Led by Harrison Agrusa of the University of Maryland, the researchers modeled how the speed of impact could alter the spin or rotation of the dimorphs by calculating how the asteroid’s roll, pitch, and yaw would change. The results can be dramatic. “He can start messing up and get into a chaotic situation,” Agrusa says. “This was really a big surprise.”
Unexpected spinning poses some interesting challenges. It will increase the difficulty of landing on the asteroid, which ESA hopes to try with two small spacecraft on its Hera mission. It could also make future attempts to complicate asteroids on Earth, as any orbit could affect the asteroid’s path through space.
When DART slamms into deformos, the energy of the impact will be comparable to a three-ton TNT explosion, sending thousands of pieces of debris into space. Stetler describes it as a golf cart that rushes to the side of a football stadium at a speed of 15,000 miles per hour. According to Agrusa and his team, the force of impact will not immediately change the spin of Demorphos, but things will start to change in a few days.
Soon, Dimorphos will begin to tremble very slightly. This tremor will increase and increase as the velocity from the impact throws the rotation of the dimorphous out of balance, to slow it down without any friction in the vacuum of space. Dimorphos can start moving in one way and another. It can start rotating along its long axis like a rotisserie. For the observer in the sky at Didimos, this seemingly silent satellite will assume a new form – swinging wildly back and forth, its previously hidden sides now coming into view.
Within weeks, Dimorphos can spin so much that it enters a chaotic tumbling state where it rotates uncontrollably around its axis. In more extreme scenarios the tidal lock with Didimos could be completely broken and Demorphos could start turning “head over heels”, Agrusa says.
Exactly what will happen will depend on a few things. The shape of the dimorphous will play an important part – if it is more elongated rather than round, it will rotate more chaotically. Radar observations so far indicate that it is extensive, but we will not know until a few hours after hitting the dart, when it gets the first views of its small target.