13.1 Other Bodies in the Solar System
Besides planets and moons, the Solar System contains smaller celestial bodies: meteoroids, asteroids, and comets.
1. Meteoroid
- Definition: Small bits of rock or metallic debris floating in outer space (ranging from small pebbles to around 10 meters in diameter).
- Origin: Fragmented pieces from asteroid collisions or debris left behind by comets.
- Stages of a Meteoroid:
- Meteoroid: Body while still floating in outer space.
- Meteor ("Shooting Star"): When a meteoroid enters Earth's atmosphere at high speed, friction with atmospheric gases generates extreme heat, causing it to burn and glow, creating a streak of light.
- Meteorite: If a meteoroid is large enough to survive atmospheric burn up and hits Earth's surface, the remaining rock is called a meteorite. Impact can create a crater.
2. Asteroid
- Definition: Large, irregular, rocky, and metallic bodies orbiting the Sun that are smaller than planets (ranging from 1 meter to hundreds of kilometers in diameter). Also known as minor planets.
- Location: Most asteroids are located in the Asteroid Belt situated between the orbits of Mars and Jupiter.
- Examples: Ceres (largest asteroid/dwarf planet), Pallas, Vesta, and Eros.
- Asteroid Orbit Collisions: Gravitational nudges from giant planets (like Jupiter) can push asteroids out of the belt, putting them on potential collision courses with Earth.
3. Comet
- Definition: Small celestial bodies made of frozen gases (water ice, carbon dioxide, methane, ammonia), dust, and rocky debris ("dirty snowballs").
- Origin: Originate from the distant outer regions of the Solar System — the Kuiper Belt and the Oort Cloud.
- Orbit: Highly elliptical (oval) orbits around the Sun.
- Structure when Approaching the Sun:
- Nucleus: Solid core of ice and dust.
- Coma: Glowing cloud of gas and dust surrounding the nucleus created as solar radiation sublimates the surface ice.
- Tail: Pushed away from the Sun by solar wind and radiation pressure. Always points DIRECTLY AWAY from the Sun, regardless of the comet's direction of motion.
- Example: Halley's Comet (appears every 75–76 years).
13.2 Earth Collisions with Meteoroids, Asteroids, and Comets
- Atmospheric Protection: Earth's atmosphere acts as a protective shield; friction burns up most incoming small meteoroids into harmless meteors.
- Impact Consequences: Large asteroids or meteorites colliding with Earth can cause catastrophic consequences: giant impact craters, mass extinctions (e.g., the extinction of non-avian dinosaurs 66 million years ago), global dust clouds blocking sunlight, acid rain, and massive tsunamis.