The Discovery of Pluto, The Kuiper Belt and Understanding the Universe

By: Breanne Gelowitz, Bryn Hawkins, Sara Humphreys, Martina Ratt, and Zach Mirasty

The Kuiper Belt and the bodies orbiting within it, such as Pluto and other “dwarf planets” have been researched but have not been shared with the public as common knowledge to people outside the astronomy field. Our mission much like New Horizons’ mission (
to explore Pluto and the Kuiper Belt) is to demonstrate that the continuous reassessment of existing scientific knowledge is crucial when considering the progression of the universe and how we see it. For example, the discovery of Pluto has led astronomers to research the region of which Pluto belongs to, leading us to our awareness of the Kuiper Belt itself. The importance of studying the Kuiper Belt is being able to investigate all of its objects and to learn more about our universe. When Pluto was discovered in the 1930’s and recalled as a planet in 2006, the discovery of the fulfilled space past Neptune that includes “Dwarf” planets like Pluto, as well as many other identifiable objects, is known as the Kuiper Belt. Our main question that we seek to answer is “What do astronomers know about the Kuiper Belt as well as the objects that belong to it, what methods did they use to discover these objects, and why? ”

Figure 1- Clyde Tombaugh and His Telescope O’Hara, Elva R. (2006). KHWu6CKAQpwUIHw&biw=1280&bih=649&dpr=1#imgrc=61DxUDA9QSJqHM:

Pluto’s Discovery to Pluto Now

The discovery of what is now reclassified as the dwarf planet was founded on February 18th, 1930 by Clyde Tombaugh at the Lowell Observatory. Percival Lowell, began to look at the orbits of Neptune and Uranus and suggested that there was a gravity change past Neptune and predicted this gravity change was “Planet X”. Before he could discover Pluto, he passed away. Lowell’s predictions helped Tombaugh’s and other astronomers research. Tombaugh accepted a job offer with the Lowell Observatory and began searching for Planet X. Around this time period, there was a new astronomic method for interpreting change over a series of nights. The method uses a blink microscope as well as photographic plates. The observatory had a telescope that took two photographs of the sky on separate days to show movement. A blink comparator, a gadget that quickly turns over the photographs repetitively. In the pictures, galaxies of stars would be still but objects that are close could be seen due to its movement throughout the sky. Tombaugh studied the two pictures for weeks and months and finally on February 18th, 1930 he realized something was moving across the field when he examined an image from a month prior. After Lowell Observatory’s staff closely studied Tombaugh’s findings, they broadcasted the ninth planet’s discovery of Planet X, which is now known as Pluto1.

In 2006 however, the 9th planet was “reclassified as a dwarf planet” due to its size. The International Astronomical Union has three principles that determine whether an object is a planet or not. The three criterion are: it orbits the sun, it has enough mass to reach hydrostatic equilibrium or obtain a spherical shape, and it has enough mass to be considered dominant in its surroundings. Pluto qualifies in 2 out of 3 of the categories, but the final category its fails to meet the guideline because it has a similar mass compared to other objects in its vicinity2.
Pluto’s current status is at a crossroads as in 2017 a science group proposed a more recent definition of planethood. The new definition would expand the solar system to around 100
planets 2.

KBO Objects Worth Mentioning

Keeping Pluto company out in the Kuiper belt, are many other objects worthy of mention: Quaoar, Makemake, Haumea, Orcus, and Eris are all large icy bodies in the Belt. Several of them even have moons of their own. These are all tremendously far away, and, yet very much within reach. Each of these large icy bodies is classified as Dwarf Planets.
As discussed before, objects have to meet specific criteria to be classified as a planet, first, “The object must be in direct orbit around the Sun, it must be in hydrostatic equilibrium, and the object must be able to clear the smaller objects out of its orbit”2.
The first condition cannot be misinterpreted, all planets and other objects, such as comets and asteroids, orbit the sun. Pluto is no different, however, its orbital characteristics are peculiar in comparison to other planets. Several reasons for this is that Pluto is found on a different plane than other objects “and is inclined to an angle of 17 degrees”9. It has also been noted that Pluto’s strange elliptical rotation causes it to overlap with Neptune’s Orbit. Pluto’s orbit having an elliptical shape causes it to be closer to the sun at some points and closer to Neptune on other parts of its rotation. The last time that Pluto was “witnessed being closer to the sun than Neptune was from 1979-1999 and will not happen again until 2227”9.
The second requirement for a planet to be in hydrostatic equilibrium, meaning, gravity compression is balanced by pressure being pushed outward. The planet has to be spherical, and the more mass that a planet has equated to more internal pressure and a rounder shape. Michael Moltenbrey in his book Dawn of Small Worlds: Dwarf Planets, Asteroids, Comets, explains how dwarf planets fail to complete the third part of the criteria; they are unable “ to clear their orbital region over time by causing the smaller bodies to collide with another planet, capture it as a satellite, or force it into a resonant orbit”12.


