Bennu and Ryugu, two diamonds in the sky

Scientists from Okinawa Doctoral College of Science and Technology (Oist) and Rutgers University used simple concepts from physics granular to explain the curious diamond shape of two asteroids near Earth.

These two asteroids, Determining and Ryugu, were explored by a space probe, respectively Osiris-REx and Hayabusa 2, which facilitates their study. These two diamond-shaped asteroids are ” engravings Which means they are made up of many small pieces of rock material that are loosely held together by gravity. These are thus essentially grains that interact with each other, such as sable of our beaches.

Tapan Sabuwala, first author of the article published in Granular Matter and researcher at the Fluid Mechanics Unit of Oist, explains: “ Previous models attributed this diamond shape to the forces caused by the rotation, which caused the displacement of the matter from the poles to theequator. But, when asteroids were simulated using these models, the shape was flattened or asymmetric rather than diamond, so we knew something was wrong. We discovered that these models were missing a key ingredient, the deposit of material. And a simple model of physique granular, normally used for the deposition of grains such as sand or sugar, could predict the observed shape ».

From sandcastles to asteroids

Imagine pouring sand or sugar into a funnel, a cocktail of different strengths will cause it to forms a conical heap. The physicists Granular specialists can predict the shape of the pile based on the different forces acting on the grains. Dr. Sabuwala, alongside Professor Pinaki Chakraborty, who heads the unit, and Professor Troy Shinbrot, of Rutgers University, transferred these ideas to asteroids.

Tapan Sabuwala specifies that, on these asteroids, gravity is oriented differently compared to that felt by a pile of sand on a beach and that it therefore has ” had to take this into account in our model, along with the fact that the rotation of the asteroid also plays an important role ».

So instead of the conical shape seen in the accumulation of grains on Earth, the forces at work on the asteroids produced diamond shapes. The centrifugal force, caused by the rotation, decreased near the poles of the asteroids, causing matter to accumulate there and producing their distinctive shape. Another important distinction of this model (compared to previous ones) is that it suggests that these “piles of engravings Didn’t start out as a sphere that warped into a diamond shape. On the contrary, the accumulation of debris led to this diamond shape very early in the formation of the asteroid, and any subsequent remodeling was minimal. Additionally, the idea that these diamond shapes were produced during the early stages of the asteroid’s formation, although at odds with previous models, is consistent with recent observations.

The researchers then showed the accuracy of this model through simulations and found that the simulated asteroids acquired this distinctive diamond shape, bolstering their theory.