Solar System Formation (Unit 3)

Protoplanet

A body that grows by the accumulation/accretion of planetesimals, but has not yet become big enough to be called a planet.

Protostar

A contracting cloud of gas and dust with enough mass to form a star; protostars form from nebulas.

Gravity

A force of attraction between objects. Small objects are attracted to larger ones, which causes objects to accrete and grow in size.

Supernova

A gigantic explosion in which a massive star collapses and throws its outer layers into space. This produces many heavy elements like gold, lead, and uranium.

Solar Nebula

A large cloud of gas and dust, such as the one that formed our solar system.

Atmosphere

A mixture of gases that surrounds a planet or moon. Inner planets have thin atmospheres. Outer planets have thick atmospheres.

Nebular Theory

A model for the beginning of the solar system that proposes a rotating nebula of gas and dust contracted to form the Sun and planets.

Celestial Body

A natural object in space, such as the sun, moon, a planet, or a star.

Gas Giant

A planet that has a deep, massive atmosphere, such as Jupiter, Saturn, Uranus, or Neptune.

Nuclear Fusion

A process that occurs in the core of stars; hydrogen is fused into helium and releases energy. A protostar becomes main-sequence when nuclear fusion begins in its core.

Protoplanetary Disk

A rotating disk of gas and dust particles surrounding a newly formed star or protostar. Over time, accretion within the disk tends to produce planets.

Solar System

A star and the celestial bodies that orbit around it. This includes, planets, dwarf planets, asteroids, planetesimals, comets, etc. Each star is part of its own solar system.

Planet

An object that orbits a star, is large enough to have become rounded by its own gravity, and has accreted all smaller objects from its orbit.

Planetesimal

One of the small asteroid-like bodies that formed the "building blocks" of the planets through accretion.

Accretion

The process of how planetesimals, protoplanets, and planets get larger; small materials "stick" to larger ones due to gravity.

Ice Giant

Planets with a higher amounts of frozen water, ammonia, and methane in their atmosphere; Uranus and Neptune.

Outer Planets

The four planets furthest from the Sun and outside the asteroid belt: Jupiter, Saturn, Uranus, Neptune.

Inner Planets

The four, small, rocky, planets that orbit closest to the Sun including Mercury, Venus, Earth, and Mars.