TheKuiperBelt Orbits Pluto Polar.svg

By No machine-readable author provided. Eurocommuter~commonswiki assumed (based on copyright claims). – No machine-readable source provided. Own work assumed (based on copyright claims)., CC BY-SA 3.0, Link

The first dwarf planet, Pluto, was classified in 2006 after the discovery of Eris in 2005 causing the AIU to reconsider what objects could be classified as planets. Since then four other dwarf planets have been discovered or certain KBO’s were re-classified.
Also worthy of mentioning are short-period comets due to their unique properties and behaviors. Short-period comets are those that take less than 200 years to orbit the sun and are found within the Kuiper Belt. Short period comets have “much lower typical inclinations”, meaning they are “within 30 degrees of the solar system plane”. Comets are important to understanding the formation of the solar system and according to NASA, comets may have brought water and organic compounds, the building blocks of life, to the early Earth and other parts of the solar system”2. The most famous short-period comet is Halley.




The Kuiper Belt

n the video below, the presenter Mike Brown explains that “The Kuiper Belt is a collection of bodies outside the orbit of Neptune”4, and if Neptune was not a discovered planet or never assembled, the bodies out past Neptune could have come together to form a new planet. Alternatively, B. Dunford, a scientific writer said that the formation of Neptune made objects unavailable to unite which created a belt of material located beyond Neptune<sup>5</sup>.

Video- What is the Kuiper Belt?

How the Kuiper Belt came to be is interesting. The first suggestion of a possible string of comets and large celestial bodies that were beyond the bounds of the planets was in 1943 by astronomer Kenneth Edgeworth. He stated that there was a “reservoir of comets beyond the planets”5. After hearing about this phenomenon, Astronomer Gerard Kuiper spent a chunk of time researching and observing the universe. He claimed that objects that were located on the outskirts of the planets would “wander into the inner Solar System and become a comet” which was an explanation as to why there were no planets larger than Pluto past Neptune6.
Decades after Kuiper’s prediction, Julio Fernandez discussed the existence of this disc around the solar system and he believed that there must be a belt of comets due to the amount comets observed without the area. David Jewitt, an astronomer, and MIT astronomy student Jane Luu started to take advantage of telescopes of the Kitt Peak National and Cerro Tololo Inter-American Observatories to observe outside the depths of Neptune. After their five year search, Luu, and Jewitt disclosed the discovery of the first Kuiper Belt Object (KBO). About a half of a year later they found a second object and following that came many more6.
Canadian astronomers Martin Duncan, Scott Tremaine and Tom Quinn used a computer to simulate and proved that the Oort cloud was not responsible for all the short belt comets. However, Fernandez’s paper that suggested that there was a “belt” past Neptune, helped define the synonym which matched what astronomers of the past have said. The name the “Kuiper Belt”
was derived from Fernandez’ paper because, in the opening words of his thesis, he said “comet belt” and “Kuiper”6.
The Kuiper Belt Objects that have been discovered acknowledge that it’s possible that the belt could contain many more icy bodies that are variant in size. Currently, the Trans-Neptunian objects or the largest objects that are present in the belt are known as Pluto, Quaoar, Ixion, Varuna, and Haumea. Astronomers have been following short-period comets with their time frame being less than 200 years from where they originated in the Belt7 .\

Figure 3: Portrait of the Kuiper Belt, credits to of Space Facts

New Horizons Mission

New Horizons is the first mission to explore Pluto, its moons, the Kuiper Belt and all the icy bodies that reside inside of it. The spacecraft launched in 2006 and finally reached Pluto 9.5 years later in 2015. This sounds like a very long time, but in reality, New Horizons’ is the is the “fastest spacecraft to ever leave earth traveling at 36, 373 km/h”1 1 and traveled over 3 billion miles to reach Pluto.
In 2015 the spacecraft was able to reach this region, and capture the first ever close up pictures of a Kuiper Belt object, and images of the surface of Pluto. They discovered that despite Pluto’s size it is home to the largest ice glacier on any planet found in the solar system. The glacier ranges over 1 000 km, 4 km thick, and is estimated to be 4km thick”11.

