Hidden beneath the idea of the asteroids being plain space rocks is a more complex issue. Recent studies have shown that certain asteroids may possess moons having strange shapes like watermelons, which defy theories on how asteroids form.
For many years, astronomers wondered about the irregular geometries of minor rocky bodies like Dimorphos and Selam. In a new study, researchers bring to light some reasons for their bizarre appearances and argue that such atypical “moonlets” might be far more common than previously thought.
Understanding Binary Asteroids and Their Moonlets
In our solar system, there are several binary pairs resembling miniature Earth-moon systems. These include Didymos-Dimorphos which is central to NASA’s 2022 Double Asteroid Redirection Test (DART) mission.
According to studies, such binary systems occur when a fast spinning ‘parent’ asteroid made up of loosely aggregated rocks sloughs off matter that coalesces into a smaller satellite or ‘moonlet’.
Normally, these moonlets resemble prolate ellipsoids or upright blunt-end footballs. However, some moonlets had different forms than this, including ones such as Dimorphos before DART’s impact.
In shape, it was an ‘oblate spheroid’ – flattened at the poles but elongated at the equator, similar to that of a watermelon. On the other hand, Selam has two touching rocky globes forming its structure; she is actually an attendant of asteroid Dinkinesh.
These oddities caught the attention of some astronomers, including a graduate student from University of Bern named John Wimarsson, who is the lead author of the study. “Traditional models have no direct solutions to these asteroid satellites,” Wimarsson said.
In order to make clearer in regard to this problem, Wimarsson and his group of scientists from Europe and America came up with two computer models. The first one was aimed at simulating how parent asteroids change shape when they spin off material.
The other one assumed a disk shaped like a doughnut around the debris made by the parent that followed their motion and collision. They also looked into two different kinds of parent asteroids, akin to Ryugu and Didymos.
A moonlet’s shape can be influenced majorly by two things: gravity from its host asteroid, and collisions within its debris disk, all as revealed in a research paper printed in science journal Icarus.
Moreover, additional parameters are important in determining which factor will dominate over the other. For example, faster spinning denser asteroids such as Didymos result in wider debris disks that push moonlets further away from them. At a certain point equal to Roche limit, where gravitational forces equals to internal forces acting on the moonlet, often leads to prolate shapes.
Conversely, moonlets forming beyond the Roche limit tend to be oblate, as they are less influenced by the parent's gravity. Collisions with other debris lead to more uniform growth. If too close, moonlets may be torn apart, losing their prolate forms and more likely becoming oblate spheroids after subsequent collisions.
The collision angle between precursor moonlets also affects the final shape. Side-to-side collisions align along short axes, creating oblate shapes. In contrast, edge-to-edge collisions along longer axes result in bilobate objects, similar to Selam.
The Implications of Unusual Moonlet Shapes
The discovery of these unusually shaped moonlets challenges our previous understanding of asteroid formation. Traditional models have struggled to explain the existence of such shapes, leading to a reevaluation of the processes that govern the evolution of binary asteroid systems.
This research suggests that oblate and bilobate moonlets may be more common than previously believed. However, due to technological limitations, these shapes are often overlooked, leading to a skewed perception of their prevalence in our solar system. As technology advances, we may discover that these peculiar shapes are not the exception but the rule.
The findings from this study open up new avenues for research and exploration. Understanding the formation and evolution of these moonlets could provide valuable insights into the early history of our solar system. As we continue to explore these distant celestial bodies, we may uncover even more complex and intriguing shapes, further deepening our understanding of the cosmos.