Kuiper Belt:

Project No.039

teacher Ionita Iulian

Banc Florian-Mihai

Ionita Alexandru-Lucian

Tudor Andrei-Mihai


     Scoala Nr.82

Motto:   "Space-the final frontier".

The Kuiper Belt

I. Introduction

     Long time after Pluto was discovered (1930) people believed that it is the final frontier of our Solar System.
     The Dutch astronomer, Gerald Kuiper (1905-1973) put forward a new theory of how the solar system was formed (the nebula theory of dust and gas), and it is generally accepted today. The old theory it was that the planets had formed from material hurled from the Sun. Kuiper argued that a gas and dust cloud collapsed under gravity, forming the Sun and planets separately.

Img. 1
Cloud of dust and gas

Img. 2
Proto sun and protoplanets

Img. 3
Sun and planets
     In 1951 Kuiper suggest that short-period comets coming   just beyond Pluto and the asteroids - leftover material from the solar system - between Mars and Jupiter are not all that remains from the forming of solar system. Kuiper's hypothesis was reinforced in the early 1980s when computer simulations of the solar system's formation predicted that a disk of debris should naturally form around the edge of the solar system. According to this scenario, planets would have agglomerated quickly in the inner region of the Sun's primordial circumstellar disk, and gravitationally swept up residual debris. However, beyond Neptune, the last of the gas giants, there should be a debris-field of icy objects that never coalesced to form planets. >From 1992 onwards, astronomers began to discover large numbers of these bodies.
     When the first body (KBOs) were discovered the belt was named in his honour.

     The Kuiper Belt it is important for:
  1. the study of the planetary system, because it is widely believed that the Kuiper Belt objects (KBOs) are remains from the forming of the solar system. The inner, dense part of the pre-planetary disk condensed into the major planets, probably within a few millions to tens of millions of years. The outer parts were less dense, and accretion progressed slowly. Evidently, a great many small objects were formed;
  2. to keep watch for comets, because it is suspected that the Kuiper Belt is the source of the short-period comets (period < 200 years) as the Oort Cloud is the source of the long-period comets (period >200 years).

II. Main features of Kuiper Belt

      The Kuiper Belt is a long-lived region of the solar system which consist of a vast population of small bodies orbiting in a radial zone extending outwards from 30AU (the orbit of Neptune) to 50AU (1 AU is an "Astronomical Unit" and is equal to the distance between the Earth and the Sun, about 150 million kilometres). It is made up of as many as 100,000 objects 100km in diameter or larger and also of huge numbers of smaller members. The KB demarcates the transition from the giant planets made up of rock, ice and gas to the smaller bodies, which are made of just rock and ice.
      Observations show that the Kuiper Belt objects are mostly confined within a thick band around the ecliptic, leading to the realization that they occupy a ring or belt surrounding the sun.

Img. 4
Img. 5

    These bodies exist in three dynamical classes:

  1. the Classical KBOs occupy nearly circular (eccentricities e < 0.25) orbits with semimajor axes
    41 AU < a < 46 AU, and they constitute ~70% of the observed population;
  2. the Resonant KBOs (Plutinos) occupy
    mean-motion resonances with Neptune, such as the 3:2 (a=39.4 AU) and 2:1
    (a=47.8 AU). This means that they complete 2 orbits around the sun in the time it takes Neptune to complete 3 orbits or they complete 1 orbit around the sun in the time it takes Neptune to complete 2. Represent ~20% of the known objects;
  3. the Scattered KBOs represent only ~10% of the known KBOs, but possess the most extreme orbits, with median semimajor axis a ~90 AU and eccentricity (a measure of the ellipticity of a circle) e ~0.6, presumably due to a weak interaction with Neptune.

Img. 6    The symbols in the Figure have the following meanings:
J=Jupiter, N=Neptune
Red Orbits = Plutinos. Blue Orbits = Classical Kuiper Belt Objects. Black Orbits = SKBOs.

Some of KBOs are binaries.

Img. 7

Img. 8
From July to September 2001, December 2001, and January to February 2002 NASA's Hubble Space Telescope took pictures of a double system of icy bodies, called 1998 WW31, in the Kuiper Belt. The blue oval represents the orbital path.

Pluto has been known to be binary since 1978. From total of about 800 KBOs witch are know after 2002, 8 are binaries.


Semi majoraxis



Orbital period


19 600




1998 WW31

22 300




2001 QT297





2001 QW322





1999 TC36





1998 SM165





1997 CQ29





2000 CF105





2001 QC289






For the Kuiper Belt binaries formation is some ideas but neither of them is generally accepted.

