The DART Mission: A Test to Change an Object’s Orbit

By Betty Robinson,

Over 4.5 billion years ago, the solar system was filled with billions of pieces of rocky debris. Over time, this debris coalesced into the solar system components we know today: the planets, moons, asteroids, comets, and other objects.

Today, there is still debris in space. While the pieces of rocky debris are nowhere near as numerous as they were billions of years ago, there are still asteroids and other rocky bits that approach Earth. These objects are called near-Earth objects, and the larger ones (140 metres in diameter) are definitely of concern. They are fast-moving, and when they hit another object, they could cause much harm. One such event 60 million years ago wiped out the dinosaurs! Scientists are looking for ways to protect Earth from these near-Earth objects.

There are four main ways to protect Earth from near-Earth objects under study at the moment:

      1. For a predicted small impact, clear the area of people.
      2. For predicted larger impacts, try to gradually change the object’s orbit with small nudges so it doesn’t hit Earth at all.
      3. Try to quickly change the object’s orbit by giving it a huge nudge so it doesn’t hit Earth at all.
      4. More or less blow it up.

A NASA mission is underway right now to test the nudging option. The mission is called DART, or the Double Asteroid Redirection Test. Launched on November 24, 2021, DART is the first demonstration of trying to change the orbit of a celestial object. DART is headed for an asteroid called Didymos. This asteroid has a moon called Dimorphos, about 1.2 kilometres away.

Didymos is Greek for “twin,” and Dimorphos is Greek for “two forms.” This refers to the change in the orbit of Dimorphos before and after DART collides with it.

Dimorphos is about 160 metres in diameter. For scale, the height of the Skylon Tower in Niagara Falls, Ontario, is 158 metres. And the diameter of Didymos is about 780 metres, about the height of five stacked Skylon Towers.

DART will crash into Dimorphos in the fall of 2022. A camera onboard DART will photograph the collision, as will a tiny satellite, or CubeSat. DART will release the CubeSat 10 days before the impact so that it will be trailing DART and can watch the whole thing. The collision is predicted to increase the speed of Dimorphos around Didymos, which will shorten the time it takes to orbit Didymos by up to 10 minutes. So the orbit will change. And it is possible that the energy from the collision could make Dimorphos unstable and start to tumble. Scientists haven’t yet determined the precise shape and composition of Dimorphos, but it could be a pile of rubble, like Didymos may be.


Artist’s conception of DART and the CubeSat approaching Dimorphos. DART will hit Dimorphos head-on at a speed of about 23,760 kilometres per hour. Credit: NASA/Johns Hopkins Applied Physics Lab (Note: The drawing is not to scale. DART is about the size of a small car.)

As a follow-up, in 2024 the European Space Agency (ESA) will launch a spacecraft called Hera. (Hera is the Greek goddess of marriage.) Hera will study the Didymos–Dimorphos system to see the effects of the DART collision. Hera’s mission will also include CubeSats, which will do the close-up observations of Dimorphos.

The ESA and NASA missions reinforce the need for, and importance of, international co-operation to help protect our planet.

 The results of this demonstration will show us if we can, in fact, divert an asteroid that is on a collision course with Earth and do what the dinosaurs could not: avert a species-ending disaster.