Our understanding of the solar system has taken a fascinating turn. In a groundbreaking discovery, NASA’s Lucy mission, in November 2023, revealed that a small asteroid, affectionately known as ‘Dinky’ (officially Dinkinesh), was not alone. A tiny moon, named ‘Selam,’ was discovered in its orbit. But the real surprise came when scientists on the Lucy team delved deeper into the data: Selam was not a single moon, but two tiny moons fused together, forming a rare celestial wonder known as a contact binary.
This discovery marks the first time a contact binary has ever been observed orbiting an asteroid. Contact binaries are fascinating objects – essentially two celestial bodies gently touching like two billiard balls nudged together. They’re much more common in star systems, where two stars can gravitationally lock and share a standard gas envelope. But finding them in the realm of asteroids, which are typically much smaller and less massive, throws a curveball at our understanding of how these systems form.
The prevailing theory suggests that Selam’s two moonlets likely originated from Dinky. As the asteroid spun rapidly in its early formation stages, some loosely bound material may have been flung off by centrifugal force. These fragments remained in Dinky’s gravitational grip, eventually merging into two mini-moons orbiting their parent asteroid. The big question remains: how did these two moonlets then become one?
Picture a slow, graceful waltz in the vastness of space. Over countless orbits, the two moons of Selam, drawn together by their mutual gravity, began a dance of convergence. As their orbits intertwined, the pull of their gravity grew stronger until it became irresistible. In a cosmic embrace, the two moons merged, forming the single, peculiarly shaped moon we see today. The exact details of this celestial merger remain a mystery, but further exploration of Selam may provide valuable insights.
This discovery isn’t just a quirky oddity; it sheds light on the complex processes that govern the birth and evolution of celestial bodies. Studying contact binaries like Selam can help us understand how moons form around asteroids and potentially even planets. It also raises questions about the prevalence of these systems. Could more “double moons” be out there, waiting to be discovered?
The Lucy mission’s encounter with Dinky and Selam reminds us that space is full of surprises. By exploring these unique celestial objects, we gain a deeper appreciation for the diversity and dynamism of our solar system and even unlock secrets about the formation of our planet and its moon. The discovery of the first contact binary around an asteroid is a testament to the power of space exploration and the wonders still waiting to be revealed.