Pluto: Discovery, Characteristics, and Dwarf Planet Status
This paper provides an overview of Pluto, the solar system's largest known dwarf planet, tracing its discovery by Clyde Tombaugh in 1930 at the Lowell Observatory in Arizona. It examines competing hypotheses about Pluto's origin, the historical search for "Planet X" initiated by Percival Lowell, and the eventual naming of Pluto by an Oxford schoolgirl. The paper also describes Pluto's distinctive physical and orbital characteristics, including its elliptical orbit, extreme temperatures, geological features, five known moons, and tenuous atmosphere. It concludes with the International Astronomical Union's 2006 decision to reclassify Pluto as a dwarf planet and the subsequent New Horizons mission that provided detailed observations of the distant body.
- Introduction: Pluto as a Puzzling Planet: Pluto's identity as a distant dwarf planet
- Theories on Pluto's Origin: Competing hypotheses about how Pluto formed
- Discovery of Pluto and Its Naming: Tombaugh's discovery and the naming process
- Physical and Orbital Characteristics: Pluto's size, orbit, mass, and distance from sun
- Geology and Atmosphere: Surface features, temperatures, and thin atmosphere
- Reclassification and Exploration: IAU's 2006 demotion and New Horizons mission
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What makes this paper effective
- The paper moves logically from historical discovery to physical description to modern reclassification, giving readers a coherent narrative arc about Pluto's evolving status in astronomy.
- It balances scientific data — orbital distances, mass figures, temperature ranges, and density values — with accessible historical storytelling, such as the naming suggestion by an 11-year-old Oxford schoolgirl.
- Multiple competing origin hypotheses are acknowledged and evaluated, demonstrating awareness that scientific understanding of Pluto remains contested and evolving.
Key academic technique demonstrated
The paper effectively uses footnoted citations in Chicago author-date style to anchor factual claims — particularly NASA data and scholarly sources — to specific references, lending credibility to quantitative assertions about Pluto's size, orbit, and atmospheric composition. This technique shows how even a descriptive survey paper benefits from systematic sourcing of empirical claims.
Structure breakdown
The paper is organized into six thematic sections: a brief introduction establishing Pluto's identity and puzzling status; a survey of origin hypotheses; the historical narrative of discovery and naming; a detailed profile of physical and orbital properties; an analysis of geology and atmosphere; and a final section on the IAU's 2006 reclassification and the New Horizons mission. Each section builds on the previous, moving from "what is Pluto and where did it come from?" toward "what do we now know and how did its status change?"
Introduction: Pluto as a Puzzling Planet
Pluto — nicknamed the "puzzling planet" or "runaway planet" — was discovered by Clyde Tombaugh, a young American astronomer, at the Lowell Observatory in Arizona in 1930. Pluto is the largest known dwarf planet and the ninth largest object directly orbiting the sun. It is the coldest, smallest, and most distant planet from the sun. Similar to other Kuiper Belt objects, Pluto's landscape consists mainly of rock and ice. Astronomers have long been puzzled by the origin of Pluto, with earlier work suggesting that it is a residual planetesimal.
Theories on Pluto's Origin
There are varied hypotheses about Pluto's origin. One possibility is that Pluto was knocked out of its original position by Neptune's largest moon, Triton, implying that Pluto never possessed fully planetary status. This concept was later rejected, however, as subsequent research established that there is no meaningful interaction between Neptune's and Pluto's orbits. Another strand of hypothesis argues that the formation of a distant rocky core in the Sun's protoplanetary disc resulted in the emergence of Pluto.
J. Hunter Waite Jr. and Christopher Glein proposed a cosmochemical model arguing that Pluto is essentially a giant comet containing gas and ice. The discovery of Pluto's place in astronomical history also traces back to the earlier discovery of Uranus by Sir William Herschel in the late eighteenth century — a finding that revealed a world beyond Saturn, which had for centuries been recognized as the outermost planet. Urbain Le Verrier's subsequent identification of Neptune, based on perturbations observed in Uranus's orbit, further fueled the drive for exploration that ultimately led to the discovery of Pluto.
Theorizing that puzzling perturbations in the orbits of Neptune and Uranus were caused by the gravitational influence of an unknown planetary body, Percival Lowell — founder of the famous Flagstaff Observatory in Arizona — proposed the existence of a ninth planet, which he called Planet X.
Bibliography
Ley, Willy. 1956. The Demotion of Pluto. New York: Galaxy Publishing Corp.
NASA Science. 2019. Solar System Exploration. April 25th. Accessed April 27, 2019. https://solarsystem.nasa.gov/planets/dwarf-planets/pluto/in-depth/.
Stern, S., F. Bagenal, K. Ennico, and George Gladstone. 2015. "The Pluto System: Initial Results from Its Exploration by New Horizons." Science vol. 350, issue 6258.
Stern, A., and J. Mitton. 2005. Pluto and Charon: Ice Worlds on the Ragged Edge of the Solar System. Wiley-VCH, 1997.
Tombaugh, Clyde, and Patrick Moore. 1980. Out of the Darkness: The Planet Pluto. Harrisburg: Stackpole Books.
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