Dinkinesh has a moon! But that's not all... Lucy Mission Update
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| Dinkinesh with its moon in the background as seen by the Lucy spacecraft at closest approach. Credit: NASA/Goddard/SwRI/Johns Hopkins APL/NOIRLab |
On November 1, 2023, NASA's Lucy spacecraft approached within 425 Kilometres of Dinkinish, the smallest main belt asteroid yet explored, with a relative velocity of 4.5 kilometres per second. This was Lucy's first target after launch.
Launched on October 16, 2023, Lucy's original mission was to fly by one main belt asteroid and six Trojan asteroids. Trojans are asteroids that are trapped in gravitationaly stable regions in front of, and behind, planets. Every planet has Trojan asteroids except Mercury and Venus, due to their proximity to the Sun, which makes orbits more unstable and chaotic for small bodies.
The main goal of the Lucy mission is to investigate the unexplored Jupiter Trojans, (though the Trojans of other planets are also unexplored). Some of these Trojans may hold clues to the evolution of our solar system.
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| Lucy's original 7 Targets. Credit: NASA/Goddard Space Flight Center Conceptual Image Lab |
The original plan when the mission was being developed was to visit 1 or 2 Trojans, but after tweaking the trajectory, the mission team was able to work out flybys of 6 Trojans, and 1 main belt asteroid. (The main belt asteroid was named Donaldjohanson, after the discover of the Lucy fossil, the mission's namesake).
Before launch, a moon was discovered around Lucy's first Trojan target: Eurybates, which was named Queta ("Ket-ah"). After launch, a satellite was discovered around Lucy's second target: Polymele. While this satellite is yet to be officially named, members of the Lucy team have nicknamed it "Shaun."
In early 2023, asteroid 1999 VD57 was selected as an additional target for a flyby in November. Because of its small size, the asteroid was overlooked at first. Shortly after the announcement, the asteroid was named Dinkinesh (ድንቅነሽ in Amharic, the language of Ethiopia). Dinkinesh means "you are marvelous," and is the Ethiopian name for the mission's namesake fossil.
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| Dinkinesh moving againsted the background stars. Credit: NASA/Goddard/SwRI/Johns Hokins APL |
Ahead of the flyby, scientists used old WISE (later renamed NEOWISE) data from 2010 to revise estimates of the asteroid's diameter, which was predicted to be around 760 meters. Scientist's also noticed brightness variations that indicated that Dinkinesh might possess a satellite. And boy does it!
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| Trajectory and orientation of the Lucy spacecraft during the Dinkinesh encounter. Credit: NASA/Goddard/SwRI/Johns Hopkins APL/NOIRLab |
The images released so far show that Dinkinesh possesses a moon with a diameter of around 220 meters. While this in itself was interesting, the moon turned out to be weirder than anyone thought. On November 7, NASA announced that the moon consisted of two objects, making it a contact binary. While contact binaries have been seen, and even studied up close by spacecraft before, this was the first time a contact binary moon has been confirmed (several moons of Neptune are believed to be possible contact binaries, but images are too low resolution to confirm if they actually are).
Over the next few weeks, months, and years, scientists will piece together the origin of Dinkinesh and it's unusual satellite. Lucy is on its way back to Earth for a gravity assist in 2024, with a flyby of Donaldjohanson in 2025.
Lucy will fly be Jupiter's L4 trojans in 2027 and 2028, and a binary Trojan system in the L5 group in 2033. While Lucy's number of targets is now at 11, it's quite possible that every target the spacecraft will visit has a moon or two.
The Targets
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| Dinkinesh with background moon removed. Credit: NASA/Goddard/SwRI/Johns Hopkins APL/NOIRLab/Orchard |
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| Dinkinesh's unnamed moon. Credit: NASA/Goddard/SwRI/Johns Hopkins APL |
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