Rocks from the Moon and Mars
A few meteorites have come from the Moon and from Mars. In this lesson you will find out how a rock can escape a world and how scientists know where it came from.
- Explain how a rock can be blasted off the Moon or Mars.
- Describe how scientists know a meteorite came from Mars.
- Compare Moon rocks brought by astronauts with Moon meteorites.
Links to: Year 5 science, Earth and space: the Moon and planets; Year 3 science, rocks; maths: division and averages.
Blasted into space
When a big asteroid smashes into the Moon or Mars, the impact throws rock in all directions. A tiny amount is thrown so fast that it escapes the pull of gravity completely and flies off into space. To escape Mars, rock must reach about 5 kilometres every second. The Moon's gravity is weaker, so rock escapes at about 2.4 kilometres per second.
The rocks then travel around the Sun, sometimes for millions of years, until a few happen to meet Earth.
Proof from the gas inside
In 1976 two Viking spacecraft landed on Mars and measured the gases in its air. Later, scientists found tiny pockets of gas trapped inside some meteorites. The gas closely matched the air on Mars, and was quite unlike Earth's air. That proved these meteorites came from Mars.
One of the most famous Martian meteorites, Nakhla, fell in Egypt in 1911. Scientists have since found minerals in it that formed in water, showing that water once flowed through rocks on Mars.
Moon rocks
Between 1969 and 1972, astronauts on six Apollo missions brought back about 382 kilograms of Moon rock. Scientists compared those samples with strange meteorites found in Antarctica and saw that they matched. The meteorites were pieces of the Moon.
Meteorites from the Moon are useful because they come from all over its surface, including places no astronaut has visited.
Sharing out the Moon rock
Six Apollo missions brought back about 382 kg of Moon rock. On average, about how much did each mission bring back?
- An average shares the total equally, so divide by the number of missions: 382 ÷ 6.
- 6 × 60 = 360, which leaves 382 − 360 = 22.
- 6 × 3 = 18, which leaves 22 − 18 = 4. So 382 ÷ 6 = 63 remainder 4, which is about 63.7.
Answer: About 64 kg per mission on average. In fact the later missions, with a moon buggy to drive around, brought back much more than the first ones.
Draw a comic strip in four boxes showing the journey of a Mars meteorite: an asteroid hits Mars, a rock flies into space, it travels around the Sun, and it falls to Earth as a fireball. Add a caption to each box using words from this course.
Quiz
5 questions. Choose an answer to see whether you are right and why. Finish the quiz to complete the lesson.
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Question 1How can a rock get from Mars to Earth?
Only a huge impact can throw rock fast enough to escape Mars's gravity. No person has yet brought rock back from Mars.
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Question 2How did scientists prove some meteorites came from Mars?
The Viking landers measured the Martian air in 1976. Gas trapped in certain meteorites matches it closely.
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Question 3About how much Moon rock did the Apollo astronauts bring back?
Six Apollo missions between 1969 and 1972 brought back about 382 kg of rock and soil.
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Question 4Why do scientists value Moon meteorites as well as Apollo samples?
Apollo landed in only six places, all on the side of the Moon facing Earth. Meteorites can come from anywhere on the Moon.
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Question 5Why does rock escape the Moon more easily than Mars?
The Moon is smaller, so its gravity is weaker, and rock needs only about 2.4 km per second to escape, compared with about 5 km per second for Mars.