7.4 Origin of the Solar System
3 min read•june 12, 2024
Our solar system's formation is a cosmic dance of gravity, collisions, and migration. Planets orbit in the same direction, with inner rocky worlds and outer gas giants. This pattern hints at a common birth from a spinning disk of material around our young .
Discoveries of diverse exoplanets have challenged our understanding of planet formation. , , and eccentric orbits show that planetary systems can take unexpected forms. These findings are reshaping theories about how worlds are born and evolve.
Solar System Formation
Key planetary characteristics for formation models
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- Orbital characteristics
- Planets orbit the Sun in the same direction () indicating they formed from a common rotating disk
- Planetary orbits are nearly circular (low eccentricity) suggesting a smooth formation process
- Planets orbit near the ecliptic plane (low inclination) supporting formation from a flattened disk
- Compositional characteristics
- Inner planets () are rocky and dense formed from high-temperature materials (iron, silicates)
- Outer planets () are gaseous and less dense accreted lighter elements (hydrogen, helium)
- Asteroid belt separates inner and outer planets marks transition in composition and formation conditions
- Rotational characteristics
- Most planets rotate in the same direction as their orbit (prograde) inherited from the rotating
- Rotational axes are tilted relative to the orbital plane () caused by collisions and gravitational interactions
- Satellite systems
- Regular satellites orbit in the same direction as the planet's rotation formed from material around the planet
- Irregular satellites have inclined, eccentric, and/or retrograde orbits captured by the planet's gravity
Extrasolar systems and formation understanding
- Diversity of extrasolar systems challenges traditional formation models
- : gas giants orbiting close to their stars (51 Pegasi b) require migration to explain their positions
- : planets larger than but smaller than Neptune (Kepler-10b) not found in our solar system
- Eccentric orbits: some exoplanets have highly elliptical orbits (HD 80606b) indicating dynamic interactions
- Migration explains unexpected orbital configurations
- Gravitational interactions can cause planets to migrate inward (hot Jupiters) or outward
- Protoplanetary disk interactions and drive migration ()
- provides an alternative formation mechanism for gas giants
- Gravitational instabilities in the protoplanetary disk can lead to rapid planet formation
- May explain some directly imaged giant planets ( system)
- remains the dominant formation mechanism for gas giants in our solar system
- Planetary cores form first, then accrete gas from the surrounding disk
- Explains the structure and compositions of and Saturn
Role of collisions in early solar system
- formation begins with collisions
- Collisions between dust grains lead to the growth of (kilometer-sized objects)
- Gravitational interactions cause to grow into protoplanets ( to -sized)
- Terrestrial planet formation proceeds through collisions
- Protoplanets collide and merge to form the terrestrial planets (, , Earth, Mars)
- Collisions result in the formation of the Moon (giant impact hypothesis)
- shaped the inner solar system
- Period of intense asteroid and comet impacts on the inner planets (~4.1 to 3.8 billion years ago)
- May have been caused by migration of the outer planets ()
- Asteroid belt structure is influenced by collisions
- Collisions between asteroids produce smaller fragments and dust ()
- Jupiter's gravity prevents asteroids from accreting into a single planet
- and are shaped by collisions and gravitational interactions
- Reservoirs of icy objects beyond Neptune's orbit (, )
- Collisions and gravitational interactions shape the structure of these regions
Formation and Evolution Processes
- initiates solar system formation
- Molecular cloud contracts under its own gravity, forming the protosun and protoplanetary disk
- shapes the disk structure
- As the cloud collapses, it spins faster, flattening into a disk
- determines planet composition
- Different materials condense at varying distances from the protosun based on temperature
- alters orbital configurations
- Planets can move inward or outward due to interactions with the disk or other planets
- Resonances between orbiting bodies influence system dynamics
- Orbital periods of planets or moons can form integer ratios, affecting their long-term stability
- creates layered internal structures
- As planets heat up, materials separate based on density, forming cores, mantles, and crusts
Key Terms to Review (48)
Accretion: Accretion is the process by which particles in space stick together to form larger bodies, such as planets and stars. This occurs through collisions and gravitational attraction, leading to the growth of celestial objects.
