Our solar system's formation is a cosmic tale of gravity, motion, and composition. It all started with a rotating disk of gas and dust that collapsed, giving birth to the Sun and planets. The inner planets formed rocky and small, while the outer giants grew massive and gaseous.
The story doesn't end there. After formation, our cosmic neighborhood experienced a tumultuous period called the . Giant planets migrated, stirring up and . These events shaped the solar system we see today, leaving clues in the form of craters and planetary compositions.
Key Constraints and the Solar Nebula
Constraints on solar system formation
Motion
Orbits nearly circular and in the same plane indicate a common origin from a rotating disk of gas and dust
Planets orbit the Sun in the same direction () suggests they formed from material orbiting in the same direction
Most planetary orbits are nearly circular (low ) and in the same plane (low ) implies a flattened disk structure
Rotation in the same direction as orbits supports formation from a rotating disk
The Sun rotates in the same direction as the planetary orbits (prograde) indicates a shared angular momentum from the
Most planets rotate in the same direction as they orbit (prograde) with the exception of Venus and Uranus which may have undergone collisions or other events
Composition
Inner planets (terrestrial) are rocky and small compared to outer planets () which are gaseous and large
Rocky composition of inner planets (metals and silicates) suggests they formed in a higher temperature region where could not condense
Relatively small size and mass of compared to gas giants indicates a smaller supply of material in the inner solar system
Outer planets (gas giants) are gaseous and similar in composition to the Sun
Gaseous composition of outer planets (hydrogen and helium) matches the composition of the Sun and suggests they formed from the same material
Relatively large size and mass of gas giants implies a greater abundance of material in the outer solar system
Solar composition is mostly hydrogen and helium like the gas giants
Sun is composed primarily of hydrogen and helium which matches the composition of the gas giants and supports a common origin
Similar composition between the Sun and gas giants indicates they formed from the same source material in the
Age
of meteorites provides a lower age limit for the solar system
Meteorites are the oldest known solid objects in the solar system with ages around 4.6 billion years from radiometric dating
Age of meteorites provides a lower limit on the age of the solar system since they formed early in its history
Solar system formation occurred relatively quickly based on the age of meteorites and the Sun
Quick formation within ~100 million years is inferred from the ancient age of meteorites at 4.6 billion years
Rapid formation is also supported by models of star formation and the estimated age of the Sun
Changes in solar nebula
Gravitational collapse of the initial cloud of gas and dust (solar nebula) formed a flattened rotating disk
Nebula began to collapse under its own gravity which increased its density and triggered further collapse
Rotation of the nebula caused it to flatten into a disk shape () due to conservation of angular momentum
Heating and cooling of the nebula occurred as it collapsed and the Sun formed
Gravitational energy was converted to heat as the nebula collapsed causing the temperature to increase
Center of the nebula became hot enough for nuclear fusion to begin which marked the birth of the Sun
Outer regions of the disk cooled allowing solid particles to condense from the gas
Particle growth proceeded as solid particles collided and stuck together
Solid particles in the disk collided and formed larger particles through electrostatic forces and gravitational attraction
Continued growth of particles led to the formation of which are the building blocks of planets
Clearing of the disk occurred as planets formed and removed gas and dust
Newly formed planets gravitationally interacted with the remaining gas and dust in the disk
Gas was either accreted onto the planets or expelled from the system by solar radiation and winds
Dust was incorporated into planets or removed from the system leaving behind the planets and other objects
Planet Formation and Evolution
Terrestrial vs giant planet formation
Terrestrial planet formation occurred in the inner solar system where high temperatures prevented volatile condensation
Inner solar system had higher temperatures that only allowed metals and silicates to condense into solid particles
Lack of volatile compounds (water, methane) in the inner solar system limited the size of
Solid particles collided and merged to form which continued to grow through
Giant planet formation occurred in the outer solar system where volatiles could condense
Lower temperatures in the outer solar system allowed volatile compounds to condense in addition to metals and silicates
Abundance of icy particles and planetesimals provided more material for planet growth
model suggests giant planets formed in two stages:
Icy planetesimals collided to form solid cores of about 10 Earth masses
Cores then rapidly accreted gas from the surrounding disk to form massive atmospheres
model proposes an alternative formation mechanism for gas giants
Differences in composition reflect the formation conditions in the inner and outer solar system
Terrestrial planets are composed mainly of metals and silicates due to high temperature formation
Giant planets have a gaseous composition (hydrogen and helium) similar to the Sun with presumed rocky/icy cores
Post-formation solar system events
Late Heavy Bombardment (LHB) was a period of intense asteroid and comet impacts on the terrestrial planets
LHB occurred approximately 4.1 to 3.8 billion years ago based on the dating of lunar impact basins
Intense bombardment may have been caused by the migration of the giant planets which disrupted asteroid and comet orbits
