On September 26, 2022, NASA's Double Asteroid Redirection Test (DART) mission made headlines when it collided with the moon of an asteroid called Didymos. The mission's primary objectives were to prove that it was possible to target an asteroid in a high-speed encounter and demonstrate that the target's orbit could be changed, both of which were achieved. In a new study, astronomers reported that DART was a "viable technique to potentially defend Earth if necessary." In this article, we will explore DART's epic asteroid crash and what NASA learned five months later.
DART Mission's Goals and Success
DART's primary goal was to demonstrate that a "kinetic impactor" like itself could target and change the orbit of an asteroid. The success of this mission indicates that this technique could be used to defend Earth from a dangerous space rock in the future. The spacecraft, which collided with a moon called Dimorphos, was traveling at around 15,000 miles per hour. Two new studies on the mission were published in the journal Nature, which provided additional findings from the mission.
DART's Final Moments
DART's final moments have been reconstructed using data the probe sent home. A month before impact, the probe started sending pictures every five hours, which were processed by a ground optical navigation team. About four hours before impact, the researchers handed over control to DART and allowed it to navigate itself using its autonomous SMART Nav system. The mission team kept DART moving towards Didymos until it could detect Dimorphos, which it did 73 minutes before impact. DART clicked one image every second for about 2.5 minutes before crashing, including a picture of its impact site.
Dimorphos' Puzzling Twin Tails
One of the new studies revealed that Dimorphos has twin tails, which is puzzling to astronomers. The spacecraft's collision with Dimorphos caused a crater, and Hera, the European Space Agency's spacecraft, will study this system in more detail. Hera is expected to launch in October 2024 and reach Didymos two years later. Carolyn Ernst, a planetary scientist at The Johns Hopkins University Applied Physics Laboratory (APL) and a co-author of one of the studies, said, "This situation is rare for planetary exploration, and is very exciting!"
How DART's Impact Changed Dimorphos' Orbit
When DART collided with Dimorphos, it hit the asteroid's leading hemisphere, the one facing forward as the rock travels around the sun. The impact shortened Dimorphos' orbit by 33 minutes, which was a success for the mission. The asteroid previously orbited Didymos every 11 hours and 55 minutes.
Modeling the Asteroid's Shape
Using DART's data, researchers modeled Dimorphos' shape using a technique called stereophotoclinometry. The modeling revealed that Dimorphos is an oblate spheroid, like a rugby ball, with a diameter of 580 feet (177 m). Ernst said that her team is working on new models and experiments to better understand what happened during DART's impact and how the event changed the asteroid's orbit and spin.