Kuiper Belt binaries might have formed:
  1. by collisions between KBOs. When the relative velocities are smaller than or comparable to the gravitational escape speeds from the colliding objects, some fraction of the collisions will "stick"; resulting in peanut shaped contact binaries. Others will bounce, with some ejection of mass (and energy) allowing binaries to form. Still others will collide but not lose enough energy in order to become bound. In this scenario, the binary KBOs are products of low velocity (100 m/s) collisions in the Kuiper Belt.
    But collisions between 100 km sized KBOs are currently very rare;
  2. by dynamical friction. Three-body interactions have also been proposed, in which two objects become more tightly bound when a third carries away some of their kinetic energy. A hybrid mechanism, in which collisions create a unique binary and then the small component is ejected on the close pass of a third, has also been advanced. The different suggestions make distinct predictions about the ratio of wide to narrow binaries and thus offer a future observational test.
    But Kuiper Belt is less denser so that these idea to be effective.

    The astronomers suspect that most Kuiper Belt Objects are made of equal portions of rock and ices with some organic (carbon-containing) material such as tholin. Tholin is a heteropolymer formed by solar ultraviolet irradiation of simple organic compounds such as methane or ethane. Tholins do not form naturally on modern-day Earth, but are found in great abundance on the surface of icy bodies in the outer solar system.

III. Largest Discoveries

    The Kuiper belt remained theory until the 1992 detection of a 150-mile wide body, called 1992QB1 at the distance of the suspected belt.

Img. 9
Click to enlarge
The historical picture of the 1992 QB1 discover, made by D. Jewitt and J. Luu.
Its semimajor axis is 41.197 AU and the red colour suggests a surface composition rich in organics.

     Several similar-sized objects were discovered quickly confirming the Kuiper Belt was real. The planet Pluto, discovered in 1930, is considered the largest member of this Kuiper Belt region. Also, Neptune's satellites, Triton and Nereid, are in unusual orbits and may be captured Kuiper Belt objects.
The range of the sizes of KBOs is very large. Little by little the number of the members of 1000 km diameter objects are increasing filling the gap from Pluto to more commonly measured objects.

     The table below shows the largest KBOs has been discovered until 2004.


Equatorial diameter

Mean distance from the sun


Date discovered































2002 TX300





2002 UX25





2002 AW197





Img. 10


  Img. 11

     Quaoar is the name of the creation god of the Tongva native American tribe, the original inhabitants of the Los Angeles basin. According to legend, Quaoar "came down from heaven; and, after reducing chaos to order, laid out the world on the back of seven giants. He then created the lower animals, and then mankind."
     Quaoar complete a circle around the sun in 285 Earth years.
    The orbit of Quaoar is nearly circular. Its eccentricity is less than 0.04, meaning that its distance from the sun only changes by about 8% over the course of a Quaoar year. Quaoar's orbit is also inclined to the ecliptic (the plane of the solar system), by about 8 degrees.
You can see its orbit below

Img. 12

     Quaoar is very bright because on it are different types of ice: water ice, methanol ice, methane ice, carbon monoxide ice, carbon dioxide ice and others.


    Orcus is one of the largest Kuiper Belt objects currently known. It was discovered on 17 February 2004.
    Name Orcus comes from the god of the dead in Roman mythology and same time from another name for the Greek deity, Hades.
     It is a "Plutino" because it goes around the sun twice for every 3 times that Neptune goes around the sun, same to Pluto.

Img. 13   The known planets are in black, Orcus is in red and Pluto in green.


Orbital period 247.94 Earth years.

Mean orbital speed 4.68 km/s

Eccentricity 0.218

Inclination 20.559 o

Mean Surface Temperature ~61 K
It is suspected that its components are same Quaoar's: rocks, water ice, methanol ice, methane ice, carbon monoxide ice, carbon dioxide ice and others.

IV. How did the scientists obtain the information - which observations did they perform? How sure are they about what they say about the object?

    Finding an astronomical body past Neptune, is like trying to see a 100-watt light bulb at 20 times the distance of the Moon! For that reason the scientists try to found different ways to discover new objects and measure theirs qualities.
    Some of these are:

- physical and mathematical theories;

- computer simulations;

- optical measurements;

- thermal measurements;

- spectroscopy detections;

- infrared detections;

- radio astronomy.

