor
Planet Center groups the centaurs and the SDOs together as scattered
Main article: Triton (moon)
Neptune's moon Triton
During its period of migration,
Neptune is thought to have captured a
large KBO, Triton, which is the only large moon in the Solar System
with a retrograde orbit (it orbits opposite to Neptune's rotation).
This suggests that, unlike the large moons of Jupiter,
Uranus, which are thought to have coalesced from rotating discs of
material around their young parent planets, Triton was a fully formed
body that was captured from surrounding space. Gravitational capture
of an object is not easy: it requires some mechanism to slow down the
object enough to be caught by the larger object's gravity. A possible
explanation is that Triton was part of a binary when it encountered
Neptune. (Many KBOs are members of binaries. See below.) Ejection of
the other member of the binary by
Neptune could then explain Triton's
capture. Triton is only 14% larger than Pluto, and spectral
analysis of both worlds shows that their surfaces are largely composed
of similar materials, such as methane and carbon monoxide. All this
points to the conclusion that Triton was once a KBO that was captured
Neptune during its outward migration.
See also: List of the brightest
Kuiper belt objects
Artistic comparison of Pluto, Eris, Makemake, Haumea, Sedna, 2002 MS4,
2007 OR10, Quaoar, Salacia, Orcus, and
Earth along with the Moon.
Since 2000, a number of KBOs with diameters of between 500 and
1,500 km (932 mi), more than half that of
2370 km), have been discovered. 50000 Quaoar, a classical KBO
discovered in 2002, is over 1,200 km across.
Makemake and Haumea,
both announced on July 29, 2005, are larger still. Other objects, such
28978 Ixion (discovered in 2001) and
20000 Varuna (discovered in
2000), measure roughly 500 km (311 mi) across.
Main article: Pluto
The discovery of these large KBOs in orbits similar to Pluto's led
many to conclude that, aside from its relative size,
Pluto was not
particularly different from other members of the Kuiper belt. Not only
are these objects similar to
Pluto in size, but many also have
satellites, and are of similar composition (methane and carbon
monoxide have been found both on
Pluto and on the largest KBOs).
Thus, just as Ceres was considered a planet before the discovery of
its fellow asteroids, some began to suggest that
Pluto might also be
The issue was brought to a head by the discovery of Eris, an object in
the scattered disc far beyond the Kuiper belt, that is now known to be
27% more massive than Pluto. (Eris was originally thought to be
Pluto by volume, but the
New Horizons mission found this
not to be the case.) In response, the International Astronomical Union
(IAU) was forced to define what a planet is for the first time, and in
so doing included in their definition that a planet must have "cleared
the neighbourhood around its orbit". As
Pluto shares its orbit
with many other sizable objects, it was deemed not to have cleared its
orbit, and was thus reclassified from a planet to a dwarf planet,
making it a member of the Kuiper belt.
Pluto is currently the largest known KBO, there is at least
one known larger object currently outside the
Kuiper belt that
probably originated in it: Neptune's moon Triton (which, as explained
above, is probably a captured KBO).
As of 2008, only five objects in the
Solar System (Ceres, Eris, and
the KBOs Pluto,
Makemake and Haumea) are listed as dwarf planets by
the IAU. 90482 Orcus,
28978 Ixion and many other Kuiper-belt objects
are large enough to be in hydrostatic equilibrium; most of them will
probably qualify when more is known about them.
The six largest TNOs (Eris, Pluto, 2007 OR10, Makemake,
Quaoar) are all known to have satellites, and two have more than one.
A higher percentage of the larger KBOs have satellites than the
smaller objects in the Kuiper belt, suggesting that a different
formation mechanism was responsible. There are also a high number
of binaries (two objects close enough in mass to be orbiting "each
other") in the Kuiper belt. The most notable example is the
Pluto–Charon binary, but it is estimated that around 11% of KBOs
exist in binaries.
Main article: New Horizons
Kuiper belt object—possible target of
New Horizons spacecraft
2014 MU69 (green circles), the selected target for the New
Kuiper belt object mission
Diagram showing the location of
2014 MU69 and trajectory for
On January 19, 2006, the first spacecraft to explore the Kuiper belt,
New Horizons, was launched, which flew by
Pluto on July 14, 2015.
Pluto flyby, the mission's goal was to locate and
investigate other, farther objects in the Kuiper belt.
