What was discovered after the DART probe hit the asteroid Dimorphos?
In September 2022, the DART probe sent by NASA collided head-on with an asteroid to deflect it from its trajectory.
The exercise aimed to evaluate the feasibility of this defense strategy in the event that an astronomical object should be headed for Earth. Keep in mind that this was not the case with Dimorphos, the small target asteroid. Orbiting another larger asteroid called Didymos, this body, almost 170 m in diameter, does not threaten our planet in any way.
The scientists are now analyzing the data collected and taking stock of the mission in a series of five articles published in Nature.
Here’s what emerges from their observations.
Reduced speed of Dimorphos
Scientists observed that the impact of DART on the asteroid Dimorphos resulted in a decrease in its orbital velocity (by 2.70 ± 0.10 mm s-1) around the asteroid Didymos. They found that ejecting material from the asteroid also helped slow its speed. According to the paper’s conclusions, “The successful impact of the DART spacecraft on Dimorphos and the resulting change in orbit demonstrates that kinetic impactor technology is a viable technique to potentially defend Earth if necessary.”
Slow Orbital Race
Dimorphos’ orbital period around Didymos was expected to slow by about 7 minutes after the DART collision. On September 26, 2022, when the spacecraft struck the asteroid, a 33-minute decrease in this “rotation” was observed instead. According to calculations by the international team, Dimorphos now needs 11 h 37 min to completely orbit Didymos.
Impact of the DART spacecraft on Dimorphos. Image: NASA/Johns Hopkins APL
Aim at a small asteroid
In a third article, the researchers recall that we knew very little about the small asteroid Dimorphos. Despite these limitations, the DART spacecraft managed to calculate its trajectory in order to autonomously target and crash at a specific location on the asteroid. “This suggests that a reconnaissance mission is not a prerequisite for intercepting an asteroid,” they conclude.
Participatory science in action
We have been able to learn more about sputum thanks to observations made with telescopes (eVscope) by citizens located on Reunion Island and Kenya, among others. They recorded that the luminosity of the event was at its maximum during the collision and returned to normal after about 23 days. They also estimated that the mass of debris thrown around the asteroid is about 0.3 to 0.5% of the mass of Dimorphos.
Hubble witnessing the impact
The Hubble telescope’s eye was trained on the collision between the DART and the asteroid. This event, detailed in the latest Nature article, was a unique opportunity for astrophysicists to observe the birth of an asteroid tail. Early on, Hubble images show the diffusely scattered debris and clumps near fellow asteroid Didymos. After a period of 3 to 10 hours, the debris, forming a cone cloud, extended up to 500 km from the impact site. The images also showed the formation of a second asteroid tail starting on day 5 after the collision. However, scientists don’t know what caused it, and it was no longer visible after 18 days. According to the observations collected by the DART mission, one could better estimate the age of an asteroid tail by examining the size of the particles that make it up.
The story doesn’t end there: the Hera space mission, planned for 2024, will examine the site of the collision in more detail. We should therefore learn more about “the exact mass of Dimorphos, its composition and internal structure – as well as the size and shape of the crater left by DART”. »