DART, a planetary defence mission

DART, a planetary defence mission

In late November, NASA sent a probe to strike the small moon of an asteroid in 2022. This is to check whether we can divert in this way an object which may threaten the Earth. This topic is addressed by our IMAX film, “Asteroid Hunters 3D.”

Asteroid impacts on our planet are not only pretexts for disaster film writers. They are real events, some of which have left traces which are still visible on the Earth’s surface.
While, for the moment, no object has been detected which is on a collision course, the space agencies decided to examine how we could defend our world … just in case!
Update 24 November: take-off successful (an updated article below).


One of the methods being studied is to crash a probe into an asteroid, the trajectory of which would present a collision risk with the Earth. Summed up like that the solution sounds ineffective. Indeed, the mass of a space craft (a few tonnes at the most) will always be ridiculous compared to that of an asteroid capable of causing major destruction (millions of tons). However, the probe’s speed (typically 20,000 km/h or more) will give it a less negligible kinetic energy. The rationale is that a very slight diversion caused to the path of the threatening object will continue to grow over decades, causing a deviation which will save the Earth. This is the principle which NASA will be checking with DART, Double Asteroid Redirection Test. The American agency’s video below explains this aim.

The probe used for DART is a small 560 kg space craft built by the Applied Physics Laboratory (APL) at Johns Hopkins University which is also managing the mission with NASA’s Planetary Defense Coordination Office. This is the agency’s first planetary defence mission.
DART successfully took off from the Vandenberg base on 23 November at 22.31, local time in California (on 24 November at 7.21 am in France) atop a SpaceX Falcon 9 launcher (below, video of the launch).

The probe is now heading towards the 780 m wide asteroid, Didymos, discovered in 1996. But that is not the target. Equipped with independent navigation which will use the onboard camera DRACO (Didymos Recognition and Asteroid Camera for Optical navigation), DART is aiming for the 160 m wide Dimorphos, the asteroid’s moon. The impact will be examined by several observatories on Earth and by an Italian mini satellite (LICIACube) released by DART a few days before.

Principe de la mission DART. La sonde entre en collision avec la lune Dimorphos de l’astéroïde Didymos en 2022 alors que le mini-satellite italien LICIACube observe le tout. Sous l’effet de l’impact, l’orbite d’origine (en blanc) de la petite lune est modifiée (en bleu), ce qui prouvera qu’une telle collision volontaire peut altérer la trajectoire d’un objet céleste. Crédit : NASA/Johns Hopkins APL

Principle of the DART Mission. The probe will collide with the Didymos asteroid’s moon, Dimorphos, in 2022, while the Italian mini satellite LICIACube observes everything.
Under the effect of the impact, the original orbit (in white) of the little moon will be changed (in blue), which will prove that such a deliberate collision can alter the path of a heavenly body. Credit: NASA/Johns Hopkins APL

The Dimorphos collision by DART will take place between 26 September and 2 October 2022. The 560 kg probe will strike the 4.8 million tonnes little moon at a speed of 23,688 km/h. The calculations show that Dimorphos’s orbit around Didymos of almost twelve hours will be reduced by around ten minutes. The main aim of the mission is precisely to check the theoretical models.


The data collected before and after DART’s impact will allow scientists to refine their knowledge about this global defence technique in the event we need to use it. Because the other aspect of the long-term rationale for protecting our planet against a collision with an asteroid is, of course, monitoring the sky. This is already happening with several automatic telescopes which scan the vault of night to catalogue the “wandering rocks” of the Solar System and identify those which pose a threat. The space agencies and scientific institutions are working by following a principle which can be summed up as “find the asteroids before they find us!”

This mobilisation is the subject of the IMAX film “Asteroid Hunters 3D” which is currently showing at Cité de l’espace in Toulouse at the IMAX (trailer below).


This is an international endeavour. Moreover, after the DART mission, the European Space Agency (ESA) will make its contribution. In 2023, Ariane 6 will send the HERA probe to Didymos and Dimorphos which will carry out precise measurements to study the effects of 2022’s impact.

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