On October 15, 2014, it was revealed that Hubble had uncovered three
potential targets, provisionally designated
PT1 ("potential target 1"), PT2 and PT3 by the
New Horizons team. The
objects' diameters were estimated to be in the 30–55 km range;
too small to be seen by ground telescopes, at distances from the Sun
of 43–44 AU, which would put the encounters in the 2018–2019
period. The initial estimated probabilities that these objects
were reachable within New Horizons' fuel budget were 100%, 7%, and
97%, respectively. All were members of the "cold"
(low-inclination, low-eccentricity) classical Kuiper belt, and thus
very different from Pluto. PT1 (given the temporary designation
"1110113Y" on the HST web site), the most favorably situated
object, was magnitude 26.8, 30–45 km in diameter, and will be
encountered around January 2019. Once sufficient orbital
information was provided, the
Minor Planet Center gave official
designations to the three target KBOs:
2014 MU69 (PT1), 2014 OS393
2014 PN70 (PT3). By the fall of 2014, a possible fourth
target, 2014 MT69, had been eliminated by follow-up observations. PT2
was out of the running before the
On August 26, 2015, the first target, 2014 MU69, was chosen. Course
adjustment took place in late October and early November 2015, leading
to a flyby in January 2019. On July 1, 2016,
additional funding for
New Horizons to visit the object.
On December 2, 2015,
New Horizons detected
1994 JR1 from
270 million kilometres (170×10^6 mi) away, and the
photographs show the shape of the object and one or two details.
Extrasolar Kuiper belts
Main article: Debris disc
Debris discs around the stars
HD 139664 and
HD 53143 – black circle
from camera hides star to display discs.
By 2006, astronomers had resolved dust discs thought to be Kuiper
belt-like structures around nine stars other than the Sun. They appear
to fall into two categories: wide belts, with radii of over 50 AU, and
narrow belts (tentatively like that of the Solar System) with radii of
between 20 and 30 AU and relatively sharp boundaries. Beyond
this, 15–20% of solar-type stars have an observed infrared excess
that is suggestive of massive Kuiper-belt-like structures. Most
known debris discs around other stars are fairly young, but the two
images on the right, taken by the
Hubble Space Telescope
Hubble Space Telescope in January
2006, are old enough (roughly 300 million years) to have settled into
stable configurations. The left image is a "top view" of a wide belt,
and the right image is an "edge view" of a narrow belt.
Computer simulations of dust in the
Kuiper belt suggest that when it
was younger, it may have resembled the narrow rings seen around
Book: Solar System
List of possible dwarf planets
List of trans-Neptunian objects
Solar System portal
^ a b The literature is inconsistent in the usage of the terms
scattered disc and Kuiper belt. For some, they are distinct
populations; for others, the scattered disc is part of the Kuiper
belt. Authors may even switch between these two uses in one
publication. Because the International Astronomical Union's Minor
Planet Center, the body responsible for cataloguing minor planets in
the Solar System, makes the distinction, the editorial choice for
articles on the trans-Neptunian region is to make this
distinction as well. On, Eris, the most-massive known
trans-Neptunian object, is not part of the
Kuiper belt and this makes
Pluto the most-massive
Kuiper belt object.
Kuiper belt – oxforddictionaries.com
^ Stern, Alan; Colwell, Joshua E. (1997). "Collisional Erosion in the
Primordial Edgeworth-Kuiper Belt and the Generation of the 30–50 AU
Kuiper Gap". The Astrophysical Journal. 490 (2): 879–82.
^ a b c d e f g Delsanti, Audrey & Jewitt, David. "The Solar
System Beyond The Planets" (PDF). Institute for Astronomy, University
of Hawaii. Archived from the original (PDF) on September 25, 2007.
Retrieved March 9, 2007.
^ Krasinsky, G. A.; Pitjeva, E. V.; Vasilyev, M. V.; Yagudina, E. I.
(July 2002). "Hidden
Mass in the
Asteroid Belt". Icarus. 158 (1):
^ Johnson, Torrence V.; and Lunine, Jonathan I.; Saturn's moon Phoebe
as a captured body from the outer Solar System, Nature, Vol. 435, pp.
^ Craig B. Agnor & Douglas P. Hamilton (2006). "Neptune's capture
of its moon Triton in a binary-planet gravitational encounter" (PDF).
