On September 26, after a nine-month journey through the solar system, NASA’s Double Asteroid Redirection Test (DART) mission struck an asteroid named Dimorphos.
NASA scored a direct hit when DART – about the size of a vending machine – hit Dimorphos within 10% of the 160-meter-tall asteroid’s center. The impact changed Dimorphos’ orbit around its larger companion asteroid Didymos by more than 30 minutes, far exceeding the original target.
This is the first time humans have intentionally altered the motion of a significant object in the solar system. The test shows that it is plausible to use similar future missions to protect Earth from asteroid impacts if needed.
An amazing achievement
The successful mission is an amazing feat of science and technology. During the final stages of the pre-impact approach, DART autonomously navigated to the impact site, processed imagery onboard the spacecraft, and adjusted its trajectory without human intervention.
Many telescopes on Earth and an Italian spacecraft tagged with DART were able to get amazing images of the impact. Even small telescopes captured spectacular views, showing an enormous plume of debris from the impact that developed into a trail that now follows the asteroid through space.
The DART mission was the first test of planetary defense — using a spacecraft to alter the trajectory of an asteroid.
In the future, such a technique could protect Earth from an asteroid impact if we spot an asteroid on a collision course with us. A collision could be avoided by changing the direction of a far-earth asteroid.
How was DART so successful?
Dimorphos was chosen as a target for DART because it is part of a dual asteroid system – it orbits a larger, 780 meter high asteroid called Didymos. Before the impact, this orbit was very regular and could be measured with large telescopes from Earth. Measurements showed that the orbital period was about 11 hours and 55 minutes.
The goal of the DART mission was to show that Dimorphos’ orbit would be altered by the impact, which occurred 11 million kilometers from Earth with the spacecraft traveling at a speed of 25,000 kilometers per hour.
Telescopes on Earth measured the orbit before and after the impact. The minimum change in orbit to account for mission success was 73 seconds.
The data is in and DART changed Dimorphos’ orbit by a whopping 32 minutes (plus or minus 2 minutes).
The change is large, partly because of the resulting plume of debris. The act of throwing all that debris off the asteroid created recoil, like the recoil of a gun; The bullet is fired in one direction and the gun recoils in the opposite direction. The same goes for the debris plume and the asteroid.
Good news for planetary defenses
DART was therefore a great success in every respect. DART hit the mark, showing that missions like this can alter asteroid trajectories. The idea has been around for a long time and has inspired many asteroid films. Now technology and science have caught up.
In the future, if an asteroid is on a collision path with Earth and we have enough warnings, a next-generation mission based on the DART experience could well save Earth and humanity from significant casualties.
DART cost approximately $324 million, and as of this writing, it looks like money well spent.
As more impact data is analyzed, planetary defense techniques can be refined. We will also learn a lot about asteroids from the data collected. A European mission is scheduled to go to the Didymos/Dimorphos system and take a close look at the impact crater, which will provide even more detailed information.
Steven Tingay, John Curtin Distinguished Professor (Radio Astronomy), Curtin University
This article was republished by The Conversation under a Creative Commons license. Read the original article.
also read | DART: NASA’s crash succeeded in shifting an asteroid’s orbit
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