There is more to the “marvelous” asteroid Dinkinesh and its newly discovered satellite than first meets the eye, as NASA’s Lucy mission revealed.
As NASA’s Lucy spacecraft continued to return data of its first asteroid encounter on Nov. 1, 2023, the team was surprised to discover that Dinkinesh’s unanticipated satellite is, itself, a contact binary – that is, it is made of two smaller objects touching each other.
This image shows the asteroid Dinkinesh and its satellite as seen by the Lucy Long-Range Reconnaissance Imager (L’LORRI) as NASA’s Lucy Spacecraft departed the system. This image was taken at 1 p.m. EDT (1700 UTC) Nov. 1, 2023, about 6 minutes after closest approach, from a range of approximately 1,010 miles (1,630 km). From this perspective, the satellite is revealed to be a contact binary, the first time a contact binary has been seen orbiting another asteroid. Image credit: NASA/Goddard/SwRI/Johns Hopkins APL
In the first downlinked images of Dinkinesh and its satellite, which were taken at the closest approach, the two lobes of the contact binary happened to lie one behind the other from Lucy’s point of view. Only when the team downlinked additional images, captured in the minutes around the encounter, was this object’s true nature revealed.
“Contact binaries seem to be fairly common in the solar system,” said John Spencer, Lucy deputy project scientist, of the Boulder, Colorado, branch of the San-Antonio-based Southwest Research Institute.
“We haven’t seen many up-close, and we’ve never seen one orbiting another asteroid. We’d been puzzling over odd variations in Dinkinesh’s brightness that we saw on approach, which hinted that Dinkinesh might have a moon of some sort, but we never suspected anything so bizarre!”
A diagram showing the trajectory of the NASA Lucy spacecraft (red) during its flyby of the asteroid Dinkinesh and its satellite (gray). “A” marks the location of the spacecraft at 12:55 p.m. EDT (1655 UTC) Nov. 1, 2023, and an inset shows the L’LORRI image captured at that time. “B” marks the spacecraft’s position a few minutes later at 1 p.m. EDT (1700 UTC), and the inset shows the corresponding L’LORRI view at that time.
Image credit: Overall graphic, NASA/Goddard/SwRI; Inset “A,” NASA/Goddard/SwRI/Johns Hopkins APL/NOIRLab; Inset “B,” NASA/Goddard/SwRI/Johns Hopkins APL
Lucy’s primary goal is to survey the never-before-visited Jupiter Trojan asteroids. This first encounter with a small, main belt asteroid was only added to the mission in January 2023, primarily to serve as an in-flight test of the system that allows the spacecraft to continually track and image its asteroid targets as it flies past at high speed.
The system’s excellent performance at Dinkinesh allowed the team to capture multiple perspectives on the system, enabling the team to understand the asteroids’ shapes better and make this unexpected discovery.
“It is puzzling, to say the least,” said Hal Levison, principal investigator for Lucy, also from Southwest Research Institute. “I would have never expected a system that looks like this. In particular, I don’t understand why the two components of the satellite have similar sizes. This will be fun for the scientific community to figure out.”
This second image was taken about 6 minutes after closest approach from approximately 1,010 miles (1,630 km). The spacecraft traveled around 960 miles (1,500 km) between the two released images.
“It’s truly marvelous when nature surprises us with a new puzzle,” said Tom Statler, Lucy program scientist from NASA Headquarters in Washington. “Great science pushes us to ask questions we never knew we needed to ask.”
The team continues to downlink and process the remainder of the encounter data from the spacecraft. Dinkinesh and its satellite are the first two of 11 asteroids that Lucy plans to explore over its 12-year journey.
After skimming the main asteroid belt’s inner edge, Lucy is heading back toward Earth for a gravity assist in December 2024. That close flyby will propel the spacecraft back through the main asteroid belt, where it will observe asteroid Donaldjohanson in 2025, and then on to the Trojan asteroids in 2027.
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