Nature. Archived from the original (PDF) on June 21, 2007. Retrieved
June 20, 2006.
^ a b c Jewitt, David; Luu, Jane (1993). "Discovery of the candidate
Kuiper belt object 1992 QB1". Nature. 362 (6422): 730–732.
^ NEW HORIZONS The PI's Perspective Archived November 13, 2014, at the
^ a b c d Levison, Harold F.; Donnes, Luke (2007). "
and Cometary Dynamics". In Lucy Ann Adams McFadden; Paul Robert
Weissman; Torrence V. Johnson. Encyclopedia of the
Solar System (2nd
ed.). Amsterdam; Boston: Academic Press. pp. 575–588.
^ Weissman and Johnson, 2007, Encyclopedia of the solar system,
footnote p. 584
Minor Planet Center (January 3, 2011). "List Of Centaurs and
Scattered-Disk Objects". Central Bureau for Astronomical Telegrams,
Harvard-Smithsonian Center for Astrophysics. Retrieved January 3,
^ Gérard FAURE (2004). "Description of the System of Asteroids as of
May 20, 2004". Archived from the original on May 29, 2007. Retrieved
June 1, 2007.
^ Randall 2015, p. 106.
^ "What is improper about the term "Kuiper belt"? (or, Why name a
thing after a man who didn't believe its existence?)". International
Comet Quarterly. Retrieved October 24, 2010.
^ Davies, John K.; McFarland, J.; Bailey, Mark E.; Marsden, Brian G.;
Ip, W. I. (2008). "The Early Development of Ideas Concerning the
Transneptunian Region". In M. Antonietta Baracci; Hermann Boenhardt;
Dale Cruikchank; Alessandro Morbidelli. The
Solar System Beyond
Neptune (PDF). University of Arizona Press. pp. 11–23.
^ Davies, John K. (2001). Beyond Pluto: Exploring the outer limits of
the solar system. Cambridge University Press. xii.
^ Davies, p. 2
^ a b David Jewitt. "WHY "KUIPER" BELT?". University of Hawaii.
Retrieved June 14, 2007.
^ a b Davies, p. 14
^ Rao, M. M. (1964). "Decomposition of Vector Measures" (PDF).
Proceedings of the National Academy of Sciences. 51 (5): 771–774.
^ CT Kowal; W Liller; BG Marsden (1977). "The discovery and orbit of
/2060/ Chiron". In: Dynamics of the solar system; Proceedings of the
Symposium. Hale Observatories, Harvard–Smithsonian Center for
Astrophysics. 81: 245. Bibcode:1979IAUS...81..245K.
^ JV Scotti; DL Rabinowitz; CS Shoemaker; EM Shoemaker; DH Levy; TM
King; EF Helin; J Alu; K Lawrence; RH McNaught; L Frederick; D Tholen;
BEA Mueller (1992). "1992 AD".
IAU Circ. 5434: 1.
^ Horner, J.; Evans, N. W.; Bailey, Mark E. (2004). "Simulations of
the Population of Centaurs I: The Bulk Statistics". MNRAS. 354 (3):
798–810. arXiv:astro-ph/0407400 . Bibcode:2004MNRAS.354..798H.
^ Davies p. 38
David Jewitt (2002). "From Kuiper Belt Object to Cometary Nucleus:
The Missing Ultrared Matter". The Astronomical Journal. 123 (2):
1039–1049. Bibcode:2002AJ....123.1039J. doi:10.1086/338692.
^ Oort, J. H. (1950). "The structure of the cloud of comets
Solar System and a hypothesis concerning its origin".
Bull. Astron. Inst. Neth. 11: 91. Bibcode:1950BAN....11...91O.
^ Randall 2015, p. 105.
^ Davies p. 39
^ JA Fernández (1980). "On the existence of a comet belt beyond
Neptune". Monthly Notices of the Royal Astronomical Society. 192:
^ M. Duncan; T. Quinn & S. Tremaine (1988). "The origin of
short-period comets". Astrophysical Journal. 328: L69.
^ Davies p. 191
^ a b Davies p. 50
^ Davies p. 51
^ Davies pp. 52, 54, 56
^ Davies pp. 57, 62
^ Davies p. 65
^ BS Marsden; Jewitt, D.; Marsden, B. G. (1993). "1993 FW".
