The destruction of late small celestial asteroids can protect the Earth


Spheral’s hydraulic simulation that provided the basis for the analysis: 1 megaton at a standoff distance of a few meters from an asteroid (Bennu shape) 100 meters in diameter. The color indicates speed. The legend is cm / us, which corresponds to 10 km / s.Credits: Lawrence Livermore National Laboratory

When an asteroid is determined to be in an orbit that affects the Earth, scientists usually want to stage a deflection in which the asteroid is gently moved by relatively small velocity changes, while keeping most of the asteroid together. think.

A dynamic impactor or standoff nuclear explosion can achieve a deflection. However, if the warning time is too short for a successful deflection, another option is to combine a lot of energy into the asteroid and divide it into many well-dispersed asteroids. Fragment.. This approach is called turmoil and is often thought of by people when imagining planetary defense. Scientists want to have more warning times, but many near-Earth asteroids remain undiscovered, so we need to be prepared for every possible scenario.

Now, in a new study, different asteroid orbits and different fragment velocity distributions are destined for fragments, using the initial conditions of hydrodynamic calculations where a 1-megaton yield device is located a few meters away from the surface. We are investigating how it affects us. Bennu-type asteroid with a diameter of 100 meters (1/5 scale of Bennu, a near-Earth asteroid discovered in 1999).

This work, Acta Astronautica With Patrick King, a former Lawrence Livermore National Institute Graduate Scholarship Program Fellow who collaborated with LLNL’s Planet Defense Group on this study as part of his PhD. paper. King is currently working as a physicist in the space exploration sector at the Johns Hopkins University Applied Physics Laboratory (JHUAPL). Co-authors of this treatise include Megan Bruck Syal, David Dearborn, Robert Managan, Michael Owen, and Cody Raskin.

The results emphasized in the treatise are encouraging. By performing destruction of all five considered asteroid orbits just two months before the Earth’s collision date, the proportion of colliding mass can be reduced by more than one-thousandth (99.9% of mass misses). I did. Earth). For larger asteroids, the dispersion is not very robust, but even if the dispersion velocity is reduced by an order of magnitude, 99% of its mass will be lost from Earth if it is destroyed at least 6 months before the collision date.

“One of the challenges in assessing confusion is the need to model all fragment trajectories, which is generally much more complicated than modeling simple deflections,” King said. Says. “Still, if you want to assess confusion as a possible strategy, you need to tackle these challenges.”

King said the main finding of this work was that nuclear destruction was a very effective defense of last resort. “We focused on’late’studies confusion“It means that the colliding object is disassembled just before it collides,” he said.

Kinetic impactors have many advantages. For one, this technique is well known and has been tested in real-world missions such as DART missions, and if you have enough time, you can handle a variety of possible threats. However, due to some limitations, it is important to have multiple options for dealing with the threat, including some ways that you can handle very short warning times in the event of a real emergency. ..

Owen said the treatise is very important for understanding the consequences and requirements for destroying dangerous asteroids approaching Earth. Owen is called Spheral, which is used to model the nuclear destruction of the original asteroid, according to the detailed physics of impacting and destroying the original rock asteroid and capturing the properties of the resulting fragments. I created the software. From there, the team used Spheral to track the evolution of gravity in the fragment cloud, explaining the mutual effects of fragments and the effects of gravity on the sun and planets.

“If you discover that a dangerous object destined to hit the Earth is too slow to bypass safely, the best remaining option is to completely disassemble it and the resulting debris will mostly miss the Earth. That would be the case, “he said. “But this is a complex orbital problem. When you shatter an asteroid, each resulting cloud of debris follows its own path around the Sun and interacts with each other by gravity. Curved stream of fragments around the path of asteroid It was on. How fast those debris spreads (together with the time it takes for the clouds to cross the Earth’s path) indicates how many will hit the Earth. “

Bruck Syal said the work addresses the key goals defined in the White House OSTP’s Near-Earth Object (NEO) Preparatory Strategy and Action Plan. It’s about improving NEO modeling, forecasting, and information integration.

“Our group continues to improve our nuclear deflection and rupture modeling approach, including ongoing improvements in X-ray energy deposition modeling that sets the initial blow-off and impact conditions for the nuclear rupture problem,” she said. Said. “This latest treatise is an important step in demonstrating how to use the latest multiphysics tools to simulate this problem with multiple relevant physical regimes and timescales.”

Different neutron energies enhance asteroid deflection

For more information:
Patrick K. King and others, late-time small body destruction for planetary defense, Acta Astronautica (2021). DOI: 10.1016 / j.actaastro.2021.07.034

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