Solar System Formation and the Solar Nebular Theory

Vocabulary practice flashcards covering the formation of the solar system, patterns of planetary motion, nebular collapse, condensation, accretion, and exoplanet observations.

Solar Nebula

A large, diffuse interstellar gas cloud that collapsed under its own gravity to form our solar system, initially spanning a few light-years in diameter.

Conservation of Energy (in Nebular Collapse)

The physical process where the gravitational potential energy of infalling gas particles is converted into thermal energy (heat) through particle collisions.

Conservation of Angular Momentum (in Nebular Collapse)

The law dictating that the solar nebula rotated faster and faster as it shrank in radius, preventing all of the nebular material from collapsing onto the protosun.

Protosun

The hot, dense central concentration of mass formed during nebular collapse that eventually ignited nuclear fusion at its core to become a star.

Nebular Flattening

The formation of a rotating, flattened disk from a collapsing cloud caused by collisions between gas clumps that cancel out random motions and average orbital speeds.

Terrestrial Planets

The inner planets characterized by smaller sizes and masses, higher densities (made of rocks and metals), solid surfaces, warmer temperatures, few or no moons, and no rings.

Jovian Planets

The outer planets characterized by larger sizes and masses, lower densities, lack of a solid surface, cooler temperatures, many moons, and ring systems.

Asteroids

Rocky and metallic leftover planetesimals that reside primarily in the Asteroid Belt between the orbits of Mars and Jupiter.

Comets

Icy leftover planetesimals located predominantly in the Kuiper belt or the Oort cloud outside the orbit of Pluto.

Frost Line

The temperature boundary located between the Asteroid Belt and Jupiter beyond which hydrogen compounds condense into solid ice flakes.

Hydrogen Compounds

Substances such as water ($\text{H}_2\text{O}$), methane ($\text{CH}_4$), and ammonia ($\text{NH}_3$) that make up approximately $1.4\%$ of the solar nebula and condense at temperatures below $150\,\text{K}$.

Planetesimals

Solid bodies composed of rock, metal, or ice that formed by condensation and collided under gravity to build planets.

Accretion

The growth process in which solid condensation seeds and planetesimals collide, stick together, and attract more material through gravity.

Solar Wind

A strong outflow of charged particles from the young Sun that blew away excess, unaccreted gas from the nebula after about $10\text{ million years}$.

Era of Bombardment

An early phase of solar system evolution characterized by heavy collisions and impacts among leftover planetesimals and developing protoplanets.

Obliquity

The angle of tilt of a planet's rotation axis relative to the perpendicular of its orbital plane, typically measuring less than $25^\circ$ for most planets.

Comet Shoemaker-Levy 9

A comet that broke apart in July 1992 and collided with Jupiter in July 1994, demonstrating that planetary impacts continue after the early formation era.

Planetary Migration

The process where a planet gravitationally nudges disk material to bunch up, creating a dense region that pulls backward on the planet and causes it to spiral inward.

Transit Event

An astronomical event where an exoplanet passes directly in front of its parent star, causing a measurable dip in the star's observed brightness over time.

Hot Jupiters

Gas-giant Jovian planets that orbit extremely close to their central host stars, posing a challenge to nebular condensation models that require giant planets to form beyond the frost line.