Planet Center. 5730: 1. Bibcode:1993IAUC.5730....1L.
^ Davies p. 199
^ Clyde Tombaugh, "The Last Word", Letters to the Editor, Sky &
Telescope, December 1994, p. 8
^ M. C. De Sanctis; M. T. Capria & A. Coradini (2001). "Thermal
Evolution and Differentiation of Edgeworth-Kuiper Belt Objects". The
Astronomical Journal. 121 (5): 2792–2799.
^ "Discovering the Edge of the Solar System". American Scientists.org.
2003. Archived from the original on March 15, 2009. Retrieved June 23,
^ Michael E. Brown; Margaret Pan (2004). "The Plane of the Kuiper
Belt". The Astronomical Journal. 127 (4): 2418–2423.
^ Petit, Jean-Marc; Morbidelli, Alessandro; Valsecchi, Giovanni B.
(1998). "Large Scattered Planetesimals and the Excitation of the Small
Body Belts" (PDF). Retrieved June 23, 2007.
^ Lunine, J. (2003). "The Kuiper Belt" (PDF). Retrieved June 23,
^ Jewitt, D. (February 2000). "Classical Kuiper Belt Objects (CKBOs)".
Archived from the original on June 9, 2007. Retrieved June 23,
^ Murdin, P. (2000). "Cubewano". The Encyclopedia of
doi:10.1888/0333750888/5403. ISBN 0-333-75088-8.
^ Elliot, J. L.; et al. (2005). "The Deep Ecliptic Survey: A Search
for Kuiper Belt Objects and Centaurs. II. Dynamical Classification,
the Kuiper Belt Plane, and the Core Population" (PDF). The
Astronomical Journal. 129: 1117–1162. Bibcode:2005AJ....129.1117E.
^ a b "Naming of Astronomical Objects: Minor Planets". International
Astronomical Union. Retrieved November 17, 2008.
^ Petit, J.-M.; Gladman, B.; Kavelaars, J. J.; Jones, R. L.; Parker,
J. (2011). "Reality and origin of the Kernel of the classical Kuiper
Belt" (PDF). EPSC-DPS Joint Meeting (October 2–7, 2011).
^ Levison, Harold F.; Morbidelli, Alessandro (2003). "The formation of
Kuiper belt by the outward transport of bodies during Neptune's
migration". Nature. 426 (6965): 419–421.
^ Stephens, Denise C.; Noll, Kieth S. (2006). "Detection of Six
Trans-Neptunian Binaries with NICMOS: A High Fraction of Binaries in
the Cold Classical Disk". The Astronomical Journal. 130 (2):
1142–1148. arXiv:astro-ph/0510130 . Bibcode:2006AJ....131.1142S.
^ a b Fraser, Wesley C.; Brown, Michael E.; Morbidelli, Alessandro;
Parker, Alex; Batygin, Konstantin (2014). "The Absolute Magnitude
Distribution of Kuiper Belt Objects". The Astrophysical Journal. 782
(2): 100. arXiv:1401.2157 . Bibcode:2014ApJ...782..100F.
^ Levison, Harold F.; Stern, S. Alan (2001). "On the Size Dependence
of the Inclination Distribution of the Main Kuiper Belt". The
Astronomical Journal. 121 (3): 1730–1735. arXiv:astro-ph/0011325 .
^ a b Morbidelli, Alessandro (2005). "Origin and Dynamical Evolution
of Comets and their Reservoirs". arXiv:astro-ph/0512256
^ a b Parker, Alex H.; Kavelaars, J. J.; Petit, Jean-Marc; Jones,
Lynne; Gladman, Brett; Parker, Joel (2011). "Characterization of Seven
Ultra-wide Trans-Neptunian Binaries". The Astrophysical Journal. 743
(1): 1. arXiv:1108.2505 . Bibcode:2011AJ....141..159N.
^ a b c d Levison, Harold F.; Morbidelli, Alessandro; Van Laerhoven,
Christa; Gomes, R. (2008). "Origin of the structure of the Kuiper belt
during a dynamical instability in the orbits of
Uranus and Neptune".
Icarus. 196 (1): 258–273. arXiv:0712.0553 .
^ "List Of Transneptunian Objects". Minor
Planet Center. Retrieved
June 23, 2007.
