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9: Minor Bodies of the Solar System

Last updated

Jul 23, 2025
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- 8.11: Gas Giant Planets and Select Satellites Overviews
- 9.1: Trans-Neptunian objects, the Kuiper Belt, and the Oort Cloud

Lumen Learning
Lumen Learning

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Learning Objectives

Upon completion of this module, the student will be able to:Upon completion of this module, the student will be able to:

Differentiate between the types of minor bodies found in our solar system
List the characteristics of asteroids, including Near-Earth Asteroids (NEOs) and Potentially-Hazardous Asteroids (PHAs)
Differentiate among meteoroids, meteors, and meteorites
List the characteristics of three types of meteorites
List the characteristics of comets
List the characteristics of centaurs
Explain the discoveries of Pluto and Eris
List the characteristics of the Trans-Neptunian objects, Kuiper Belt and the Oort Cloud

This module explores the minor bodies of the solar system: asteroids, comets, and dwarf planets, as well as meteors and meteorites.

9.1: Trans-Neptunian objects, the Kuiper Belt, and the Oort Cloud
This page discusses Trans-Neptunian objects (TNOs), which are minor planets beyond Neptune, including Pluto and Eris. Over 1,500 TNOs have been cataloged, with around 200 classified as dwarf planets. Astronomers study their properties from Earth. The Kuiper Belt, situated 30 to 50 AU from the sun, contains KBOs, which comprise rock, metal, and ice. While all TNOs are KBOs, not all KBOs are TNOs.
9.2: The Oort Cloud and Kuiper Belt
This page discusses the Oort Cloud, a theoretical spherical region of icy objects located up to 50,000 AU from the sun, which is considered the primary source of long-period comets. No Oort Cloud Objects (OCO) have been discovered yet, and the Oort Cloud is believed to delineate the outer boundary of the solar system.
9.3: What do you think?
This page discusses how ancient people, without scientific knowledge, feared comets like Hale-Bopp because of their striking visibility. This phenomenon likely stirred strong emotions and influenced daily life, beliefs, and interpretations of omens in their societies.
9.4: Minor Bodies
This page discusses minor bodies in the solar system, which include small, irregularly shaped objects like asteroids, comets, and meteoroids, as well as Kuiper Belt and Oort Cloud Objects. These bodies are smaller than planets and have distinct orbits. It also mentions minor planets, a specific subset encompassing dwarf planets, centaurs, and trans-Neptunian objects, formed from remnants of the solar nebula.
9.5: Asteroids
This page discusses asteroids, minor solar system bodies similar to rocky planets. Ceres, the first and largest discovered asteroid, was reclassified as a Dwarf Planet in 2006. Most asteroids are irregularly shaped and orbit in the asteroid belt between Mars and Jupiter, acting as remnants from the solar system's formation. They contribute to meteorite impacts on Earth and some have satellites, with over 150 identified companions.
9.6: Brightest Asteroids Visible from Earth
This page provides data on celestial bodies, including asteroids and a dwarf planet. It includes their visual magnitudes and diameters: (4) Vesta (5.1 magnitude, 326 miles), (2) Pallas (6.4 magnitude, 338 miles), (1) Ceres as a dwarf planet (6.7 magnitude, 590 miles), (7) Iris (6.7 magnitude, 149 x 124 x 124 miles), and (433) Eros (6.8 magnitude, 21 x 7 x 7 miles).
9.7: Asteroid Classification
This page describes the classification of asteroids in the solar system into three groups: the Main Asteroid Belt between Mars and Jupiter, containing 1 to 2 million asteroids; Trojan Asteroids that share orbits with larger planets like Jupiter; and Near-Earth Asteroids (NEAs), with about 10,000 discovered, including over 1,400 Potentially Hazardous Asteroids.
9.8: Meteoroids, Meteors, and Meteorites
This page clarifies the differences between meteoroids, meteors, and meteorites, noting that meteoroids are smaller space materials, meteors are visible streaks in the sky, and meteorites are those that land on celestial bodies. Additionally, it mentions Thomas Jefferson's skepticism regarding meteorites.
9.9: Meteorites
This page explains the significance of meteorites in understanding the early solar system, categorizing them into three main types: stony (94% of samples), iron, and stony iron. Stony meteorites are rich in silicates and metals, while iron meteorites are dense and made primarily of iron and nickel. Stony irons, the rarest type, uniquely combine both characteristics and include Pallasites, which feature an appealing metal-nickel matrix surrounding olivine crystals.
