Rocks in Space
🎯 In this topic you will
- Discover that asteroids are rocks that are smaller than planets
- Understand that scientists believe asteroids are leftover rocks from the formation of the Solar System
🧠 Key Words
- asteroid belt
- asteroids
- craters
- impacts
Show Definitions
- asteroid belt: A region of space between Mars and Jupiter where most asteroids in the Solar System are found.
- asteroids: Small rocky objects that orbit the Sun and are usually irregular in shape.
- craters: Bowl-shaped holes on a surface caused by collisions with space objects like asteroids.
- impacts: Collisions between asteroids or other objects and a planet or moon, often forming craters.
🌍 What Are Asteroids?
Asteroids are objects made from rock that orbit the Sun. They range in size up to 975 km across, with the smallest studied asteroid being just 2 m across. Most asteroids are irregular in shape, similar to how rocks on Earth are not regular shapes. Scientists often describe asteroid shapes as resembling potatoes.
🧪 Did you know?
Although most asteroids orbit between Mars and Jupiter, some pass close to Earth — and scientists track thousands of these near-Earth objects to protect our planet.
🌌 Location of Asteroids in the Solar System
Most asteroids in the Solar System orbit the Sun between the orbits of Mars and Jupiter. This region is called the asteroid belt. There are millions of asteroids, and some have been studied and named.
📌 Important Concept
Asteroid Belt: A region of space between Mars and Jupiter where most asteroids orbit the Sun, forming a wide band of rocky debris in our Solar System.
🪐 Ceres: The Largest Asteroid
Ceres is the largest known asteroid and was discovered in 1801. At the time, scientists believed it was a new planet, but because it was much smaller than a planet, the term "asteroid" was introduced. Ceres appears round and is 975 km in diameter. It has a core, mantle, and crust, similar to planets, and is covered in craters. Scientists believe it could have become a planet if it had continued growing during the early formation of the Solar System.
🔎 Asteroid Itokawa and What It's Made Of
Itokawa is one of the smallest asteroids visited by a spacecraft. It measures about 530 m in length and 250 m in width. In 2005, a spacecraft collected surface samples from Itokawa, helping scientists learn more about how the Solar System formed.
Itokawa is made of loose lumps of rock, likely fragments from other bodies such as planets or moons. These pieces are held together by weak gravitational forces, since the asteroid is so small. When it passes near large objects, tidal forces can reshape it. Some asteroids, in contrast, are made of a single solid rock and spin quickly.
🌍 Asteroids and Their Impact on Earth
Scientists estimate that a large asteroid hits Earth roughly once every 130,000 years. However, smaller asteroids impact the Earth much more frequently. Many of these small asteroids break up in the atmosphere and never reach the surface.
Asteroids impact Earth for two main reasons: Earth’s strong gravitational pull and the fact that many asteroids have orbits that bring them close to our planet.
⚠️ Common Mistake
Don’t assume asteroids only hit Earth by chance — Earth’s gravity actually pulls nearby asteroids closer, increasing the likelihood of impacts.
❓ QUESTIONS
1. Describe what is meant by the term ‘asteroid’.
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2. Some asteroids have diameters between 300 and 500 m.
Explain why these asteroids are classed as small objects in the Solar System.
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3. The asteroid Ceres is covered with craters.
Suggest how these craters were formed.
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4. Describe where the rocks came from to form asteroids.
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🔬 Think like a Scientist
Question: What happened at Tunguska?
In this investigation, you will look at evidence that supports or contradicts hypotheses.
Method:
- Read these facts.
- Tunguska is in northern Russia, far from any towns or cities. There is forest there, with many trees.
- In the morning of 30 June 1908 there was a very large explosion at Tunguska, between 5 km and 10 km above the ground.
- People living over 800 km away could see and hear the explosion.
- Vibrations from the explosion were recorded almost 5000 km away.
- The explosion flattened trees over an area of 2000 km².
- Read these five hypotheses of what caused the explosion.
- A comet impacting the Earth.
- A type of volcano erupting.
- Testing of a new type of bomb.
- An alien spacecraft crashing.
- An asteroid impacting the Earth.
- Consider the evidence.
- All the trees that fell are pointing outwards from a central position.
- People discovered how to make very powerful bombs in 1945.
- No bomb this powerful has ever been made.
- Tunguska is very far from tectonic plate boundaries.
- Most comets break up higher than 10 km in the atmosphere.
- A small part of a comet is made from rock.
- Small rocky fragments have been found that show signs of falling through the atmosphere at very high speed.
- No metal parts have been found at Tunguska.
Questions:
Write about each hypothesis in turn.
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- Comet: Contradicted. Comets typically break up higher in the atmosphere. While some are partially rocky, most are not dense enough to cause this kind of explosion.
- Volcano: Contradicted. Tunguska is far from tectonic boundaries and has no volcanic activity.
- New bomb: Contradicted. No bombs of that power existed in 1908; nuclear weapons were not developed until 1945.
- Alien spacecraft: Contradicted. No metal debris or technological parts were ever found at the site.
- Asteroid: Supported. The rocky fragments, blast pattern, and atmospheric entry evidence all support an asteroid impact.
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Peer-assessment: