Solar Nebular Theory Lecture Notes

Vocabulary flashcards covering key terms, scientists, and processes related to the Solar Nebular Theory.

Solar Nebular Theory

The leading scientific model for Solar System formation, stating that the Sun and planets formed 4.6 billion years ago from a rotating cloud of gas and dust.

Nebular Hypothesis

An earlier name for the Solar Nebular Theory that envisions a contracting, rotating nebula giving birth to the Sun and planets.

Solar nebula

The original rotating cloud of gas and dust from which the Sun and its planetary system condensed.

Giant molecular cloud

A vast, cold interstellar cloud rich in hydrogen and helium whose collapse initiated formation of the solar nebula.

Protosun

The hot, dense core at the center of the collapsing nebula that eventually ignited to become the Sun.

Protoplanetary disk

The flattened, rotating disk of gas and dust surrounding the protosun where planets, moons, and other bodies formed.

Planetesimal

Kilometer-sized solid body created when dust and ice grains stuck together; foundational building block of planets.

Protoplanet

A larger embryonic planet produced by the accretion of planetesimals, precursor to a fully formed planet.

Accretion

The gradual growth of celestial bodies through collisions and sticking of smaller particles.

Condensation (planet formation)

Cooling process in the nebula that allowed materials to solidify and begin clumping into planetesimals.

Rocky planets

The inner Solar System worlds—Mercury, Venus, Earth, and Mars—made mostly of silicate rock and metal.

Immanuel Kant

German Enlightenment philosopher who outlined the first modern nebular hypothesis in 1755.

Pierre-Simon Laplace

French polymath who refined Kant’s nebular hypothesis in 1796 with a detailed collapsing-disk model.

Viktor Safronov

Soviet astronomer who, in the 1960s, supplied the mathematical framework for planetesimal accretion, shaping the modern theory.

James Jeans

English physicist and astronomer who researched gravitational collapse of nebulae and developed Jeans Length and Jeans Mass concepts.

Emanuel Swedenborg

Swedish scientist who, in 1734, first suggested that the Solar System formed from a rotating gas cloud.

Nicolaus Copernicus

Renaissance astronomer whose 1543 work established the heliocentric (Sun-centered) model.

Johannes Kepler

Early-17th-century astronomer who showed planets move in elliptical orbits around the Sun.

Galileo Galilei

Italian scientist who used telescopic observations (e.g., Jupiter’s moons) to confirm heliocentrism.

Planetesimal Hypothesis

Early-20th-century alternative by Chamberlin & Moulton proposing planets formed from numerous small bodies; later rejected.

Tidal Theory

Obsolete model by Jeans & Jeffreys suggesting planets formed from material tidally stripped from the Sun during a stellar encounter.

Jeans Length

Critical size beyond which a gas cloud segment becomes gravitationally unstable and collapses.

Jeans Mass

Minimum mass a gas cloud fragment must have to overcome pressure and undergo gravitational collapse.

Jeans Theorem

Principle in stellar dynamics that describes equilibrium distributions of stars in a galaxy.

Interstellar dust

Microscopic solid particles in space whose discovery helped modernize the nebular hypothesis.

Molecular cloud

Dense region of interstellar gas and dust—birthplace of stars and the likely origin of our solar nebula.

Geocentric model

Ancient cosmology placing Earth at the center of the universe, advocated by Aristotle.

Heliocentric model

Sun-centered structure of the Solar System advanced by Copernicus and validated by Kepler and Galileo.

Accretion disk

Rotating disk of matter spiraling into a central object; in early Solar System, synonymous with the protoplanetary disk.

Collisional growth

Process in which dust grains and planetesimals collide and merge, leading to increasingly larger bodies.