^ a b Chiang; et al. (2003). "Resonance Occupation in the Kuiper Belt:
Case Examples of the 5:2 and Trojan Resonances". The Astronomical
Journal. 126 (1): 430–443. arXiv:astro-ph/0301458 .
^ Wm. Robert Johnston (2007). "Trans-Neptunian Objects". Retrieved
June 23, 2007.
^ Davies p. 104
^ Davies p. 107
^ E. I. Chiang & M. E. Brown (1999). "Keck Pencil-Beam Survey For
Faint Kuiper Belt Objects" (PDF). Retrieved July 1, 2007.
^ a b c d Bernstein, G. M.; Trilling, D. E.; Allen, R. L.; Brown, K.
E.; Holman, M.; Malhotra, R. (2004). "The size distribution of
transneptunian bodies". The Astronomical Journal. 128 (3):
1364–1390. arXiv:astro-ph/0308467 . Bibcode:2004AJ....128.1364B.
^ Michael Brooks (2007). "13 Things that do not make sense".
NewScientistSpace.com. Retrieved June 23, 2007.
^ Govert Schilling (2008). "The mystery of
Planet X". New Scientist.
Retrieved February 8, 2008.
Pluto may have ammonia-fueled ice volcanoes".
November 9, 2015. Archived from the original on March 4, 2016.
^ Cuzzi, Jeffrey N.; Hogan, Robert C.; Bottke, William F. (2010).
"Towards initial mass functions for asteroids and Kuiper Belt
Objects". Icarus. 208 (2): 518–538. arXiv:1004.0270 .
^ Johansen, A.; Jacquet, E.; Cuzzi, J. N.; Morbidelli, A.; Gounelle,
M. (2015). "New Paradigms For
Asteroid Formation". In Michel, P.;
DeMeo, F.; Bottke, W. Asteroids IV. Space Science Series. University
of Arizona Press. p. 471. arXiv:1505.02941 .
^ Nesvorný, David; Youdin, Andrew N.; Richardson, Derek C. (2010).
"Formation of Kuiper Belt Binaries by Gravitational Collapse". The
Astronomical Journal. 140 (3): 785–793. arXiv:1007.1465 .
^ Hansen, K. (June 7, 2005). "Orbital shuffle for early solar system".
Geotimes. Retrieved August 26, 2007.
^ Tsiganis, K.; Gomes, R.; Morbidelli, Alessandro; Levison, Harold F.
(2005). "Origin of the orbital architecture of the giant planets of
the Solar System". Nature. 435 (7041): 459–461.
^ Thommes, E. W.; Duncan, M. J.; Levison, Harold F. (2002). "The
Jupiter and Saturn". The
Astronomical Journal. 123 (5): 2862–2883. arXiv:astro-ph/0111290 .
^ Parker, Alex H.; Kavelaars, J. J. (2010). "Destruction of Binary
Minor Planets During
Neptune Scattering". The Astrophysical Journal
Letters. 722 (2): L204–L208. arXiv:1009.3495 .
^ Lovett, R. (2010). "Kuiper Belt may be born of collisions". Nature.
^ a b Nesvorný, David; Morbidelli, Alessandro (2012). "Statistical
Study of the Early Solar System's Instability with Four, Five, and Six
Giant Planets". The Astronomical Journal. 144 (4): 117.
arXiv:1208.2957 . Bibcode:2012AJ....144..117N.
^ Nesvorný, David (2015). "Evidence for Slow Migration of Neptune
from the Inclination Distribution of Kuiper Belt Objects". The
Astronomical Journal. 150 (3): 73. arXiv:1504.06021 .
^ Nesvorný, David (2015). "Jumping
Neptune Can Explain the Kuiper
Belt Kernel". The Astronomical Journal. 150 (3): 68.
arXiv:1506.06019 . Bibcode:2015AJ....150...68N.
^ Fraser, Wesley; and 21 others (2017). "All planetesimals born near
Kuiper belt formed as binaries". Nature Astronomy. 1: 0088.
arXiv:1705.00683 . Bibcode:2017NatAs...1E..88F.
^ Wolff, Schuyler; Dawson, Rebekah I.; Murray-Clay, Ruth A. (2012).
Neptune on Tiptoes: Dynamical Histories that Preserve the Cold
Classical Kuiper Belt". The Astrophysical Journal. 746 (2): 171.
arXiv:1112.1954 . Bibcode:2012ApJ...746..171W.
