Missions to asteroids
Spacecraft have now visited asteroids, brought back samples and even pushed one off course. This final lesson shows how missions test what meteorites taught us.
- Describe what sample-return missions to Ryugu and Bennu found.
- Explain how the DART mission tested planetary defence.
- Calculate a percentage change from mission data.
Links to: KS3 physics, space physics; working scientifically: how scientific ideas are tested; maths: percentage change and time units.
Bringing asteroids home
Meteorites are damaged by their fiery entry and contaminated once they land. Samples collected directly from an asteroid avoid both problems.
Japan's Hayabusa2 collected about 5.4 g from the asteroid Ryugu and returned it to Earth in 2020. NASA's OSIRIS-REx collected about 122 g from the asteroid Bennu and returned it in 2023. Both samples are dark, carbon-rich and full of clay minerals formed by water, closely matching the rarest carbonaceous chondrites. Bennu's sample also contains amino acids and salts left behind when salty water evaporated.
Pushing an asteroid
On 26 September 2022 NASA's DART spacecraft deliberately crashed into Dimorphos, a small moon about 150 m across that orbits the asteroid Didymos. Before the impact, Dimorphos took 11 hours 55 minutes to orbit. Afterwards it took about 33 minutes less. It was the first time humans had changed the motion of a natural body in space, showing that a well-timed nudge could one day steer a dangerous asteroid away from Earth.
The European Space Agency's Hera spacecraft, launched in 2024, is due to reach the pair in late 2026 to study the result in detail.
Science as a cycle
Meteorites suggested what asteroids are made of. Telescopes compared the colours of asteroids with meteorites in the laboratory. Missions then went to check, and largely confirmed the predictions, while also producing surprises, such as how loosely held together some asteroids are. That is how science works: ideas lead to predictions, and predictions are tested with new evidence.
How much did DART change the orbit?
Dimorphos's orbit took 11 hours 55 minutes before DART and about 33 minutes less afterwards. Calculate the percentage change.
- Convert the original period to minutes: 11 × 60 + 55 = 660 + 55 = 715 minutes.
- Percentage change = (change ÷ original) × 100 = (33 ÷ 715) × 100.
- 33 ÷ 715 ≈ 0.046, and 0.046 × 100 ≈ 4.6%.
Answer: The orbit period decreased by about 4.6%, far more than the minimum of about 73 seconds that the mission needed to count as a success.
Choose one mission from the space missions pages on this site. Make a one-page fact file with: the target, launch and arrival dates, what it did, one key result, and one question it raised. Then explain in two sentences how the mission tested an idea that first came from studying meteorites.
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 1Why are samples brought back from asteroids so valuable?
Sample-return capsules protect the material, so scientists can study it as it was in space.
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Question 2Which asteroid did OSIRIS-REx collect samples from?
OSIRIS-REx returned about 122 g from Bennu in 2023. Hayabusa2 sampled Ryugu.
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Question 3What did the DART mission do?
DART's deliberate impact in 2022 changed Dimorphos's orbit by about 33 minutes.
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Question 4What did the Ryugu and Bennu samples turn out to resemble?
Both were dark, carbon-rich and full of clay minerals, like carbonaceous chondrites.
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Question 5An orbit period changes from 600 minutes to 570 minutes. What is the percentage change?
The change is 30 minutes; 30 ÷ 600 × 100 = 5%, and the period got shorter.