Weak forces hold rubble-pile asteroids together

There are millions of these lurking in Earth’s back yard.

NASA

Millions of asteroids of all shapes and sizes are littered throughout the inner Solar System. In the past three decades, scientists have spotted as many as 500,000, but plenty more remain unseen. And many of them have a “rubble pile” internal structure, which is rather unusual compared to other bodies in the Solar System.

Rubble-pile asteroids are exactly what they sound like: a grouping of different sized rocks brought together under the influence of gravity. Its constituent pieces could be anything from large boulders tens of meters in size to dust particles smaller than a thousandth of a meter in diameter.

Until now, it was assumed that the main forces that hold all these pieces together were gravity and friction. But a rubble-pile asteroid named (29075) 1950 DA, with a diameter of 1.3km, is an exceptional case, one where some other force must be involved.