    At the same time by the development of technology was increased the number of discovered KBOs. Clyde Tombaugh found Pluto in 1930 using photographic plates, which did not have a good resolution and for that Charon (Pluto's moon) were discovered in 1978. Today, CCD's are getting large enough and computers are getting fast enough that it is significantly easier to find these types of planetoids.
    Orcus and Quaoar had been found with the Oschin Telescope at Palomar, a semi-automated telescope, with a mirror diameter of 1.2 meters and field of view about 3 square degrees. Most professional telescopes have a mirror diameter between 1 and 10 meters.
    Hubble Space Telescope (HST) is one of the best instruments used by scientists for detect and measure KBOs.

Img. 14   The discovery images of Orcus
Img. 15   Here are the discovery images of Quaoar.
Three pictures of the same patch of sky with 90 minutes between them.

    Measurement of the size of a KBO is difficult. The apparent optical brightness, corrected to a standard distance from the sun and Earth, is called the "absolute magnitude"; H. Absolute magnitude provides a measure of the product of the albedo (a measure of reflectivity of a surface or body) of the KBO with the square of its diameter. By taking thermal data as well as optical, it is possible to disentangle the albedo from the squared diameter, and obtain separate values for both. This is because high albedo objects of a given size are optically bright but thermally cold (because they reflect, not absorb, most of the sun's radiation) and therefore thermally faint. Conversely, a low albedo object of the same size would be optically faint, but thermally bright (because the surface absorbs most of the sunlight and becomes warm).

In his web page Chadwick A. Trujillo, the co-discoverer of Quaoar and Orcus, explain:

How do we know how big Quaoar is?
We measured the size of Quaoar in two ways:

(1) Optical measurements using the Hubble Space Telescope. Using a normal ground based telescope, you can't see Quaoar's size directly. You can tell it's there, but it's just a pinpoint of light just like any other star. But, the Hubble Space Telescope (HST) has much better "angular resolution" (it can see details a lot better) than a normal telescope because it is outside the Earth's atmosphere. By very carefully measuring Quaoar's size about 10 times over the course of an hour and comparing them to a nearby star, we can see directly that Quaoar is 1250 km in diameter.

(2) Thermal measurements. Using the IRAM telescope in Spain, we measured the heat coming from Quoar. Optical wavelength light (i.e. what your eye sees and what a "normal" telescope measures) only tells you about the amount of sunlight that is reflected from Quaoar back to Earth. So, a small white object could reflect the same amount of light as a large dark object. However, a dark object absorbs much more light than a white object, so it will be hotter. By measuring the heat (1.2 millimeter wavelength "light") coming from Quaoar and comparing it with the optical reflected light, we know that Quaoar has a diameter of 1250 km.

How big is 2004 DW (Orcus)?

So far, we are not sure. The size has not been accurately measured like the size of Quaoar has. However, we know the object's distance very roughly as well as its brightness. Using this and our best guess at the object's albedo (how light or dark the surface is) of 9%, the object is probably about 1600 km in diameter, larger than the 1250 km Quaoar. If subsequent measurements verify this size estimate, this would make Quaoar the largest minor planet known, and larger than Pluto's moon Charon, which is about 1300 km in diameter. This still doesn't beat Pluto, which is about 2300 km in diameter.

    In 2001 a European scientists team from ESO used the world's first operational "virtual telescope", Astrovirtel, to measure the size of a KBO named Ixion. This method, which mimics a telescope, provides astronomers a high-quality data, which allowed a substantial improvement of the accuracy of the computed orbit for Ixion.

V. The Kuiper Belt and the Oort Cloud

    The Oort Cloud, named after Jan Hendrik Oort, is a postulated spherical cloud of comets situated about 50,000 to 100,000 AU from the Sun. The statistics imply that it may contain as many as a trillion comets. Because the individual comets are so small and at such large distances, the comets from the Oort Cloud haven't seen with the telescopes, but the mathematicians calculated that it has to be the home of the comets that come into the Inner Solar System from any direction. These comets, named long-period comets, take a long time to fall in, and then they take a long time to come back and visit us again. Maybe that Hale-Bopp is one of these comets.
    The American astronomer, Gerard P.Kuiper, in 1951, proposed that the comets which come around in less than 200 years (like Halley's or Shoemaker-Levy) have to come from much closer in. These comets come from the plane of the planets, rather than from any old direction. That mean, based on observations of their orbits, there should be a flattened belt or disc of comets, beginning just outside the orbit of Neptune and extending roughly from 30 to 50 AU from the Sun.
    The most widely-accepted theory of its formation is that the Oort Cloud's objects initially formed much closer to the Sun as part of the same process that formed the planets and asteroids, but that gravitational interaction with young gas giants such as Jupiter ejected them into extremely long elliptical or parabolic orbits. This process also served to scatter the objects out of the ecliptic plane, explaining the cloud's spherical distribution. While on the distant outer regions of these orbits, gravitational interaction with nearby stars further modified their orbits to make them more circular. The small objects formed farther out had no such interactions with young giant planets and remained as the Kuiper Belt objects.
   Img. 16

