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10.2Chapter 10: The Earth in Space (Galaxies and Asteroids)

Asteroids — Alhussan Physics - Stage 8 Revision Notes & Topical Questions

5 min read 8 parts Lesson 2 of 5 1 quiz

📚 Alhussan Physics - Stage 8 Hub / Topical Revision
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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

Part 1 of 6What an asteroid is

Asteroid
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.

Part 2 of 6How asteroids form

How 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.

Part 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.

Part 4 of 6Interstellar visitor

Interstellar 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.

Part 5 of 6Asteroid, meteoroid, meteor, meteorite and comet

ObjectDefinitionApproximate size
AsteroidA large piece of rock orbiting the Sun, smaller than a planet and larger than a meteoroidLarger than a meteoroid
MeteoroidA smaller piece of rock broken off from an asteroid or comet1 m in diameter or smaller
MeteorA meteoroid that has entered the Earth's atmosphere, producing a streak of light1 m in diameter or smaller
MeteoriteA meteor that reaches the ground1 m in diameter or smaller
CometAn object of ice and dust orbiting the Sun that grows a tail near the SunAbout 10 km in diameter
  • Atmosphere
    • Friction heats a meteoroid so it glows, and most vaporise before reaching the ground.

Part 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.

Key terms

TermMeaning
AsteroidA rocky object orbiting the Sun, smaller than a planet.
MeteoroidA small piece of rock in space.
MeteorThe streak of light when a meteoroid enters the atmosphere.
MeteoriteA meteor that reaches the ground.
CometAn object of ice and dust that develops a tail near the Sun.
Asteroid beltThe region between Mars and Jupiter containing most asteroids.

Avoid these mistakes

1
Thinking asteroids are small stars — they are rocks, not stars.
2
Thinking all meteors reach the ground — only meteorites do.
3
Thinking asteroids are the same as comets — comets are ice and dust with a tail.
4
Thinking the Moon is an asteroid — it orbits a planet and is much larger.

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