^ Morbidelli, A.; Gaspar, H. S.; Nesvorny, D. (2014). "Origin of the
peculiar eccentricity distribution of the inner cold Kuiper belt".
Icarus. 232: 81–87. arXiv:1312.7536 . Bibcode:2014Icar..232...81M.
^ a b c d e f Brown, Michael E. (2012). "The Compositions of Kuiper
Belt Objects". Annual Review of
Earth and Planetary Sciences. 40 (1):
467–494. arXiv:1112.2764 . Bibcode:2012AREPS..40..467B.
^ a b c David C. Jewitt &
Jane Luu (2004). "Crystalline water ice
Kuiper belt object (50000) Quaoar" (PDF). Archived from the
original (PDF) on June 21, 2007. Retrieved June 21, 2007.
^ a b Dave Jewitt (2004). "Surfaces of Kuiper Belt Objects".
University of Hawaii. Archived from the original on June 9, 2007.
Retrieved June 21, 2007.
^ a b Jewitt, David; Luu, Jane (1998). "Optical-
Diversity in the Kuiper Belt". The Astronomical Journal. 115 (4):
1667–1670. Bibcode:1998AJ....115.1667J. doi:10.1086/300299.
^ Davies p. 118
^ Jewitt, David C.; Luu, Jane X. (2001). "Colors and Spectra of Kuiper
Belt Objects". The Astronomical Journal. 122 (4): 2099–2114.
arXiv:astro-ph/0107277 . Bibcode:2001AJ....122.2099J.
^ Brown, R. H.; Cruikshank, DP; Pendleton, Y; Veeder, GJ (1997).
"Surface Composition of Kuiper Belt Object 1993SC". Science. 276
(5314): 937–9. Bibcode:1997Sci...276..937B.
doi:10.1126/science.276.5314.937. PMID 9163038.
^ Wong, Ian; Brown, Michael E. (2017). "The bimodal color distribution
of small Kuiper Belt objects". The Astronomical Journal. 153 (4): 145.
arXiv:1702.02615 . Bibcode:2017AJ....153..145W.
^ Brown, Michael E.; Blake, Geoffrey A.; Kessler, Jacqueline E.
Spectroscopy of the Bright Kuiper Belt Object
2000 EB173". The Astrophysical Journal. 543 (2): L163.
^ Licandro; Oliva; Di MArtino (2001). "NICS-TNG infrared spectroscopy
of trans-neptunian objects 2000 EB173 and 2000 WR106".
Astrophysics. 373 (3): L29. arXiv:astro-ph/0105434 .
^ Gladman, Brett; et al. (August 2001). "The structure of the Kuiper
belt". Astronomical Journal. 122 (2): 1051–1066.
^ Nesvorný, David; Vokrouhlický, David; Bottke, William F.; Noll,
Keith; Levison, Harold F. (2011). "Observed Binary Fraction Sets
Limits on the Extent of Collisional Grinding in the Kuiper Belt". The
Astronomical Journal. 141 (5): 159. arXiv:1102.5706 .
^ Shankman, C.; Kavelaars, J. J.; Gladman, B. J.; Alexandersen, M.;
Kaib, N.; Petit, J.-M.; Bannister, M. T.; Chen, Y.-T.; Gwyn, S.;
Jakubik, M.; Volk, K. (2016). "OSSOS. II. A Sharp Transition in the
Absolute Magnitude Distribution of the Kuiper Belt's Scattering
Population". The Astronomical Journal. 150 (2): 31.
arXiv:1511.02896 . Bibcode:2016AJ....151...31S.
^ Alexandersen, Mike; Gladman, Brett; Kavelaars, J.J.; Petit,
Jean-Marc; Gwyn, Stephen; Shankman, Cork (2014). "A carefully
characterised and tracked Trans-Neptunian survey, the
size-distribution of the Plutinos and the number of Neptunian
Trojans": (page needed). arXiv:1411.7953 [astro-ph.EP].
^ "Hubble Finds Smallest Kuiper Belt Object Ever Seen". HubbleSite.
December 2009. Retrieved June 29, 2015.
^ a b c "List Of Centaurs and Scattered-Disk Objects". IAU: Minor
Planet Center. Retrieved October 27, 2010.
David Jewitt (2005). "The 1000 km Scale KBOs". University of Hawaii.
Retrieved July 16, 2006.
