NASA’s DART mission, short for Double Asteroid Redirection Test, was the first full-scale test of changing an asteroid’s motion by spacecraft impact. It targeted Dimorphos, a small asteroid moon orbiting the larger asteroid Didymos. The goal was not to destroy the asteroid, but to slightly change its orbit in a measurable way.
This matters because a small velocity change made early enough could help prevent a future hazardous asteroid from hitting Earth.
DART used kinetic impact, meaning the spacecraft transferred momentum by deliberately crashing into Dimorphos at high speed. Before impact, Dimorphos orbited Didymos once every 11 hours 55 minutes, and after impact its orbital period became shorter by about 33 minutes. Telescopes on Earth measured this change by tracking the brightness pattern of the Didymos system.
The mission showed that asteroid deflection is a practical planetary defense technique when the target is found early and observed carefully.
Key Facts
- DART stands for Double Asteroid Redirection Test.
- Target system: Didymos is the larger asteroid, and Dimorphos is its smaller moon.
- DART impact speed was about 6.6 km/s, which is about 6600 m/s.
- Momentum is p = mv, where m is mass and v is velocity.
- Kinetic energy is KE = 1/2 mv^2, so high speed greatly increases impact energy.
- Dimorphos orbit period changed from about 11 h 55 min to about 11 h 22 min after impact.
Vocabulary
- Planetary defense
- Planetary defense is the study and practice of finding, tracking, and possibly deflecting objects that could collide with Earth.
- Kinetic impactor
- A kinetic impactor is a spacecraft designed to change an object’s motion by crashing into it at high speed.
- Momentum
- Momentum is the quantity of motion an object has, equal to mass times velocity.
- Orbital period
- Orbital period is the time it takes an object to complete one full orbit around another object.
- Binary asteroid
- A binary asteroid is a pair of asteroids where one object orbits the other.
Common Mistakes to Avoid
- Thinking DART was meant to blow up Dimorphos. The mission tested a small orbit change by momentum transfer, not asteroid destruction.
- Confusing Didymos with Dimorphos. Didymos is the larger parent asteroid, while Dimorphos is the smaller moon that DART struck.
- Using mass alone to judge impact effectiveness. Momentum depends on both mass and velocity, so DART’s high speed was essential.
- Assuming a tiny velocity change is useless. Over long times and distances, a small deflection can grow into a large change in position.
Practice Questions
- 1 DART had a mass of about 580 kg and struck Dimorphos at about 6600 m/s. Calculate the spacecraft’s momentum using p = mv.
- 2 Using the same mass and speed, calculate DART’s kinetic energy using KE = 1/2 mv^2.
- 3 Explain why changing an asteroid’s velocity by only a few millimeters per second could still help protect Earth if the asteroid is discovered many years before a possible impact.