The Lucy team, including University of Maryland Professor Jessica Sunshine, detailed this finding in a paper published in Nature on May 29, 2024. This discovery challenges existing theories about the formation of asteroids and celestial bodies, offering new insights into the structure and history of Dinky and Selam.
"There's a lot more complexity in these small bodies than we originally thought," said Sunshine, a co-author of the paper. "With the additional observations taken by the spacecraft, we were able to better analyze features such as Dinkinesh's rotation speed and Selam's orbit pattern. We also have a better understanding of what materials they're possibly made of, bringing us a step closer to learning just how terrestrial bodies are created."
Images from the Lucy spacecraft showed a trough on Dinkinesh where a portion had broken off, a ridge from the structural failure, and the contact binary Selam. The team theorized that Dinky's fast spinning motion caused it to shed debris into orbit, forming Selam, while some fragments created ridges on Dinky.
"One of the things that's critical to understanding how planets like Earth got here is understanding how objects behave when they hit each other, and to understand that we need to understand their strength," said lead scientist Hal Levison of Southwest Research Institute, Boulder, Colorado, principal investigator for the Lucy mission. "Basically, the planets formed when [smaller objects like asteroids] orbiting the Sun ran into each other. Whether objects break apart when they hit or stick together has a lot to do with their strength and internal structure."
The team deduced that Dinky likely has some internal strength, maintaining most of its form.
Sunshine highlighted the potential for comparative studies with similar systems. "I'm personally very excited to compare the Didymos binary system with this one, especially as they appear to share many similarities such as size, general shape and possibly composition despite being in totally different parts of the solar system," explained Sunshine, who was also on NASA's DART research team and helped detail the DART spacecraft's successful deflection of Didymos' small moon called Dimorphos.
"The Didymos binary system is located in a near-Earth environment while the Dinkinesh system is located much farther away from Earth in the main asteroid belt," she added. "They have very different features but we think they may have undergone similar processes to become what we know of them today."
Dinkinesh and its satellite are the first of 11 asteroids Lucy plans to explore over its 12-year mission. After skimming the inner edge of the asteroid belt, Lucy will head back to Earth for a gravity assist in December 2024, then return to observe asteroid Donaldjohanson in April 2025 and the Trojan asteroids in 2027.
"Our ultimate goal is to understand the formation of celestial bodies," Sunshine said. "How do planets form? How was Earth formed? We know that big planets are formed by smaller bodies, so studying these little asteroids lets us see how materials behave and interact on a smaller scale. With Dinky and the other asteroids we're flying by, we're laying the groundwork for understanding how planets are made."
Research Report:Contact Binary Satellite of the Asteroid (152830) Dinkinesh
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