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Glossary term: Dwarf Planet

Description: A dwarf planet is a celestial body with the following properties: It orbits around the Sun, has enough mass to obtain a nearly round shape, has not cleared its path along its orbit, and is not a moon. Dwarf planets tend to orbit in regions made up of similar bodies, as in the case of the asteroid belt and Kuiper belt. In general, dwarf planets are smaller than Mercury, with icy, rocky structures. The amount of ice relative to the rocks depends on their position in the Solar System. Pluto is the most famous dwarf planet. The term dwarf planet should not be confused with the obsolete term minor planet.

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

The OAE Multilingual Glossary is a project of the IAU Office of Astronomy for Education (OAE) in collaboration with the IAU Office of Astronomy Outreach (OAO). The terms and definitions were chosen, written and reviewed by a collective effort from the OAE, the OAE Centers and Nodes, the OAE National Astronomy Education Coordinators (NAECs) and other volunteers. You can find a full list of credits here. All glossary terms and their definitions are released under a Creative Commons CC BY-4.0 license and should be credited to "IAU OAE".

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Image of Pluto in enhanced colour to bring out differences in surface composition. They include craters, ridges and plains.

Pluto

Caption: NASA's New Horizons spacecraft captured this high-resolution enhanced colour view of the dwarf planet Pluto on in July 2015. The image combines blue, red and infrared images taken by the Ralph/Multispectral Visual Imaging Camera (MVIC). Pluto’s surface appears enhanced in this view to a rainbow of pale blues, yellows, oranges, and deep reds. The image resolves details and colours on scales as small as 1.3 kilometers.
Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute credit link

License: PD Public Domain icons


The asteroid Ceres, roughly spherical with a grey surface, many craters, some of which reveal white subsurface water ice.

Ceres

Caption: True-colour image of the asteroid Ceres acquired by the spaceprobe Dawn in May 2015, at a distance of 13641 km. The prominent, bright crater at right is Haulani. The smaller bright spot to its left is exposed on the floor of Oxo. Ejecta from these impacts appears to have exposed bright material, probably water ice.
Credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA / Justin Cowart

License: CC-BY-2.0 Creative Commons Attribution 2.0 Generic icons


Graphics showing the Sun, the planets and the dwarf planet pluto with text in Arabic

Pluto: The Long Journey Around the Sun

Caption: This infographic is part of the "Simplifying Astronomy for Arabic Speakers" project, aiming to present fascinating facts about the dwarf planet Pluto and its long journey around the Sun. Pluto: The Mysterious Dwarf Planet Pluto is a dwarf planet that orbits the Sun within the Kuiper Belt, a region filled with icy and rocky objects beyond Neptune’s orbit. It was first discovered in 1930 by astronomer Clyde Tombaugh. For decades, Pluto was classified as the ninth planet in the Solar System, but in 2006, the International Astronomical Union (IAU) redefined the criteria for planets, placing Pluto in the dwarf planet category. A Very Long Orbital Journey Pluto takes 248 Earth years to complete a single orbit around the Sun! Since its discovery in 1930, it has not yet completed one full revolution. However, it will finally complete its first full orbit since its discovery on March 23, 2178. This means that future generations will witness this rare astronomical event. Pluto’s Unique Characteristics It has an average distance of 5.9 billion kilometers from the Sun. Pluto has a thin atmosphere composed mainly of nitrogen, methane, and carbon monoxide. It has five moons, the largest of which is Charon, forming a binary system with Pluto. Its surface is covered in ice, with vast nitrogen plains, such as the famous Tombaugh Region. Why Is Studying Pluto Important? Despite being classified as a dwarf planet, Pluto remains one of the most intriguing objects in the Solar System. NASA’s New Horizons mission (2015) provided breathtaking details about Pluto, helping scientists better understand its composition and history. Pluto is not just a distant dwarf planet; it serves as a window into the early formation of the Solar System. As research continues, this small world may reveal astonishing secrets about the origins of our planetary system and the universe itself.
Credit: Ali Al-Edhari

License: CC-BY-4.0 Creative Commons Attribution 4.0 International (CC BY 4.0) icons