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Landing on asteroids could cause a zero-gravity avalanche

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Asteroid credit NASA JPL
Asteroid credit NASA JPL

Asteroids may not be as stable as scientists thought. A recent experiment shows that the force from a landing spacecraft might easily cause an avalanche or something resembling an extraterrestrial mudslide, as a result of shifts in the dust on the asteroid's granular surface.

The research is especially relevant after recent proposals for private-sector asteroid mining

Researchers compare the force chains to a stack of oranges at the supermarket. Some oranges bear weight while others come away easily, and a small shift in the stack can redistribute the force, moving the weight to different oranges and causing some to topple off the pile. Asteroids work much the same way, with only weak gravity holding together layers of loose rock and dust called regolith. The shock of a spacecraft landing could rearrange the dust in unpredictable ways — and because the gravity is so much weaker than on Earth, the results could be much less stable than the stack of oranges.

The research is especially relevant after recent proposals for private-sector asteroid mining and NASA's plan to place an asteroid in orbit for a potential manned visit. According to the report, these projects would be dealing with an unstable environment, prone to unpredictable ground shifts in response to the slightest movement. "A lander touching down on the surface on one side of a small, rubble-pile asteroid could perhaps cause an avalanche on the other side, by long-range transmission of forces through chains," said Dr. Naomi Murdoch, the lead researcher on the project, speaking to the Royal Astronomical Society where she presented the results this Thursday.

To test this hypothesis, researchers used a drum of glass beads to simulate the regolith, and packed it into an Airbus A300, which flew in parabolic patterns to simulate zero-gravity. By tracking the movement of the beads, researchers were able to observe how force chains formed and were disrupted, modeling the same behavior on the surface of an asteroid. The result is a surprisingly complex picture of the physics of dust in space, constantly reorganizing and reshaping itself. One of the most useful takeaways is that the angle of approach is particular important for spacecraft, so would-be asteroid miners will have to plot their landing trajectories particularly carefully.