Exciting new details are emerging about an asteroid flown by NASA’s Lucy spacecraft last year
Last year, NASA’s Lucy spacecraft encountered a bilobed asteroid, a piece of a larger, rocky body that was shattered in a great collision 155 million years ago. This little stop happened on Lucy’s way to an encounter with the Trojan asteroids shadowing Jupiter around the Sun.
the asteroid 52246 Donald Johansson, known as “DJ” L LucyMission Scientists The mission, named after the paleontologist who discovered the hominin fossil Lucy in Ethiopia in 1974, orbits the planet. sun In the inner part of the main Asteroid belt between Mars and Jupiter.
The real Lucy fossil dates back to 3.2 million years ago, and is an important link in the evolutionary chain that led to Homo sapiens. Likewise, primitive asteroid bodies are somewhat similar to the fossilized remains of the asteroid’s basic units Solar systemPlanets, incl land. Understanding the composition of these asteroids and where they formed versus where they are today can provide important insights into how Earth was assembled and where its organic materials and water came from.
Lucy flew by DJ in April of 2025. It’s a very primitive asteroid, which means it has, or once had, certain volatiles like water ice, as well as a lot of carbon, all things that can be removed thermally over time. Most objects containing volatile materials originate in the outer solar system, where it is cold enough that the volatiles do not fly away.
Within DJ’s composition, Lucy discovered iron-bearing foliar silicates, a mineral that forms in the presence of liquid water.
“Phyllosilicates are an indicator that water is present, and that there is some degree of hydrological alteration,” Simone Marchi, a planetary scientist from the Southwest Research Institute and study leader at DJ, told Space.com.
However, for DJ to have water, it must have formed far from the Sun, perhaps in the outer asteroid belt.
“But DJ belongs to the inner asteroid belt, so that’s really interesting,” Marchi said.
Spectroscopic evidence also suggests that DJ was only partially altered by water, which Marchi says tells us something about its history.
“The water change ended early, and although we don’t know why, we can speculate. In order to get the water change there must be some internal heating.” [usually via radioactive elements] If something formed later than something else, there would be less heat [since many of the radioactive elements will have already decayed]. “Or perhaps there was less water initially where it formed.”
What we do know is that DJ was once part of a much larger asteroid that underwent a massive impact 155 million years ago, causing the original body to break up into a number of pieces, the largest of which is the 45-mile (73-kilometer)-wide asteroid 163 Erigone. Thus, the remains of this parent asteroid, including DJ, are collectively referred to as the Erigone family.
The DJ’s violent origin may also explain its shape, which features two lobes joined together by a narrower, relatively smooth neck.
“We have now seen many small objects in the solar system that appear to have this bilobed shape, across a wide range of sizes,” Marchi said.
For example, the near-Earth asteroid 25142 Itokawa, which was visited by the first Japanese Hayabusa mission in 2005, and 4149 Toutatis encountered by China’s Chang’e 2 spacecraft in 2012, both are bilobites. As well as the small asteroid Salam, which is a satellite of the asteroid 152830 Dinkenish Lucy visited her In 2023. Then there are the comets including 67P Churyumov-Gerasimenko, which has been visited by Rashid The mission and comet 19P/Borrelly, imaged by NASA’s Deep Space 1 spacecraft in 1999.
These objects are all different sizes, different types, and in different locations, but they all share the same structure. However, Marchi warns that they may not all be shaped the same way. For example, the neck is between the lobes Comets Such as 67P it may form through erosion by sublimation and outgassing as the comet approaches the Sun, while for asteroids it may indicate a history of involvement in a giant impact, with the resulting fragments coming together to bind gravitationally – a so-called binary contact.
Lucy now continues to move forward, and is scheduled to encounter its first Trojan asteroid, known as 3548 Eurybates, in August 2027. Trojans are asteroids captured by Jupiter’s gravity at L3 and L4. Lagrange points60 degrees in front of Jupiter and 60 degrees behind Jupiter itself.
“We think that the Trojans, based on our understanding of the solar system, formed farther away and then were captured where they are today after the early mixing of the planets,” Marchi said. “It is also possible that this mix-up is the origin of DJ, so there may be a connection between DJ and the Trojans.”
Compositionally, the majority of Trojans are expected to be more primitive than DJ, containing more carbon, water and other volatiles that would sublimate if they got too close to the Sun.
That’s all except one: Eurybates.
“It’s the only one of our targets that from spectroscopic analysis looks relatively similar to DJ,” Marchi said. “It’s not identical, but it’s closer in composition to DJ than other Trojans, so it would be interesting to compare them.”
In fact, any similarities will help tell us how asteroids were clumping together during the first hundreds of millions of years of the solar system’s history after the planets formed. Jupiter and SaturnIn particular, migration began inward and then outward again. In doing so, their gravity pushed and pulled the small objects everywhere, just as gravity did Uranus Especially Neptune They also headed abroad. These migrations led to the formation of the asteroid belt and the planet Earth Kuiper beltAnd trillions of objects were thrown into the vast orbits of the planet Oort cloud.
“The main question is, if DJ was transported into the inner asteroid belt, how many other asteroids came with it and ended up being closer to Earth, where they could have delivered some water and some organics and other things to our planet?” Marchi asked.
Lucy will visit six of Jupiter’s Trojans, totaling more than 15,300 discovered so far. Beyond the masses of rock, the Trojans, along with DJ and Dinkenesh (the Ethiopian name for Lucy’s fossil), are windows into the past, storytellers of Earth’s oldest history.
Lucy’s findings from Donald Johansson were published on Thursday (June 18) in the journal sciences.