^ Craig B. Agnor & Douglas P. Hamilton (2006). "Neptune's capture
of its moon Triton in a binary-planet gravitational encounter" (PDF).
Nature. Archived from the original (PDF) on June 21, 2007. Retrieved
October 29, 2007.
^ Encrenaz, Thérèse; Kallenbach, R.; Owen, T.; Sotin, C. (2004).
TRITON, PLUTO, CENTAURS, AND TRANS-NEPTUNIAN BODIES.
Research Center. Springer. ISBN 978-1-4020-3362-9. Retrieved June
^ Mike Brown (2007). "Dysnomia, the moon of Eris". Caltech. Retrieved
June 14, 2007.
^ "Resolution B5 and B6" (PDF). International Astronomical Union.
^ "Ixion". eightplanets.net. Archived from the original on October 3,
2012. Retrieved June 23, 2007.
^ John Stansberry; Will Grundy; Mike Brown; Dale Cruikshank; John
Spencer; David Trilling; Jean-Luc Margot (2007). "Physical Properties
of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space
Telescope". arXiv:astro-ph/0702538 .
IAU Draft Definition of Planet". IAU. 2006. Archived from the
original on October 5, 2011. Retrieved October 26, 2007.
^ Brown, M. E.; Van Dam, M. A.; Bouchez, A. H.; Le Mignant, D.;
Campbell, R. D.; Chin, J. C. Y.; Conrad, A.; Hartman, S. K.;
Johansson, E. M.; Lafon, R. E.; Rabinowitz, D. L. Rabinowitz; Stomski,
P. J., Jr.; Summers, D. M.; Trujillo, C. A.; Wizinowich, P. L. (2006).
"Satellites of the Largest Kuiper Belt Objects" (PDF). The
Astrophysical Journal. 639 (1): L43–L46. arXiv:astro-ph/0510029 .
Bibcode:2006ApJ...639L..43B. doi:10.1086/501524. Retrieved October 19,
^ Agnor, C.B.; Hamilton, D.P. (2006). "Neptune's capture of its moon
Triton in a binary-planet gravitational encounter" (PDF). Nature. 441
(7090): 192–4. Bibcode:2006Natur.441..192A. doi:10.1038/nature04792.
^ a b Brown, Dwayne; Villard, Ray (October 15, 2014). "RELEASE 14-281
NASA's Hubble Telescope Finds Potential Kuiper Belt Targets for New
Pluto Mission". NASA. Retrieved October 16, 2014.
^ "New Frontiers Program:
New Horizons Science Objectives".
NASA - New
Frontiers Program. Archived from the original on April 15, 2015.
Retrieved April 15, 2015.
^ a b c Lakdawalla, Emily (October 15, 2014). "Finally! New Horizons
has a second target".
Planetary Society blog. Planetary Society.
Archived from the original on October 15, 2014. Retrieved October 15,
^ "NASA's Hubble Telescope Finds Potential Kuiper Belt Targets for New
Pluto Mission". press release. Johns Hopkins Applied Physics
Laboratory. October 15, 2014. Archived from the original on October
16, 2014. Retrieved October 16, 2014.
^ Wall, Mike (October 15, 2014). "Hubble Telescope Spots Post-Pluto
New Horizons Probe". Space.com. Archived from the original
on October 15, 2014. Retrieved October 15, 2014.
^ Buie, Marc (October 15, 2014). "
New Horizons HST KBO Search Results:
Status Report" (PDF). Space Telescope Science Institute.
^ "Hubble to Proceed with Full Search for
New Horizons Targets".
HubbleSite news release. Space Telescope Science Institute. July 1,
2014. Retrieved October 15, 2014.
^ Stromberg, Joseph (April 14, 2015). "NASA's
New Horizons probe was
Pluto — and just sent back its first color photos". Vox.
Retrieved April 14, 2015.
^ Corey S. Powell (March 29, 2015). "Alan Stern on Pluto's Wonders,
New Horizons' Lost Twin, and That Whole "Dwarf Planet" Thing".
^ "Orbits and Accessibility of Potential
New Horizons KBO Encounter
Targets" (PDF). USRA-Houston. 2015. Archived from the original (PDF)
on March 3, 2016.
^ McKinnon, Mika (August 28, 2015). "
New Horizons Locks Onto Next
Target: Let's Explore the Kuiper Belt!". Archived from the original on
December 31, 2015.