9.10: The Impact of Meteorites
This page discusses three notable meteorite impact incidents: the 1908 Tunguska event, which devastated a vast area in Russia without any meteorite recovery; the 1947 Sikote-Alin impact, noted for an air burst that released significant meteoritic iron; and the 2013 Chelyabinsk event, which injured many and caused extensive building damage, resulting in the recovery of several stone meteorites.
9.11: Comets
This page discusses comets, termed "dirty snowballs," which are ice and dust compositions. About 5,000 comets have been identified, fewer than asteroids, and they mainly orbit in the Kuiper Belt and Oort Cloud on elliptical paths. Named after their discoverers, comets have historical significance and can collide with planets, as evidenced by Comet Shoemaker-Levy 9's impact on Jupiter in 1994. David Levy likened comets to cats for their unpredictable behavior.
9.12: Comet Characteristics
This page discusses the composition and behavior of comets, highlighting their role in meteor showers and their structures, including the nucleus, coma, and tail. It notes that comets are made of various materials and can behave unpredictably due to solar interactions. Observations of comet nuclei, such as Halley and Tempel-1, are mentioned, along with the European Space Agency's Rosetta mission targeting Comet Churyumov-Gerasimenko for landing.
9.13: Images of Comets
9.14: Comets in History
This page discusses the historical documentation of comets, starting with early Chinese observations. Aristotle's misconception classified comets as atmospheric phenomena. For centuries, comets were seen as bad omens, linked to disasters and political turmoil, as noted by Pliny the Elder. Halley’s Comet's appearance during the Battle of Hastings in 1066 exemplifies the connection between comets and major historical events.
9.15: Scientific Advances
This page outlines the historical progression of comet observation, starting with Tycho Brahe's 1577 measurements that indicated comets exist beyond Earth's atmosphere. Isaac Newton's Law of Universal Gravitation later linked comets to parabolic orbits. In the 18th century, Edmund Halley analyzed centuries of observations, identified three comets with similar orbits, and predicted the return of one in 1758-1759, which was validated, leading to the naming of Halley’s Comet.
9.16: Halley’s Comet
This page discusses Halley's Comet, observed since at least 240 BC and identified by Edmund Halley in the 17th century. Its 1910 passage led to scientific discoveries and public panic over cyanogen gas, resulting in comet-related products. The first spacecraft encounter occurred in 1986 during its least visible passage in 2,000 years. The next close approach is expected in July 2061.
9.17: A Comet Impacts a Planet
In 1994, Comet Shoemaker-Levy 9 collided with Jupiter, marking the first observed extraterrestrial impact. Discovered in 1993, the comet fragmented due to Jupiter's gravitational pull, resulting in twenty-one recorded impacts from July 22-26, 1994. These events produced visible fireballs and dark spots, enhancing astronomers' understanding of similar features on the Moon and other celestial bodies.
9.18: The Centaurs- Are they Asteroids or Comets?
This page discusses the discovery of Centaurs, celestial objects that possess features of both asteroids and comets, with around 44,000 believed to exist between Jupiter and Neptune. Named after mythological hybrids, these objects have water ice and comet-like tails, while resembling asteroids in composition. Chiron is highlighted as the most notable centaur, though no close-up images have been taken of these objects.
9.19: Pluto
This page discusses Pluto, discovered in 1930 and named after the Roman god of the underworld. Its classification as a planet is debated due to its comet-like characteristics and unusual orbit, which crosses Neptune's path. Pluto has five moons, including Charon, which is similar in size. The arrival of NASA's New Horizons mission in 2015 aims to clarify several uncertainties surrounding this celestial body.
9.20: Eris
This page discusses Eris, also known as Planet X or 2003 UB313, discovered by Dr. Mike Brown in 2003 and confirmed in 2005. It is located 14.5 billion kilometers from the sun, has a highly tilted orbit, and a diameter of approximately 2,326 kilometers, making it similar in size to Pluto. Eris is considered a large icy body and has a moon named Dysnomia, which is about 250 kilometers in diameter.

Learning Objectives

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