Shatter asteroids with sunlight

  Most small asteroids (or comets) are nothing more than a pile of rubble in space, held together by gravity and weak intermolecular forces. Even the slight “touch” of sunlight can disperse them.
   We know that photons are like flying balls, carrying tiny momentum, so when the sun shines on the asteroid, it can make the asteroid rotate. This is the so-called YORP effect.
   The force of sunlight on these asteroids is like the weight of three grapes on a mountain. In the short term, the effect is negligible, but because this force persists, if you wait for millions of years, It may be very important.
   Recently, two scientists in the United States used simulations to observe how asteroids of various shapes will disintegrate if the YORP effect causes the asteroid to rotate too fast.
   They simulated 24 asteroids with a diameter of less than 40 kilometers (they all have real objects in space) and divided them into four groups: spherical, elongated, dumbbell, and other shapes.
   When rotating too fast, spherical asteroids often collapse from the center, causing them to split into many fragments. The elongated asteroid breaks in the middle or at the thinnest point. The dumbbell-shaped asteroid breaks at a narrow junction. Other shapes of asteroids are more complicated, and some break at the center and at the edge at the same time.
   This research helps protect the Earth from asteroid impact in the future. When an asteroid comes straight to the earth, maybe we apply a little force to make it spin up and break up during the rotation, which may be much easier than breaking it up directly.