雅思阅读 088: When Humans Moved an Asteroid — NASA's DART Mission

Adapted from "NASA changed an asteroid's orbital path around the sun, a first for humankind" by Jackie Flynn Mogensen, Scientific American, 6 March 2026.

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Reading Passage

In September 2022, NASA did something no human had ever done: it deliberately crashed a spacecraft into a small asteroid. The rock, named Dimorphos, orbits a larger companion called Didymos as part of a binary pair. The mission, called DART (Double Asteroid Redirection Test), was designed to nudge Dimorphos off course and test whether such a method could one day defend Earth from a dangerous asteroid.

The collision worked. It slowed Dimorphos's orbit around Didymos by about 30 minutes. But scientists have now discovered that the impact did something even more remarkable: by slowing the inner moonlet, it altered the entire binary system's orbit around the Sun.

In a study published in Science Advances, researchers report that the pair's journey around the Sun slowed by about 12 micrometres per second — roughly 370 metres per year. Although tiny in astronomical terms, this is the first time humans have ever changed a natural object's orbit around our star.

"If an asteroid is ever on its way to hitting the Earth," says lead author Rahil Makadia of the University of Illinois Urbana-Champaign, "we can more confidently say that we have the ability to push them away."

DART involved ramming a 570-kilogram spacecraft into Dimorphos at about 22,530 kilometres per hour. The collision ejected rock and dust into space, and this ejected material contributed roughly as much momentum as the spacecraft itself — effectively doubling the push.

Makadia's team combined radar measurements with observations of the system as it passed in front of the Sun, comparing the asteroids' path before and after impact. They also estimated the mass of each asteroid separately for the first time.

The findings have broader value beyond planetary defence. Knowing the asteroids' mass and density helps scientists understand how binary asteroids form and what they are made of.

More data are on the way. Later this year, the European Space Agency's Hera mission will arrive at Didymos to photograph the impact crater and study the system in detail. "Once we get those measurements," Makadia says, "we can confirm our numbers from an independent angle."

The experiment proves that planetary defence is not just science fiction. It is a tested capability.

Questions 1–5

Choose the correct letter, A, B, C or D.

1. What was the name of the asteroid that DART crashed into?

   • A. Didymos
   • B. Dimorphos
   • C. DART
   • D. Hera

2. When did the DART impact occur?

   • A. September 2022
   • B. March 2026
   • C. November 2026
   • D. April 2029

3. The binary system's orbit around the Sun slowed by about

   • A. 30 minutes per year.
   • B. 12 micrometres per second.
   • C. 370 kilometres per hour.
   • D. 570 kilograms per second.

4. How heavy was the DART spacecraft?

   • A. 57 kilograms
   • B. 570 kilograms
   • C. 5,700 kilograms
   • D. 57,000 kilograms

5. The ejected rock and dust from the collision

   • A. had no effect on the orbit.
   • B. reduced the total push by half.
   • C. roughly doubled the total push.
   • D. fell back onto the asteroid immediately.

Questions 6–10

Do the following statements agree with the information?

Write:

• TRUE
• FALSE
• NOT GIVEN

6. Didymos and Dimorphos currently threaten Earth.
7. DART slowed Dimorphos's orbit around Didymos by about 30 minutes.
8. The research team measured the asteroids' masses before the impact.
9. ESA's Hera mission is already studying the impact crater.
10. The new study is the first to measure a change in a natural object's orbit around the Sun.

Questions 11–13

Complete the sentences. Choose NO MORE THAN TWO WORDS.

11. The DART spacecraft was travelling at roughly ________ kilometres per hour when it hit.
12. The ejected material roughly ________ the push from the spacecraft alone.
13. ESA's ________ mission will photograph the impact crater later this year.

Answers

1. B — "slamming into Dimorphos."
2. A — "In September 2022 NASA smashed a spacecraft into an asteroid."
3. B — "slowed the entire binary's solar orbit by around 12 microns per second."
4. B — "ramming a 570-kilogram spacecraft."
5. C — "It basically doubled the push from the spacecraft alone."
6. FALSE — "Dimorphos and Didymos don't pose a danger to Earth."
7. TRUE — "slowing its orbit around its bigger companion by around 30 minutes."
8. FALSE — The team estimated masses for the first time after the impact.
9. FALSE — Hera is due later this year, not yet arrived.
10. TRUE — "marks a first for humanity."
11. 22,530
12. doubled
13. Hera

Key Vocabulary