Out of This World – The Mystery of Watermelon-Shaped Asteroids
Asteroids come in various shapes and sizes, but some, like Dimorphos, have captured scientific attention due to their peculiar “watermelon-like” shape. Recent research has begun to shed light on why certain asteroids exhibit this unusual form, providing insights into the complex processes that shape these celestial bodies.
An image of the 530-foot diameter asteroid Dimorphos taken by the DART mission. It orbits a larger asteroid called Didymos. (Credit: NASA)Dimorphos, a small asteroid with a length of about 160 meters, is one of the most prominent examples of this oddly elongated shape. Traditionally, asteroids are believed to be roughly spherical or irregularly shaped due to the collisions and gravitational forces they encounter over millions of years. However, the elongated, watermelon-like form of Dimorphos and others like it suggests a different story.
Scientists propose that these shapes could be the result of a process known as “YORP-induced spin-up.” The Yarkovsky-O’Keefe-Radzievskii-Paddack (YORP) effect occurs when an asteroid absorbs sunlight and re-emits it as heat, creating a tiny but consistent force on the asteroid. Over long periods, this force can cause the asteroid to spin faster. As the rotation speeds up, the centrifugal force increases, potentially reshaping the asteroid into an elongated form, resembling a watermelon.
Furthermore, this spin-up can lead to the asteroid’s surface material migrating toward the equator, further contributing to the distinctive shape. In some cases, this process might even cause the asteroid to break apart, forming binary systems like Didymos and Dimorphos, where the smaller body orbits the larger one.
Understanding the shape of asteroids like Dimorphos is not just a matter of academic interest; it also has practical implications for planetary defense. Knowing how these bodies form and evolve can help scientists predict their behavior and better design missions to deflect potential Earth-threatening asteroids.
As research continues, the strange shapes of asteroids like Dimorphos may offer more clues about the dynamic and ever-changing nature of our solar system.
