Led by Harrison Agrusa of the University of Maryland, the researchers calculated how the momentum of the impact would change the roll, pitch, and yaw of the asteroid, and simulated that DART might change the spin or spin of Dimorphos. The degree of rotation. The results can be dramatic. “It may start to roll over and enter a state of chaos,” Agrusa said. “This is really a big surprise.”
Unexpected rotation brings some interesting challenges. This will increase the difficulty of landing on asteroids, and ESA hopes to use two small spacecraft in its Hera mission to try. It may also complicate future attempts to deflect Earth asteroids, because any rotation will affect the asteroid’s path in space.
When DART hits Dimorphos, its impact energy will be comparable to the explosion of 3 tons of TNT, sending out thousands of fragments Pouring into spaceStatler described it as a golf cart driving at 15,000 miles per hour crashing into the side of a football field. According to Agrusa and his team, the force of the impact will not immediately cause any changes to the rotation of Dimorphos, but things will start to change within a few days.
Soon, Dimorphos will begin to shake slightly. As the momentum generated by the impact makes the Dimorphos spin out of balance, this swing will become larger and larger, and there is no friction in the vacuum of space to slow its speed. Dimorphos may start to rotate in one way and another. It may start to rotate along its long axis, like a rotisserie. For observers on Didymos looking up at the sky, this seemingly stable satellite will take on a new form—starting to swing back and forth crazily, and its previously hidden side now comes into view.
In a few weeks, Dimorphos can spin so much that it enters a chaotic tumbling state in which it rotates uncontrollably around its axis. Agrusa said that in more extreme situations, Didymos’s tidal lock could break completely, and Dimorphos could begin to “turn upside down.”
What happens depends on a few things. The shape of Dimorphos will play an important role-if it is more slender than spherical, it will rotate more chaotically. Radar observations so far indicate that it is elongated, but we won’t know it until a few hours before DART hits, when it first sees its small target.