Accretion: Accretion is the process by which matter, such as dust, gas, or smaller objects, accumulates over time to form larger bodies, like planets, stars, or galaxies. It is a fundamental mechanism underlying the formation and growth of many celestial objects in the universe.
Angular Momentum Conservation: Angular momentum conservation is a fundamental principle in physics that states the total angular momentum of a closed system remains constant unless an external torque is applied. This principle is crucial in understanding the formation and evolution of celestial bodies, including the origin of the Solar System.
Catastrophism: Catastrophism is a geological theory that explains the origins and development of the Earth and its life forms through the occurrence of sudden, violent, and widespread events or catastrophes. It stands in contrast to the concept of uniformitarianism, which proposes that geological and biological changes occur gradually over long periods of time.
Condensation Sequence: The condensation sequence refers to the process by which various elements and compounds condense out of a cooling gas or plasma to form solid particles, such as dust grains, in the early stages of the formation of a planetary system. This sequence is a crucial concept in understanding the origin and evolution of the solar system.
Core Accretion: Core accretion is the theory that describes the formation of planets, particularly gas giants, through the gradual accumulation of solid materials and gas around a central core. It is a fundamental concept in understanding the origin and evolution of planetary systems, including our own Solar System.
Differentiation: Differentiation is the process by which a previously uniform structure or organism becomes specialized and diversified, often in the context of planetary and solar system formation. It involves the separation and development of distinct components or layers within a system, leading to increased complexity and specialization.
Disk Instability: Disk instability refers to a mechanism that can lead to the formation of planets and other objects in a protoplanetary disk around a young star. It describes the gravitational instability that can occur within the disk, causing it to fragment and collapse into dense clumps that may eventually form planets or other celestial bodies.
Earth: Earth is the third planet from the Sun and the only known planet in the universe to harbor life. It is the largest and densest of the inner planets, with a diverse range of geological features, a dynamic atmosphere, and a unique position in the Solar System that has enabled the development of complex life forms.
Eris: Eris is a dwarf planet in the outer Solar System, and the most massive and second-largest known dwarf planet in the Solar System after Pluto. It is a significant object in the context of understanding the formation and evolution of our planetary system.
Grand Tack Model: The Grand Tack model is a hypothesis that explains the formation and early evolution of the solar system. It proposes that the gas giant planets, particularly Jupiter and Saturn, underwent a complex inward-then-outward migration in the early stages of the solar system's development, significantly shaping the final architecture of the planets and their orbits.
Gravitational Collapse: Gravitational collapse is the process by which a massive object, such as a star or cloud of gas and dust, contracts under its own gravitational attraction. This contraction can lead to the formation of various celestial bodies and the release of tremendous amounts of energy.
Hot Jupiters: Hot Jupiters are a class of exoplanets that are similar in size and composition to Jupiter but orbit very close to their host stars. They typically have very high surface temperatures because of their proximity to the star.
Hot Jupiters: Hot Jupiters are a class of exoplanets that are similar in size to the planet Jupiter but orbit much closer to their host stars, typically less than 0.1 astronomical units (AU) from the star. These massive, gaseous planets have a profound influence on the understanding of planetary formation and evolution, as well as the comparison of planetary systems beyond our own Solar System.
HR 8799: HR 8799 is a young, massive star system located approximately 129 light-years from Earth. It is notable for hosting a directly imaged planetary system, which provides valuable insights into the formation and evolution of planetary systems beyond our own Solar System.
Immanuel Kant: Immanuel Kant was an influential German philosopher who lived in the 18th century. He is known for his groundbreaking work in the fields of metaphysics, epistemology, and ethics, which had a profound impact on the development of modern thought, including the understanding of the origin of the solar system.
Jovian: The term 'Jovian' refers to the large, gas-giant planets in our solar system, primarily Jupiter and the other outer planets. These planets are characterized by their massive size, primarily gaseous composition, and unique atmospheric features.
Jupiter: Jupiter is the largest planet in our solar system, a gas giant with a massive, turbulent atmosphere dominated by a giant, swirling storm known as the Great Red Spot. As the fifth planet from the Sun, Jupiter's immense size and powerful gravitational field have a profound influence on the dynamics and evolution of the entire solar system.
