The moon that was discovered last week around asteroid Dinkinesh surprisingly turns out to consist of not one but two parts.
A few days ago, space probe Lucy flew past asteroid 152830 Dinkinesh. The flyby confirmed what astronomers had suspected for some time, that the space rock is accompanied by a very small moon. But not just any moon, as new images show. Dinkinesh’s natural satellite appears to consist of two parts.
Lucy’s mission
Space probe Lucy was launched more than two years ago. The intention is for the probe to visit various asteroids and so-called Trojans over the next ten years. These Trojans are remnants of the material from which the outer planets of our solar system formed. In this way, researchers hope to gain more insight into the conditions that contributed to the formation of our solar system more than four billion years ago.
More about the mission
As Jupiter follows its orbit around the sun, it is accompanied by a large group of asteroids, known as Trojans, that travel in front of and behind the planet. We have actually never looked at these Trojans up close. But that is now changing thanks to the mission of the American space probe Lucy, which was launched in October 2021. A mission that has, by the way, been considerably improved over time. Initially, Lucy was supposed to reveal the secrets of six Trojans – Eurybates, Polymele, Leucus, Orus, Patroclus and Menoetius – and an asteroid from the asteroid belt named Donaldjohanson. But later it was discovered that both Eurybates and Polymele have a small moon. This led to the decision to also thoroughly investigate these moons. Moreover, last January it was decided that Lucy would also treat 152830 Dinkinesh to a visit. As a result, the list of space rocks to investigate has become longer and longer.
Last week Lucy flew past her first target: 152830 Dinkinesh. This is an asteroid with a diameter of 790 meters that was only discovered in 1999 due to its modest size. This small space rock follows an elliptical orbit, meaning its distance from the sun ranges from 180 million to 225 million miles. Dinkinesh is the smallest asteroid in the asteroid belt between Mars and Jupiter ever visited by a spacecraft.
Moony
The first images returned from Lucy clearly showed Dinkinesh being accompanied by a small companion. But it now appears that there is more to this asteroid and its newly discovered satellite than meets the eye. New images keep trickling in all the time. And these images now clearly show that the moon is a so-called ‘contact binary object’. This means that it consists of two smaller objects that make physical contact with each other.
In a row
In short, Dinkinesh’s moon consists not of one, but of two parts. It is easy to explain why astronomers are only now discovering this. In the first photos, taken at closest approach, the two parts of the moon happened to be right behind each other from Lucy’s point of view. However, the probe took many more photos in the minutes that followed. And only then did the true nature of the moon come to light.
Contact binary objects
The discovery that Dinkinesh’s moon consists of two parts is remarkable but not particularly unusual. “Contact binary objects are quite common in our solar system,” notes researcher John Spencer. “However, we have not often had the opportunity to study these objects up close, and in fact we have never seen one orbiting another asteroid. However, during the flyby of Dinkinesh we saw unusual brightness variations, which led us to suspect that the asteroid had a moon. But we never expected something so amazing!”
Puzzling
It means that Dinkinesh consists of not one or two, but no fewer than three components. “This is puzzling to say the least,” said lead researcher Hal Levison. “I never thought a system could look like this. What I don’t understand in particular is why the two parts of the moon are similar in size. This promises to be an exciting challenge for the scientific community to unravel.”
Reis
Meanwhile, Lucy continues her journey. Dinkinesh and her natural satellite are the starting point of Lucy’s mission to explore various interesting space rocks over a 12-year period. The probe will now first set course for Earth again, and then use a gravity pendulum to head towards asteroid 52246 Donaldjohanson. From there, Lucy heads on to her main targets: the Trojans. If all goes according to plan, Lucy will become the first spacecraft to visit these ancient remnants of our solar system. The intention is that several Trojans will be explored between 2027 and 2033.
As Lucy heads towards her next destination, the team will continue to analyze the remaining data from the brief encounter with Dinkinesh. Because there is still plenty to unravel about this mysterious object. “It’s truly amazing when nature surprises us with a new mystery,” says team member Tom Statler. “Good science encourages us to ask questions we didn’t even know we had to ask.”