Composition and Formation of the Universe and Solar System

A collection of vocabulary terms and definitions regarding cosmological theories, the formation of the solar system, and the specific characteristics of terrestrial planets.

Cosmology

The science that provides hypotheses explaining the beginning of the universe based on its present physical and chemical properties.

Big Bang Theory

The prevailing cosmological model for the early development of the universe, suggesting it expanded from a hot, dense state.

Cosmic Microwave Background (CMB)

Considered the oldest light in the universe, it is a thermal radiation remnant from an early stage of the universe's development used in observational cosmology.

Age of the Universe

Currently measured to be approximately $13.82$ billion years.

Cosmic Inflation Theory

A theory proposed by Alan Guth and Andrei Linde stating that the early universe underwent a rapid expansion of space-time fueled by pure vacuum energy.

Steady State Theory

An obsolete theory proposing that the universe is always expanding but maintains a constant appearance because new matter is continuously created.

Quasars and Radio Galaxies

Galactic bodies whose distant locations provided evidence contradicting the Steady State Theory, implying the universe is dynamic rather than unchanging.

Star System

Also called a stellar system, it consists of a small number of stars that orbit each other.

Nebular Hypothesis

The theory that the solar system formed around $4.5$ billion years ago from a rotating cloud of extremely hot gas called a nebula.

Planetesimal Theory

States that planets formed from the accretion of small space bodies, where gravity attracted objects until they increased in size.

Tidal Theory

A theory suggesting that a passing star's gravitational pull drew matter out of the sun, which then cooled and clumped to form planets.

Inner Planets

Also known as terrestrial or telluric planets (Mercury, Venus, Earth, and Mars), characterized by compact, rocky surfaces and silicate internal structures.

Outer Planets

Also known as Jovian or "gas planets" (Jupiter, Saturn, Uranus, and Neptune), they are larger, less dense, and composed primarily of hydrogen and helium.

Frost Line

The distance from the sun beyond which temperatures were low enough for gases to condense, leading to the formation of giant gas planets.

Mercury

The smallest and closest terrestrial planet to the Sun, featuring a massive iron core and lacking a substantial atmosphere.

Venus

The second planet from the Sun, known for its dense carbon dioxide atmosphere, extreme runaway greenhouse effect, and surface temperatures averaging $464^\text{o}\text{C}$.

Retrograde Motion

The phenomenon observed on Venus where its extremely slow rotation causes the Sun to rise in the west.

Earth

The only terrestrial planet with abundant liquid water covering approximately $70$% of its surface and an atmosphere rich in nitrogen and oxygen.

Plate Tectonics

The process of moving plates on Earth's outer crust that constantly recycles the surface and erases impact craters.

Mars

Known as the "Red Planet" due to iron oxide in its soil, it is considered the most habitable planet other than Earth in the solar system.

Sol

A Martian day, which lasts approximately $24$ hours and $37$ minutes.

Phobos and Deimos

The two small, irregularly shaped moons of Mars, believed to be captured asteroids.

Olympus Mons

The largest volcano in the solar system, located on Mars, towering at $21.9\text{ km}$.

Valles Marineris

A vast canyon system on Mars over $4,000\text{ km}$ long and up to $7\text{ km}$ deep.