LHB had significant effects on the terrestrial planets including crater formation and delivery of water and organic molecules to Earth
Giant planet migration is thought to have occurred after their formation
Giant planets likely formed closer to the Sun and then migrated outward to their current positions
Migration was driven by gravitational interactions with the remaining gas and dust in the protoplanetary disk
Outward migration of Jupiter and Saturn may have triggered the LHB by disturbing the orbits of asteroids and comets
Formation of the and from scattered remnants of the protoplanetary disk
is a spherical region of icy objects (comets) at the outer edge of the solar system up to a light-year from the Sun
is a disk-shaped region of icy objects (dwarf planets, comets) beyond the orbit of Neptune
Both regions formed from icy planetesimals that were gravitationally scattered outward by the giant planets
Planetary into distinct layers (core, mantle, crust) driven by internal heat
Differentiation is the separation of a planet's interior into layers based on density
Heat from radioactive decay and kinetic energy of drove differentiation
Denser materials (metals) sank to the center to form the core while lighter materials (silicates) rose to form the mantle and crust
Differentiation led to the formation of Earth's magnetic field and onset of plate tectonics
Solar System Formation Theory
The provides a comprehensive framework for understanding solar system formation
explains the flattening of the solar nebula into a disk and the prograde rotation of most planets
The describes how different materials solidified at varying distances from the Sun, influencing planet composition
played a crucial role in shaping the final architecture of the solar system
Key Terms to Review (34)
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.
Asteroids: Asteroids are small, rocky bodies that orbit the Sun, primarily found in the asteroid belt between Mars and Jupiter. They vary in size and shape, with some being large enough to be considered dwarf planets if they were spherical.
Comets: Comets are icy celestial bodies that orbit the Sun and exhibit a visible atmosphere or coma and sometimes a tail when they come close to the Sun. They originate from the outer regions of the Solar System, primarily the Kuiper Belt and Oort Cloud.
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.
Eccentricity: Eccentricity is a measure of how much an orbit deviates from being a perfect circle. It ranges from 0 (a perfect circle) to 1 (a parabolic trajectory).
Eccentricity: Eccentricity is a measure of how elliptical or elongated the orbit of a celestial body, such as a planet or comet, is around its parent body. It describes the degree to which an orbit deviates from a perfect circle, with a value ranging from 0 for a perfect circle to 1 for a parabolic orbit.
Gas Giants: Gas giants are the largest planets in our solar system, characterized by their massive size, predominantly gaseous composition, and unique atmospheric features. These planets play a crucial role in understanding the formation and evolution of our solar system, as described in the topics 10.1 The Nearest Planets: An Overview, 10.6 Divergent Planetary Evolution, 11.1 Exploring the Outer Planets, 11.2 The Giant Planets, and 14.3 Formation of the Solar System.
Gravitational Instability: Gravitational instability is a fundamental concept that describes the process by which matter in the universe, from the formation of the solar system to the evolution of galaxies, becomes organized into structures under the influence of gravity. It is a critical mechanism that drives the formation and evolution of celestial bodies and large-scale structures in the cosmos.
Inclination: Inclination refers to the angle between the orbital plane of a celestial body and a reference plane, typically the ecliptic or the equatorial plane. It is a crucial parameter that describes the orientation of an object's orbit within a larger system, such as the Solar System.
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.
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.
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.
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.
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.
Protoplanet: A protoplanet is a large planetary embryo that originated within a protoplanetary disk. It is in the process of developing into a fully-fledged planet through accretion and collisions with other celestial bodies.
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.
Saturn’s rings: Saturn's rings are a collection of countless small particles of ice and rock that orbit Saturn. They are the most extensive and complex ring system in our 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.
T Tauri Phase: The T Tauri phase is a critical stage in the formation of a young star, where the star is still contracting and accreting material from its surrounding protoplanetary disk. This phase is named after the prototype T Tauri variable star, which exhibits characteristic variability and other observable features during this evolutionary stage.
Terrestrial planets: Terrestrial planets are rocky planets with solid surfaces, located in the inner part of our solar system. They include Mercury, Venus, Earth, and Mars.
Terrestrial Planets: Terrestrial planets are a class of planets that are characterized by their solid, rocky surfaces and relatively small sizes compared to the gas giant planets. These planets, which include Mercury, Venus, Earth, and Mars, are the innermost planets in our solar system and share similar physical and geological characteristics.
Volatiles: Volatiles are chemical substances that have a high vapor pressure and low boiling point, causing them to evaporate or sublimate readily at normal temperatures and pressures. In the context of the formation of the solar system, volatiles play a crucial role in the composition and evolution of planetary bodies.