Kirkwood Gaps: Kirkwood gaps are regions in the asteroid belt where there is a noticeable lack of asteroids. These gaps occur at specific orbital distances from the Sun, where the orbital period of an asteroid would be a simple fraction of Jupiter's orbital period, leading to gravitational resonances that clear out material from these regions over time.
Kuiper belt: The Kuiper Belt is a region of the solar system beyond Neptune, populated with icy bodies and dwarf planets. It is the source of many short-period comets that orbit the Sun in less than 200 years.
Kuiper Belt: The Kuiper Belt is a region of the solar system beyond the orbit of Neptune, containing numerous small icy objects, including dwarf planets like Pluto. This belt of objects orbits the Sun and is considered an important feature in understanding the formation and evolution of the solar system.
Late Heavy Bombardment: The Late Heavy Bombardment (LHB) refers to a period in the early history of the Solar System, approximately 4.1 to 3.8 billion years ago, when the inner planets experienced an intense bombardment by a large number of asteroids, comets, and other planetesimals. This event had significant implications for the composition, structure, and evolution of the planets, as well as the development of life on Earth.
Mars: Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, after Mercury. It is often referred to as the 'Red Planet' due to its reddish appearance, which is caused by the iron oxide prevalent on its surface. Mars has a thin atmosphere and a diverse landscape, including volcanoes, canyons, and polar ice caps, making it a fascinating subject of study in the context of astronomy and the origin of the Solar System. The term 'Mars' is significant in the context of the topics 1.6 A Tour of the Universe, 7.4 Origin of the Solar System, 10.1 The Nearest Planets: An Overview, and 10.6 Divergent Planetary Evolution. As one of the terrestrial planets, Mars provides valuable insights into the formation and evolution of the Solar System, as well as the potential for life beyond Earth.
Mercury: Mercury is the closest planet to the Sun and the smallest of the eight planets in the Solar System. It is a terrestrial planet, meaning it has a solid surface, and is known for its dense composition, slow rotation, and extreme temperature variations.
Moon: The Moon is Earth's only natural satellite, a celestial body that orbits the planet and plays a crucial role in various astronomical and geological phenomena. It is a prominent feature in the night sky and has captivated humanity for millennia.
Nebular Hypothesis: The nebular hypothesis is a theory that explains the formation and evolution of the solar system. It proposes that the Sun and the planets originated from the gravitational collapse of a giant molecular cloud of gas and dust, known as a nebula.
Nice Model: The Nice model, also known as the Nice scenario, is a theoretical framework that explains the formation and evolution of the solar system. It provides a comprehensive model for the origin and distribution of the planets and other bodies in our solar system.
Obliquity: Obliquity refers to the tilt of a planet's rotational axis relative to its orbital plane around the sun. This angular difference between the planet's axis and the plane of its orbit is a crucial factor in determining the planet's climate and seasons.
Oort cloud: The Oort Cloud is a hypothetical, distant region of the Solar System that is believed to surround the Sun with a vast shell of icy bodies. It is thought to be the source of most long-period comets that enter the inner Solar System.
Oort Cloud: The Oort Cloud is a hypothetical spherical cloud of icy objects that is believed to surround the Solar System at a vast distance. It is considered the source of long-period comets that enter the inner Solar System. The Oort Cloud plays a crucial role in our understanding of the formation and evolution of the Solar System, as well as the origin and fate of comets and related objects.
Pierre-Simon Laplace: Pierre-Simon Laplace was a French mathematician and astronomer who made significant contributions to the understanding of the origin and evolution of the Solar System. He is best known for his work on the nebular hypothesis, which provided a comprehensive explanation for the formation of the planets and the Sun.
Planetary Migration: Planetary migration refers to the process by which planets can change their orbits around a star over time, often due to interactions with other planets or the protoplanetary disk during the formation of a planetary system. This concept is crucial in understanding the origin and evolution of our own solar system as well as other planetary systems beyond our Sun.
