Solar System Overview and Planet Classification

Solar System Overview

• The solar system includes the Sun and eight planets, and other celestial bodies like moons, asteroids, comets, meteoroids, dwarf planets, and meteorites.
• The Milky Way Galaxy contains an estimated 3,200 solar systems.
• The definition of a planet is in flux; current criteria: orbits the Sun, has enough gravity to take a spherical shape, and has cleared out its orbital path.

Defining Planets

• To be classified as a planet, a celestial body must meet specific criteria; orbit the Sun, have enough gravity for a spherical shape, and clear its orbital path.
• In 2006, Pluto was reclassified as a dwarf planet, reducing the number of known planets to eight.
• A common mnemonic for remembering the order of the planets is "My Very Educated Mother Just Served Us Nachos".

Planet Categorization

• Planets are categorized as either terrestrial or Jovian.
• Terrestrial planets (Mercury, Venus, Earth, Mars): solid surface, rocky composition, relatively smaller, metal core, have an atmosphere.
• Jovian planets (Jupiter, Saturn, Uranus, Neptune): gaseous composition, no solid surface, larger than terrestrial planets, nicknamed gas giants.

Moons

• Moons orbit planets, not the Sun, and are spherical due to their gravity.
• Earth has one prominent moon; some planets have no moons, others have multiple.
• Jupiter has an estimated 79 moons, with 53 confirmed by NASA.

Smaller Solar System Bodies

• Meteoroids: small celestial bodies floating in space.
• Asteroids: larger, rocky or metallic objects orbiting the Sun, often found in the asteroid belt; considered minor planets.
• Comets: icy bodies of gas, rock, and dust that orbit the Sun in elliptical paths; often develop tails as they approach the Sun. There are approximately 3,743 known comets (as of early 2022).

Meteors, Meteorites, and Meteoroids

• Meteoroids become meteors when entering Earth's atmosphere. Friction heats them up, creating a bright streak (shooting star).
• Most meteors disintegrate in the atmosphere.
• Remaining material that hits the ground is a meteorite.
• These are different stages of the same celestial body.