Another unexpected discovery was the heart-shaped feature found on Pluto. The astronomers expected to discover amazing things, but they did not expect a “love note” back to Earth”8from the dwarf planet.

Nh-pluto-in-true-color 2x JPEG-edit-frame.jpg

By NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute –, Public Domain, Link



Near the heart-shaped crater, New Horizons was also able to get a close up look at the mountain ranges and peaks ranging “11,000” feet above Pluto’s surface. These results excited NASA’s research team because it is one of the youngest surfaces in the solar system “at only 100 million years old”11. After the flyby mission to Pluto and its many exciting discoveries, the go ahead was given to extend the New Horizons Mission. 

Missions Operations Manager Alice Bowman announced that the New Horizons mission will be exploring farther into the Kuiper Belt and has extended the mission until 2019. Vast and unexplored, the Kuiper belt is the source of many comets and contains ancient ice that was formed at the beginning of the Solar System. Let us hope New Horizons is just the beginning of future decades of research into this mysterious region.


Video: “Pluto, the Kuiper belt and the early history of the solar system” – Renu Malhotra (SETI Talks)

Who is Renu Malhotra?

Renu Malhotra is a professor at the University of Arizona and has recently been focusing on “the orbital migration history of the giant planets, chaos, and stability in the Kuiper belt, dynamics of near-Earth and main-belt asteroids, the meteoritic bombardment history of the terrestrial planets, and architectures of exosolar planetary systems”10. Her SETI talk has been included on this website because she gives a clear and concise explanation of the Kuiper Belt and Pluto and the important role they play in our solar system.
She says “Pluto is the “smoking gun” for some dramatic events that shaped our solar system long ago”. Renu Malhotra also explains that KBO objects are very interesting because “they are the leftovers of the building blocks of our solar system.
To conclude and answer the preliminary question, “What do astronomers know about the Kuiper Belt as well as the objects that belong to it, what methods did they use to discover these objects, and why?, it is very important to note that our universe is changing continuously and the methodology used by scientists to discover new astronomical objects is based on the criteria found on Pluto. The astronomers expected to discover amazing things, but they did not expect a “ love note” back to Earth”8 from the dwarf planet. Near the heart-shaped crater, New Horizons was also able to get a close up look at the mountain ranges and peaks ranging “11,000” feet above Pluto’s surface. These results excitedNASA’s research team because it is one of the youngest surfaces in the solar system “at only 100 million years old”11.  After the flyby mission to Pluto and its many exciting discoveries, the go-ahead was given to extend the New Horizons Mission.
and research was done previously by past astronomers. Without their research techniques our universe would still be constantly changing, but without recognition or evidence to be able to prove progression. The Kuiper Belt is a prime example of how research techniques like the ones used to discover Pluto, can lead to the discovery of additional astronomical objects.

Figures and Videos Video 1-–6Oi0&t=52s Video 2- “Pluto, the Kuiper belt and the early history of the solar system” – Renu Malhotra (SETI Talks) Video 3- Figure 1- Clyde Tombaugh and His Telescope O’Hara, Elva R. (2006). Clyde W. Tombaugh: Farm Boy Reached for the Stars. Borderlands 25. ved=0ahUKEwifp_nDyrLXAhXEKGMKHWu6CKAQpwUIHw&biw=1280&bih=649&dpr=1#i mgrc=61DxUDA9QSJqHM: Figure 2- Portrait of the Kuiper Belt, credits to of Space Facts Figure 3- File:The Kuiper Belt Orbits Pluto Polar.svg. (2015, November 4). Wikimedia Commons, the free media repository . Retrieved 01:04, December 1, 2017 from &oldid=177933287 .
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5. M. Brown, (2015). What is the Kuiper Belt ?. Accessed on November 09, 2017.–6Oi0&t=52s
6. B, Dunford, (2015). Kuiper Belt – In Depth | Planets – NASA Solar System Exploration. (n.d.). Accessed on November 09, 2017.
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8. C. Jones (2017). Kuiper Belt Facts Accessed on November 09, 2017, from
9. Keeter, Bill. “One Year Later: New Horizons’ Top 10 Discoveries at Pluto.” NASA. Accessed on November 28, 2017.
10. S.J. Peale, Nature 365, 788 (1993). Accessed on November 28, 2017. 11. “Renu Malhotra Webpage” Accessed on November 16,2017, 12. T. Talbert, NASA(2015). Accessed on November 16, 2017. 13. M. Moltenbrey, Dawn of small worlds: dwarf planets, asteroids, comets (Springer,
Cham, 2016). Accessed on November 09, 2017. pdf