^ Dwayne Brown / Laurie Cantillo (July 1, 2016). "New Horizons
Receives Mission Extension to Kuiper Belt, Dawn to Remain at Ceres".
NASA. Retrieved May 15, 2017.
^ New Horizons' catches a wandering Kuiper Belt Object not far off
spacedaily.com Laurel MD (SPX). December 7, 2015.
^ a b Kalas, Paul; Graham, James R.; Clampin, Mark C.; Fitzgerald,
Michael P. (2006). "First Scattered Light Images of Debris Disks
HD 53143 and HD 139664". The Astrophysical Journal. 637: L57.
arXiv:astro-ph/0601488 . Bibcode:2006ApJ...637L..57K.
^ Trilling, D. E.; Bryden, G.; Beichman, C. A.; Rieke, G. H.; Su, K.
Y. L.; Stansberry, J. A.; Blaylock, M.; Stapelfeldt, K. R.; Beeman, J.
W.; Haller, E. E. (February 2008). "Debris Disks around Sun-like
Stars". The Astrophysical Journal. 674 (2): 1086–1105.
arXiv:0710.5498 . Bibcode:2008ApJ...674.1086T.
^ "Dusty Planetary Disks Around Two Nearby Stars Resemble Our Kuiper
Belt". 2006. Retrieved July 1, 2007.
^ Kuchner, M. J.; Stark, C. C. (2010). "Collisional Grooming Models of
the Kuiper Belt Dust Cloud". The Astronomical Journal. 140 (4):
1007–1019. arXiv:1008.0904 . Bibcode:2010AJ....140.1007K.
Randall, Lisa (2015). Dark Matter and the Dinosaurs. New York:
Ecco/HarperCollins Publishers. ISBN 978-0-06-232847-2.
Wikimedia Commons has media related to Kuiper belt.
Dave Jewitt's page @ UCLA
The belt's name
List of short period comets by family
Kuiper Belt Profile by NASA's
Solar System Exploration
The Kuiper Belt Electronic Newsletter
Wm. Robert Johnston's TNO page
Planet Center: Plot of the Outer Solar System, illustrating
Website of the
International Astronomical Union
International Astronomical Union (debating the status
XXVIth General Assembly 2006
nature.com article: diagram displaying inner solar system, Kuiper
Belt, and Oort Cloud, taken from Alan Stern, S. (2003). "The evolution
of comets in the
Oort cloud and Kuiper belt". Nature. 424 (6949):
639–42. doi:10.1038/nature01725. PMID 12904784.
SPACE.com: Discovery Hints at a Quadrillion Space Rocks Beyond Neptune
(Sara Goudarzi) August 15, 2006 06:13 am ET
Astronomy Cast episode No. 64, includes
Kuiper belt at 365daysofastronomy.org
Nine Planets' webpage on the Edgeworth-Kuiper Belt and Oort Cloud
List of TNOS
Solar System bodies
Meanings of names
Distant minor planet
No longer rounded and therefore not dwarf planets (Former candidates:
1995 SN55 (lost)
Additional objects proposed by Brown and Tancredi: Orcus
Possibly: 2003 UZ413
Possibly: 2002 WC19
Possibly: 2002 XW93
Additional objects proposed by Brown and Tancredi: 2002 MS4
Additional objects proposed by Brown and Tancredi: 2007 OR10
Possibly: 2002 TC302
Captured satellites that were once dwarf planets: Triton (captured by
Phoebe (captured by Saturn, and no longer rounded)
2011 FW62 (lost)
Possibly: 2004 XR190
Objects proposed by Brown and Tancredi: Sedna
Possibly: 2012 VP113
See also: Charon
List of trans-Neptunian objects
List of possible dwarf planets
Solar System objects
Solar System objects by size
The Solar System
S/2015 (136472) 1
Solar System objects
By discovery date
Gravitationally rounded objects
Possible dwarf planets
first discovered: Ceres
Planets beyond Neptune
List of crewed spacecraft
List of probes
Outline of the Solar System
Solar System → Local Interstellar Cloud → Local
Bubble → Gould Belt → Orion Arm → Milky
Milky Way subgroup → Local Group → Virgo
Supercluster → Laniakea Supercluster → Observable
universe → Universe
Each arrow (→) may be read as "within" or "part of".