The Solar System: Planets and Classifications

Vocabulary flashcards covering key planets, their features, classifications, and notable terms from the lecture notes.

Pluto

A dwarf planet in the Kuiper Belt; once considered the ninth planet, reclassified by the IAU in 2006 for not clearing its orbit; has five moons (Charon, Styx, Nix, Kerberos, Hydra).

Kuiper Belt

A region beyond Neptune populated by icy bodies; home to Pluto and other dwarf planets; source of some comets.

IAU definition of a planet

A celestial body that orbits a star, is spherical due to its gravity, and has cleared its orbital path of debris.

Neptune

The eighth planet; an ice giant with rings; discovered via mathematical prediction; extremely cold (~-218°C); has 14 known moons, including Triton.

Great Dark Spot

Neptune’s storm observed by Voyager 2; notably temporary and has since disappeared.

Uranus

The seventh planet; an ice giant with an axial tilt of about 98°, causing a sideways rotation; discovered in 1781 by William Herschel; blue‑green color from methane; has many moons and faint rings.

Uranus axial tilt

Approximately 98°, causing the planet to roll around the Sun rather than spin upright.

Olympus Mons

Largest volcano in the Solar System, located on Mars; about three times taller than Mount Everest.

Mars

Terrestrial planet with a thin atmosphere, seasons, and notable volcanoes like Olympus Mons; about 1.52 AU from the Sun; past evidence of water; extreme day–night temperature differences.

Jupiter

The largest planet; a gas giant composed mostly of hydrogen and helium; about 143,000 km in diameter; ~318 Earth masses; rotates in ~10 hours; orbits the Sun every ~12 years.

Great Red Spot

A gigantic, centuries‑old storm on Jupiter.

Saturn

A gas giant famous for its prominent ring system; about 9.58 AU from the Sun; hexagonal storm at the north pole; many moons, including Titan.

Titan

Saturn’s largest moon; thick atmosphere and potential liquid on its surface.

Ring system

Rings composed of ice and rock particles that surround many gas giants.

Triton

Neptune’s largest moon; known for its activity and retrograde orbit.

Terrestrial planets

Rocky, solid-surface planets with small size, thin or no atmospheres, and few moons (Mercury, Venus, Earth, Mars).

Gas giants

Planets dominated by hydrogen and helium, lacking solid surfaces, with thick atmospheres, many moons, and ring systems.

Two types of planets

Terrestrial (rocky) planets and gaseous (gas giant) planets.

Mercury

Closest planet to the Sun; smallest terrestrial planet; very thin atmosphere; extreme temperature differences; no moons.

4.6 billion years

Age of the Solar System; all planets formed around 4.6 billion years ago.

Dwarf planet

A celestial body that orbits the Sun, is spherical due to gravity, but has not cleared its orbital path.

Voyager 2

NASA spacecraft that provided key observations of outer planets, including Neptune’s Great Dark Spot.

Neptune’s moons count

Neptune has 14 known moons; the largest is Triton.

Neptune’s winds

Winds can reach ~2,100 km/h (1,300 mph) on Neptune.

Neptune’s orbital period

Takes about 165 Earth years to complete one orbit around the Sun.

Uranus’ color origin

The blue‑green color of Uranus is due to methane in its atmosphere.

Neptune’s discovery note

Neptune was discovered based on mathematical predictions rather than direct observation.