    In 2004, one potential Oort Cloud object has been discovered; it is know as 2003 VB12 "Sedna". Its orbit is intermediate between the Kuiper Belt and what was previously thought to be the inner part of the Oort Cloud (roughly 76 to 850 AU). Perhaps this object is the first of a new class of "inner Oort Cloud" objects.     

It is thought that other stars are likely to possess Oort clouds of their own.

    Img. 17 Beta Pictoris was found to be an unexpectedly strong source of thermal radiation (from dust) by the IRAS satellite in 1984. Soon after, Smith and Terrile discovered an optical disk around the star. The spectrum of Beta Pic shows red-shifted absorption lines that have been interpreted by some as evidence for comets falling onto the photosphere.

     How appears a long-period comet?

    One theory was that every few million years, a distant passing star would disturb the Oort Cloud with its massive gravity, and so start a few comets on a million-year trip to the inner solar system.

     How appears a short-period comet?

    A recent theory is that the gravitational field of Neptune disturbs the Kuiper Belt, and a comet is pulled towards Neptune, fall into the inner solar system and come under the gravitational control of the planets being tossed towards the Sun. According to this theory, a comet from the Kuiper Belt should hit Jupiter every 400 years, and Earth, every 13 million years or so.

VI. The Experiment:

    We researched into how a distant passing star can disturb the Oort Cloud. For this experiment we used a device with air mass to reduce the friction, ten green magnetic pucks, which represent the asteroids from Oort Cloud and one red magnetic puck that represent the star. The pucks interacted by the magnetic fields as the star and asteroids interact by the gravitational fields. Between green pucks and red puck we put a magnetic barrier to reduce the forces.

The images below show how we performed our experiment:

Img. 18
The device
Img. 19
The experiment
Img. 20

    We observed that the green pucks are moved on random directions under the action of magnetic field of the red puck.
    We think that the passing star produces random movements to a part of asteroids. Some of the comets fall into the inner solar system and come under the gravitational control of the planets. An equal number of comets are ejected from the Oort Cloud to interstellar space.

VII. New Horizons

   Img. 21
    For the scientists the Kuiper Belt it is a very intriguing world. Objects in which it consists are postulated to be composed of the pristine material, which formed our solar system and may even have organic material in them. A detailed study of KBO's size, orbit, distribution, structure and surface composition could disclose a part from the mysteries of the origin of the solar system and perhaps even from the origin of life in our solar system.
KBOs range in colours from grey to red. Pluto's surface is very complex with areas ranging from “darker than coal” to “brighter than snow”. The theory of that diversity of colours is that the frost on the surface of Kuiper Belt Objects gets darker and redder with exposure to energetic particles and photons from the Sun, and grey again if an impact throws up new, clean frost from below the reddened surface.
   Img. 22

    In January 2006 is scheduled to launch a spacecraft, named New Horizons, who will reach Pluto and its moon, Charon, in July 2015 and then will explore one or more Kuiper Belt Objects. To study Pluto, Charon, and KBOs, the New Horizons mission has a payload designed to answer the most important questions about unexplored bodies in the outer solar system. How do they look? What are they made of? What are their atmospheres like? The mission plans to map surface appearance with visible-wavelength cameras; study surface composition by spectra in the near infrared; and probe the atmosphere with ultraviolet spectrometers and radio waves, studying the particles leaving the atmosphere, and the effect of the atmosphere on the solar wind.




VIII. Bibliography


24 May 2001: "Nature"

2004 May: "The Astronomical Journal"

      Web pages:










IX. References for the individual images

Img. 1, 2, 3, 10 - made by Ionita Alexandru Lucian

Img. 4 - www.harmsy.freeuk.com

Img. 5 - John Hopkins University

Img. 6, 7, 9, 17, 22 - www.ifa.hawaii.edu/faculty/jewitt/kb.html

Img.11- www.windows.ucar.edu

Img. 12, 13 - www.gps.caltech.edu%7Echad/quaoar

Img. 14, 15 - www.gps.caltech.edu/~chad/2004dw


Img. 21 - http;//space.com/scienceastronomy/names_game_030812.htm