A physical model explaining the origin of the diamond shape of the asteroids Bennu and Ryugu


A team of scientists has used simple concepts from grain physics to explain the strange diamond shapes of two “near Earth” asteroids.

Asteroids are rocky bodies that revolve around the sun. What makes it interesting to scientists is that it consists of leftover material that was not absorbed into the large planets when the solar system formed about 4.6 billion years ago. This allows shedding light on the early days of the solar system and the formation of the planets.

Most asteroids are trapped in the asteroid belt, an area between Jupiter and Mars. This distance from the Earth makes it difficult to study. However, sometimes, an asteroid escapes and approaches Earth, which makes it possible to photograph it up close using an unmanned spacecraft.

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This is what happened to the two “diamond” asteroids, Bennu and Ryugu, which are classified as rubble pile asteroids, which means that they are made up of many smaller pieces of rocky material that are bound together loosely by gravity. And basically, it’s just grains that interact with each other, like the sand on our beaches.

Dr Taban Sabwala, lead author of the paper published in Granular Matter and researcher in the Fluid Mechanics Unit at the Okinawa Institute of Graduate University of Science and Technology (OIST), explained: “But when the asteroids were simulated using these models, they were oblate or asymmetric instead of diamond.”

Until now its distinctive rhomboid shape, with the highest poles and an equator, has been the subject of debate among astronomers. According to a simple granular physics model, scientists observed that both celestial bodies consist of a clump of debris bound together by a relatively weak gravitational force and that they rotate at high speed on their axis.

Granular physicists can predict the shape of the aggregate based on the different forces that act on the particles. Dr. Sabwala, along with Professor Benaki Chakraborty and Professor Troy Scheinbrot of Rutgers University, modeled the evolutionary process of both Beno and Ryugu, using analytical expressions and debris accumulation simulations.

In this way, they noticed that the centrifugal forces generated by the rotation of the celestial bodies are weaker in the regions near the poles, which leads to the rise of the material accumulated there.

Moreover, their calculations indicate that Beno and Ryugu acquired this shape at an early stage of their development, contrary to previous hypotheses that attributed to them the initial spherical shape that would later distort it.

They concluded that the models used so far were missing the irregular particles, which are a key component in forming the shape of the asteroid.

Source: phys.org


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