Planetary SecurityDisrupting Asteroids to Protect the Earth

If an asteroid is determined to be on an Earth-impacting trajectory, scientists typically want to stage a deflection, where the asteroid is gently nudged by a relatively small change in velocity, while keeping the bulk of the asteroid together.

A kinetic impactor or a standoff nuclear explosion can achieve a deflection. However, if the warning time is too short to stage a successful deflection, another option is to couple a lot of energy to the asteroid and break it up into many well-dispersed fragments. This approach is called disruption and it is often what people think of when they picture planetary defense. While scientists would prefer to have more warning time, they need to be prepared for any possible scenario, as many near-Earth asteroids remain undiscovered.

Now, new research takes a closer look into at how different asteroid orbits and different fragment velocity distributions affect the fate of the fragments, using initial conditions from a hydrodynamics calculation, where a 1-Megaton-yield device was deployed a few meters off the surface of a Bennu-shaped, 100-meter diameter asteroid (1/5 the scale of Bennu, a near-Earth asteroid discovered in 1999). See the video.

The work is featured in a paper published in Acta Astronautica with lead author Patrick King, a former Lawrence Livermore National Laboratory Graduate Scholar Program fellow who worked with LLNL’s Planetary Defense group on this research as part of his Ph.D. thesis. King currently works at the Johns Hopkins University Applied Physics Laboratory (JHUAPL) as a physicist in the Space Exploration Sector. Co-authors of the paper include Megan Bruck Syal, David Dearborn, Robert Managan, Michael Owen and Cody Raskin.

The results highlighted in the paper are reassuring: for all five asteroid orbits considered, carrying out the disruption just two months before the Earth impact date was able to reduce the fraction of impacting mass by factor of 1,000 or more (99.9 percent of the mass misses Earth). For a larger asteroid, the dispersal would be less robust, but even dispersal velocities reduced by an order of magnitude would result in 99 percent of the mass missing Earth, if disruption is staged at least six months ahead of the impact date.