Planets of the Solar System

A comprehensive set of vocabulary flashcards covering the formation of the solar system, historical models of planetary motion, and the specific characteristics of inner and outer planets.

Solar System

The sun and all of the planets and other bodies that travel around it.

Planet

A celestial body that orbits the sun, is round because of its own gravity, and has cleared the neighborhood around its orbital path.

Solar Nebula

A rotating cloud of gas and dust from which the sun and planets formed.

Nebular Hypothesis

The hypothesis advanced by Pierre-Simon, marquis de Laplace, stating that the sun and planets condensed at about the same time out of a rotating cloud of gas and dust.

Sun Formation Temperature

The temperature at the center of the solar nebula reached approximately $10,000,000\,^{\circ}C$, triggering the beginning of hydrogen fusion.

Planetesimal

A small body from which a planet originated in the early stages of development of the solar system.

Protoplanets

Larger bodies formed when planetesimals joined together through collisions and gravity.

Differentiation

The process by which denser materials, such as molten iron, sank to the center of developing Earth, while less dense materials were forced to the outer layers.

Outgassing

The process by which volcanic eruptions released large amounts of gases, such as water vapor, carbon dioxide, nitrogen, and methane, to form a new atmosphere.

Ozone

A molecule containing three oxygen atoms that collected in a high atmospheric layer to shield Earth from harmful ultraviolet radiation.

Geocentric Model

An Earth-centered model of the solar system suggested by Aristotle where the sun, stars, and planets revolved around Earth.

Retrograde Motion

A pattern where planets sometimes appear to move backward in the sky relative to the stars.

Epicycles

Small circles in which planets move as they revolve in larger circles around Earth, proposed by Ptolemy to explain retrograde motion.

Heliocentric Model

A sun-centered model of the solar system proposed by Nicolaus Copernicus in 1543 CE.

Law of Ellipses

Kepler’s first law, stating that each planet orbits the sun in an elliptical path, not a circle.

Eccentricity

The degree of elongation of an elliptical orbit, denoted by the symbol $e$, calculated by dividing the distance between foci by the length of the major axis.

Law of Equal Areas

Kepler’s second law, stating that equal areas are covered in equal amounts of time as an object orbits the sun.

Orbital Period

The time required for a body to complete a single orbit.

Law of Periods

Kepler’s third law, stating that the cube of the average distance ($a$) of a planet from the sun is proportional to the square of the orbital period ($p$), expressed as $K \times a^3 = p^2$.

Inertia

The tendency of an object to resist a change in motion unless an outside force acts on the object.

Terrestrial Planet

One of the highly dense planets nearest to the sun; includes Mercury, Venus, Earth, and Mars.

Greenhouse Effect

Heating caused when a high concentration of carbon dioxide blocks infrared radiation from escaping a planet’s atmosphere.

Runaway Greenhouse Effect

The phenomenon on Venus that makes its average surface temperature $464\,^{\circ}C$, the highest in the solar system.

Olympus Mons

The largest volcano on Mars, standing nearly $24\,km$ tall and which is three times as tall as Mount Everest.

Gas Giant

A large planet with a deep, massive atmosphere made mostly of gas, such as Jupiter, Saturn, Uranus, or Neptune.

Great Red Spot

A giant rotating storm on Jupiter that has been raging for at least several hundred years and is twice the diameter of Earth.

Kuiper Belt

A region of the solar system starting just beyond the orbit of Neptune containing dwarf planets and small bodies made mostly of ice.

Dwarf Planet

An object that orbits the sun and is round because of its own gravity, but has not cleared the region around its orbit and is not a satellite of another planet.

Exoplanet

A planetlike object that orbits a star other than Earth’s sun.