Planetesimal: A planetesimal is a small celestial body that forms during the early stages of planet formation in a protoplanetary disk. They are the building blocks of planets, created through the process of accretion and collision.
Planetesimals: Planetesimals are small celestial objects that formed from dust and gas in the early solar system. They serve as the building blocks of planets through a process called accretion.
Planetesimals: Planetesimals are the small, rocky or icy bodies that formed the building blocks of the planets in the early stages of the Solar System's development. These objects, ranging from just a few kilometers to hundreds of kilometers in size, gradually accumulated through the process of accretion to eventually create the larger planetary bodies we see today.
Pluto: Pluto is a dwarf planet located in the outer reaches of the Solar System. It was once considered the ninth planet from the Sun but was reclassified as a dwarf planet in 2006. Pluto's unique characteristics and its place in the Solar System make it an important object of study in various astronomical topics.
Prograde: Prograde refers to the direction of orbital motion that is in the same direction as the rotation of the central body. In the context of planetary systems, prograde motion is the direction of rotation and revolution that is the same as the spin of the host star or planet.
Protoplanetary Disk: A protoplanetary disk is a rotating circumstellar disk of dense gas and dust surrounding a young newly formed star. It is the birthplace of planets, where the material in the disk begins to coalesce under gravity to form a planetary system.
Radiometric Dating: Radiometric dating is a method of determining the age of rocks, minerals, and other geological materials by measuring the amount of radioactive decay that has occurred within them over time. This technique relies on the predictable rate at which certain radioactive isotopes decay into more stable daughter isotopes, allowing scientists to calculate the age of a sample based on the ratio of parent to daughter isotopes present.
Resonances: Resonances refer to the phenomenon where the gravitational influence of one celestial body causes periodic disturbances in the orbit of another body, leading to stable or unstable configurations. This concept is particularly important in understanding the origin and evolution of the solar system.
Solar nebula: A solar nebula is a rotating disk of gas and dust from which the Sun and planets formed about 4.6 billion years ago. It is the initial stage in the development of a solar system, where gravitational forces cause material to coalesce into various celestial bodies.
Solar Nebula: The solar nebula is the rotating cloud of dense gas and dust from which the Sun and the planets of the Solar System formed approximately 4.6 billion years ago. It is the initial state of the formation of the Solar System, providing the material and angular momentum that led to the development of the Sun and its orbiting planets.
Spectroscopic Analysis: Spectroscopic analysis is a technique that uses the interaction of electromagnetic radiation with matter to determine the chemical composition and physical properties of a substance. It involves the study and interpretation of the spectrum produced when light or other radiation interacts with a sample, providing valuable insights into the nature and characteristics of the observed object or phenomenon.
Sun: The Sun is the star at the center of the solar system, providing light, heat, and energy that sustains life on Earth. As the closest star to our planet, the Sun's gravitational influence shapes the orbits of the planets and other objects in the solar system, and its nuclear fusion powers the processes that drive the evolution of the universe.
Super-Earths: Super-Earths are exoplanets with a mass larger than Earth's but significantly less than that of ice giants like Uranus and Neptune. They can have a variety of compositions, including rocky, gaseous, or a mix of both.
Super-Earths: Super-Earths are exoplanets that are more massive than Earth, but less massive than Neptune or Uranus. These planets have a wide range of sizes, compositions, and potential habitability, and their study provides valuable insights into the formation and evolution of planetary systems beyond our own.
Terrestrial: Terrestrial refers to anything that is related to or associated with the Earth or its environment. It is a term that is commonly used in the context of astronomy and planetary science to distinguish objects or phenomena that are Earth-based or Earth-like from those that are extraterrestrial or occur in space beyond the Earth's atmosphere.
Venus: Venus is the second planet from the Sun and the closest planetary neighbor to Earth. It is often referred to as Earth's 'sister planet' due to their similar sizes and compositions. Venus has a unique and complex relationship with the topics of 1.6 A Tour of the Universe, 7.4 Origin of the Solar System, 10.1 The Nearest Planets: An Overview, 10.3 The Massive Atmosphere of Venus, and 10.6 Divergent Planetary Evolution.