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Physics LibreTexts

6: Solar System Formation and Other Stellar Systems

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This module introduces you to our solar system and how astronomers believe it formed, based on what we see around us and around other star systems in formation. We will also look at the discovery of other planets around other stars–called exoplanets.

Learning Objectives

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

  • Explain the nebular theory of the solar system formation
  • Describe the evidence which supports the nebular theory
  • List the IAU’s criteria to be a planet, and how this changed the status of Pluto
  • Explain what an exoplanet is, as well as the history of their discoveries
  • List examples of unusual stellar systems
  • Explain brown dwarfs and how they differ from stars and planets
  • Discuss stellar system habitable zones and what that has to do with life

  • 6.1: Our Solar System
    This page provides insights into the solar system's age, estimated at 4.6 billion years via meteorite studies and stellar observations. It outlines the components of the solar system, including the Sun, eight to ten planets, their moons, and minor bodies like asteroids and comets, along with regions such as the Kuiper Belt and the Oort cloud.
  • 6.2: The Nebular Theory
    This page explains the Nebular Theory, which describes how the solar system formed from a nebula, likely a supernova's remnants. As the nebula collapsed, a protostar emerged at its center, leading to the Sun's formation. The surrounding material flattened into a Protoplanetary Disk, facilitating the formation of planets. The current orderly motions in the solar system arise from the nebula's initial spinning and flattened state.
  • 6.3: What is a Planet?
    This page discusses the IAU's 2006 decision to classify Pluto as a dwarf planet due to its inability to clear its orbital neighborhood, reducing the solar system's planet count from nine to eight. This reclassification sparked ongoing debates in the scientific community, especially after the New Horizons mission, which focused on exploring Pluto and its moons.
  • 6.4: The Nebular Theory - Other Important Evidence
    This page discusses how the characteristics of solar system objects provide evidence for the Nebular Theory, highlighting the arrangement of planets, with rocky ones close to the Sun and gas giants further out. It notes the organized orbits of most objects and mentions anomalies such as Earth's large moon, Uranus's tilt, and Venus's retrograde rotation, which challenge expected patterns.
  • 6.5: The Nebular Theory - Proplyds
    This page supports the Nebular Theory through observations of gas and dust discs around stars, the existence of young planetary systems (Proplyds), and spiral galaxy formation. Computer modeling further simulates stellar system formation akin to our solar system.
  • 6.6: Systems and Extrasolar Planets
    This page explains extrasolar planets, or exoplanets, which are planets orbiting stars outside our solar system. The term "extrasolar" distinguishes them from planets in our solar system, which is named after our sun. Additionally, it mentions that systems with other stars are called stellar systems.
  • 6.7: The Discovery of Extrasolar Planets
    This page discusses Dr. Geoff Marcy's contribution to developing detection techniques for extrasolar planets in the late 1980s. By 2014, astronomers identified 1,822 planets in 1,137 systems, many larger and hotter than Earth and in close orbits. Technological advancements now allow both amateurs and professionals to observe these planets, with hopes for direct imaging in the future.
  • 6.8: The Kepler Mission
    This page discusses NASA's Kepler Mission, launched in March 2009, which aims to identify Earth-sized exoplanets using a space telescope that monitors 100,000 stars for changes in brightness. Named after Johannes Kepler, it primarily focuses on finding Earth-like planets despite the easier detection of gas giants. The content also includes a visual comparison of the sizes of exoplanets Kepler-20e and Kepler-20f relative to Venus and Earth.
  • 6.9: What We Have Learned about Stellar Systems and Extrasolar Planets?
    This page discusses the prevalence of binary and multiple star systems in the universe, noting that about half of stellar systems consist of binaries, while some contain three or more stars. An example provided is β Scorpii, which includes at least seven stars. The presence of these complex stellar systems is highlighted as a potential challenge for the emergence of intelligent life.
  • 6.10: The Circumstellar Habitable Zone
    This page discusses the circumstellar habitable zone, or Goldilocks Zone, where planets can hold liquid water. Though many exoplanets are found within this zone, some scientists propose that life may thrive beyond it, inspired by Earth's extremophiles. It’s estimated that one in five stars hosts an Earth-sized planet in this zone, indicating up to 40 billion possible habitable planets in the Milky Way.
  • 6.11: Some Interesting Exoplanets
    This page discusses several exoplanets, highlighting TrES-4, which is larger but less massive than Jupiter with a low density, and planets in the Gliese 581 system, including HD80606b with extreme temperatures and high mass, and Wasp-12b, which has an extremely short orbital period and is being consumed by its star. The page concludes with a note on the conditions necessary for the existence of intelligent life, emphasizing the importance of stars, planets, and their distances.
  • 6.12: Extrasolar Planets
    This page examines Brown Dwarf Gliese 229B and its relevance to solar system formation. It notes the discovery of exoplanets, some larger than Jupiter and orbiting close to their stars, indicating possible migration in their formation. The text discusses brown dwarfs—objects that are too light for hydrogen fusion—questioning their classification as planets or failed stars. It also references Giordano Bruno's controversial idea that stars are distant suns with their own planets.


This page titled 6: Solar System Formation and Other Stellar Systems is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Lumen Learning via source content that was edited to the style and standards of the LibreTexts platform.

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