How asteroids named 'Dinky' and 'Selam' became bound together forever

When NASA’s Lucy spacecraft whizzed past the asteroid known as “Dinky” in November 2023, it wasn’t just a routine flyby. Researchers found that the asteroid was not traversing the cosmos alone; a moon, whimsically named “Selam,” was orbiting Dinky.

But the surprises didn’t stop there. Further data revealed that Selam itself was no ordinary moon but a contact binary — essentially, two tiny moons that had merged into one.

Complexities of asteroid Dinky and its moons

This revelation, detailed by the Lucy team in a recent study, has intrigued astronomers and challenged our existing theories on the formation of celestial bodies.

The team, including University of Maryland‘s Professor Jessica Sunshine, suggests that the internal structure and dynamics of these tiny moons could reshape our understanding of how terrestrial bodies come into existence.

Jessica Sunshine highlighted the complexity uncovered by the spacecraft’s observations. “We’ve seen Dinkinesh’s rotation speed and analyzed Selam’s orbit pattern more closely,” she noted. “This helps us hypothesize about their composition and brings us closer to understanding the creation of terrestrial bodies.”

The story of how Selam came to be is as dramatic as it is fascinating.

Lucy’s images showed that about a quarter of Dinky asteroid had broken off, likely due to its fast spinning motion, which might have been influenced by the uneven reflection of sunlight.

This ejection of rocky debris likely helped form Selam. Meanwhile, other fragments fell back onto Dinky, forming visible ridges on the asteroid’s surface.

Broader implications for planetary science

The study’s lead scientist, Hal Levison from the Southwest Research Institute, emphasized the broader significance of these findings.

Understanding the interaction between colliding celestial objects, like asteroids, is crucial for understanding how planets, including Earth, were formed.

“Whether these objects break apart or coalesce during collisions tells us much about their internal strength and structure,” Levison explained.

Comparison with other celestial bodies

The dual moons of Dinkinesh also invite comparisons with similar systems, such as the Didymos binary system, which is located much closer to Earth.

Despite their distance from each other, these systems may have undergone similar processes.

“I’m personally very excited to compare the two systems,” said Sunshine, who also worked on NASA’s DART mission that successfully altered the trajectory of Didymos’ moon, Dimorphos.

Lucy’s continuing journey through space

Dinkinesh and Selam are just the beginning of Lucy’s cosmic itinerary. The spacecraft is slated to explore a total of 11 asteroids over its 12-year mission.

After its initial observations, Lucy will utilize a gravity assist from Earth to propel it deeper into space, where it will continue its observations, including a planned encounter with the asteroid Donaldjohanson in 2025, and later, the Trojan asteroids in 2027.

“The goal is to peel back the layers of how planets are formed. By studying these smaller celestial bodies, we gather crucial data on the material interactions that might mirror those that formed larger planetary bodies like Earth,” Sunshine concluded.

The journey of Lucy not only enriches our understanding of the universe but also continues to pose intriguing questions about the very processes that may have shaped our own planet.

The findings from Dinkinesh and Selam serve as a testament to the dynamic and ever-evolving nature of space exploration, providing us with insights that could one day answer some of the most fundamental questions about our place in the cosmos.

More on Dinky and asteroid-moon systems

Asteroid-moon systems, like Dinky and Selam, are of great interest to astronomers as they offer crucial insights into the mechanics of celestial interactions.

These systems are often formed through complex processes such as collisions, gravitational captures, and material ejections.

Studying these systems helps scientists understand the dynamics of binary systems and the evolution of the solar system.

Future research can focus on the detailed dynamics of these systems, exploring how moons influence the rotational and orbital characteristics of their parent asteroids.

Advanced missions could utilize high-resolution imaging, spectroscopic analysis, and even landers to study the surface composition and internal structure of both the asteroids and their moons.

Asteroid-moon systems also provide a natural laboratory for studying the effects of the Yarkovsky and YORP (Yarkovsky–O’Keefe–Radzievskii–Paddack) effects, which influence the spin and orbit of small bodies.

Understanding these processes is critical for predicting the long-term behavior of near-Earth objects, potentially improving our ability to mitigate asteroid impact threats.

The full study was published in the journal Nature.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–