Overview
This lecture covered the origins, characteristics, and impacts of meteoroids, meteors, meteorites, asteroids, and comets in our solar system, including their composition, classification, and effects on Earth.
Origins and Types of Space Debris
- Meteoroids are small rocks or debris in space, before entering Earth's atmosphere.
- When a meteoroid enters the atmosphere and produces a visible streak, it is called a meteor.
- If any piece of a meteoroid survives and lands on Earth's surface, it is called a meteorite.
- Meteor showers occur when Earth passes through debris left by comets.
Asteroids
- Asteroids are rocky or metallic bodies, mostly located between Mars and Jupiter in the main asteroid belt.
- The main asteroid belt contains millions of objects, but is mostly empty space.
- Types of asteroids include carbonaceous (carbon-rich), siliceous (rocky), and metallic (iron/nickel-rich).
- Some asteroids have moons or exist as binary systems.
- Near-Earth asteroids (NEAs) are those whose orbits bring them close to Earth's orbit.
- Trojans are asteroids sharing an orbit with a larger planet, clustered 60° ahead or behind the planet.
Meteorites: Composition and Classification
- Meteorites fall into three main classes: iron, stony, and stony-iron.
- Iron meteorites are metal-rich, durable, and easier to identify.
- Stony meteorites can be divided into chondrites (contain small glassy spheres called chondrules) and achondrites (do not contain chondrules).
- Carbonaceous chondrites are rich in water and organic materials.
- Meteorites provide insights into early solar system conditions.
Comets
- Comets are icy bodies mixed with dust and rock, often called "dirty snowballs."
- When near the Sun, comets form a glowing coma and typically two tails: an ion (gas) tail and a dust tail.
- Comet tails always point away from the Sun due to solar wind and radiation.
- Short-period comets come from the Kuiper Belt; long-period comets originate from the Oort Cloud.
- Comets can bring organic compounds and possibly water to planets.
Impacts and Historical Events
- Most meteors burn up in the atmosphere, but large impacts can form craters (e.g., Barringer Crater, Vredefort Dome).
- The 1908 Tunguska event and the dinosaur extinction event were caused by large impacts.
- Jupiter’s gravity helps protect Earth by capturing or deflecting many incoming objects.
- Impact events can cause dramatic climate changes by blocking sunlight and disrupting ecosystems.
Key Terms & Definitions
- Meteoroid — a small rock or particle in space.
- Meteor — the light phenomenon (shooting star) when a meteoroid enters Earth's atmosphere.
- Meteorite — a meteoroid fragment that lands on Earth.
- Asteroid — a rocky or metallic object orbiting the Sun, mostly in the asteroid belt.
- Comet — an icy, dusty object from the outer solar system that develops tails when near the Sun.
- Chondrite — a stony meteorite containing small spherical inclusions (chondrules).
- Near-Earth Object (NEO) — asteroid or comet with orbit bringing it close to Earth's orbit.
- Trojan asteroid — asteroid sharing a planet’s orbit at stable Lagrange points.
Action Items / Next Steps
- Review the classification of meteorites and differences between meteoroid, meteor, and meteorite for exams.
- Look for announcements about observing the currently visible comet.
- Optional: Research Antarctic meteorite expeditions or careers in space research.
- Read textbook chapters on solar system formation and planetary impacts as referenced in class.