Most small asteroids are just piles of rubble in space, held together by gravity and weak molecular forces. Even the slight touch of sunlight can cause them to break up. Now we know exactly how different-shaped asteroids crumble, which might help us if one ever heads straight for Earth.
Photons carry a tiny amount of momentum, so when sunlight hits an asteroid it can send the space rock spinning, in what is known as the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect.
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“The magnitude of forces acting on these asteroids is like the weight of three grapes sitting on a mountain,” says Masatoshi Hirabayashi at Auburn University in Alabama. “They are really negligible in the short term, but if you wait a couple million years, these three-grape forces can be significant.”
Hirabayashi and Daniel Scheeres at the University of Colorado used simulations to examine how asteroids of various shapes fall apart when the YORP effect makes them spin too fast.
They looked at 24 asteroids, all smaller than 40 kilometres across, and split them into four groups: spheroids, elongated objects, contact binaries – “rubber ducky” shapes like comet 67P – and others.
They found that the spherical asteroids tended to collapse from the centre, causing them to break into lots of smaller pieces. The elongated ones snapped in the middle or at their narrowest points, and the binaries broke apart at the narrow connection point – the duck’s neck, in other words. The other bodies were more complicated, falling apart in the middle and the edges simultaneously.
The research could prove useful if Earth is ever in danger of a major asteroid strike, says Scheeres. “If we understand how asteroids break apart, then we could potentially leverage that information.” Imparting a little bit of spin to break a killer asteroid could be much easier than smashing it up directly, Harabayashi says.
It could also help us figure out how to mine asteroids for useful resources like iron or water. “By looking at the current shape, we can try to figure out what kind of shape the asteroid had in the past, which can help us understand the origin of the asteroid and its internal structure,” Harabayashi says. “If you know the inside of the asteroid, you will be able to understand what locations will be the best for mining.”
Icarus
