NASA is going to crash a spaceship on an asteroid. Things could get pretty chaotic.

Led by Harrison Agrusa of the University of Maryland, the researchers modeled how much DART could alter the spin or spin of Dimorphos by calculating how the momentum of impact will alter the roll, pitch and yaw of the asteroid. The results could be dramatic. “It could start to tumble and go into a chaotic state,” says Agrusa. “It was really a big surprise.”

The unexpected rotation poses interesting challenges. This will add to the difficulty of landing on the asteroid, which ESA hopes to attempt with two small spacecraft during its Hera mission. It could also complicate future attempts to deflect an Earth asteroid, as any rotation can affect an asteroid’s trajectory in space.

When DART collides with Dimorphos, the energy of the impact will be comparable to the explosion of three tons of TNT, sending out thousands of debris throw up in space. Statler describes it as a golf cart traveling at 15,000 miles an hour crashing into the side of a football stadium. The force of the impact won’t cause any immediate change in Dimorphos’ rotation, but within days things will start to change, according to Agrusa and her team.

Soon, Dimorphos will start to wobble very slightly. This oscillation will grow and grow as the momentum of impact unbalances the rotation of Dimorphos, with no friction in the vacuum of space to slow it down. Dimorphos can start spinning either way. It can start to rotate along its long axis, like a rotisserie. To an observer of Didymos looking up at the sky, this seemingly calm satellite will take on a new form: it will begin to rock wildly back and forth, its previously hidden sides now appearing.

Within a few weeks, Dimorphos could spin so much that he would enter a chaotic tumbling state where he spun uncontrollably around his axes. In more extreme scenarios, the tidal lock with Didymos could break completely and Dimorphos could start to tip “head over heels,” says Agrusa.

What exactly happens will depend on several things. The shape of Dimorphos will play an important role – if it is more elongated than spherical, it will spin more chaotically. Radar observations so far suggest he’s lying down, but we’ll only know a few hours before DART hits, when he gets his first views of his small target.

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