PHYSICS · Stage 8 · Chapter 10: The Earth in Space (Galaxies and Asteroids)
Physics 10.2 Asteroids — The Asteroid Belt, Meteoroids, Meteors and Meteorites
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Lesson summary
Physics 10.2 Asteroids — The Asteroid Belt, Meteoroids, Meteors and Meteorites — Alhussan International Academy — Physics (Stages 7–9) notes: Describe asteroids, how they form and the evidence for impacts, and distinguish asteroids, meteoroids, meteors, meteorites and comets.Aste…
- Solar System formation
- Leftover debris
- Other stars
- Near-Earth asteroids
- Classification
- Revising explanations
Section 1 of 6What an asteroid is
- Asteroid = a rock that orbits the Sun and is smaller than a planet.
- Some are large enough to be called minor planets.
- Size
- From less than 10 m to over 500 km in diameter.
- Shape
- Most are irregular, because their gravity is too weak to pull them into a sphere, though some are nearly spherical.
- Mass
- The total mass of all asteroids is less than the mass of the Moon.
- Moons
- More than 100 asteroids have moons of their own.
- Name
- "Asteroid" means "star-like shape", named over 200 years ago by someone who saw them only through a telescope.
Section 2 of 6How asteroids form
- Solar System formation
- Gravity pulled dust and gas together about 4.6 billion years ago.
- Leftover debris
- The pieces of rock that were left over are asteroids.
- Jupiter
- Its gravity may have broken up some smaller planets or stopped the material in the belt from joining into a planet.
- Other stars
- Most stars have planetary systems, which probably have asteroids for the same reason.
Section 3 of 6Where asteroids are
- Number
- There are over a million asteroids in our Solar System.
- Asteroid belt
- Most are between Mars and Jupiter, though some share an orbit with larger planets such as Jupiter.
- Near-Earth asteroids
- Some have orbits that bring them close to Earth, and astronomers track them to warn of a possible impact.
- Ceres
- The largest object in the belt is a dwarf planet.
Section 4 of 6Interstellar visitor
- 2017
- An object from interstellar space, ’Oumuamua, was detected in our Solar System for the first time.
- Classification
- Astronomers first thought it was a comet and then classified it as an asteroid.
- Revising explanations
- Scientists change a classification when new data do not fit.
Section 5 of 6Asteroid, meteoroid, meteor, meteorite and comet
| Object | Definition | Approximate size |
|---|---|---|
| Asteroid | A large piece of rock orbiting the Sun, smaller than a planet and larger than a meteoroid | Larger than a meteoroid |
| Meteoroid | A smaller piece of rock broken off from an asteroid or comet | 1 m in diameter or smaller |
| Meteor | A meteoroid that has entered the Earth's atmosphere, producing a streak of light | 1 m in diameter or smaller |
| Meteorite | A meteor that reaches the ground | 1 m in diameter or smaller |
| Comet | An object of ice and dust orbiting the Sun that grows a tail near the Sun | About 10 km in diameter |
- Atmosphere
- Friction heats a meteoroid so it glows, and most vaporise before reaching the ground.
Section 6 of 6Evidence for impacts
- Meteorites
- They are sometimes found on the ground.
- A 500 kg rock meteorite landed in Chelyabinsk, Russia, in 2013.
- A 37 g iron and nickel meteorite was found in Arizona, USA.
- Studying asteroids
- Telescopes and spacecraft that fly past or land on them show they are rock and metal fragments left from the early Solar System.
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