NASA's Lucy spacecraft has revealed fascinating insights into the asteroid 52246 Donaldjohanson, or DJ, a bi-lobed asteroid that is a fragment of a larger rocky body shattered in a colossal collision 155 million years ago. This discovery, detailed in a recent study, sheds light on the solar system's evolution and the origins of Earth's organic materials and water.
The asteroid, named after the paleoanthropologist who discovered the Lucy hominin fossil, orbits the sun in the inner part of the main asteroid belt between Mars and Jupiter. Its primitive nature suggests it once contained volatile materials like water-ice and carbon, which can be thermally removed over time. Interestingly, Lucy detected iron-bearing phyllosilicates within DJ, indicating the presence of liquid water in its past.
What's intriguing is that DJ's composition suggests it formed further out from the sun, possibly in the outer asteroid belt, and then migrated to its current location. This migration is supported by the spectral evidence, which indicates that DJ was only partially altered by water, implying an early termination of aqueous alteration. The study's lead, Simone Marchi, speculates that internal heating, possibly from radioactive elements, played a role in this process.
The bi-lobed shape of DJ is also noteworthy, resembling other small bodies in the solar system, such as near-Earth asteroids Itokawa and Toutatis, as well as cometary bodies like 67P Churyumov–Gerasimenko. Marchi suggests that these shapes might result from different processes, such as erosion or giant impacts, highlighting the complexity of asteroid formation.
Looking ahead, Lucy will encounter its first trojan asteroid, 3548 Eurybates, in 2027. Trojans are asteroids captured by Jupiter's gravity at Lagrange points, and they are expected to be even more primitive than DJ. The comparison between DJ and Eurybates will provide valuable insights into the solar system's early history and the migrations of Jupiter, Saturn, Uranus, and Neptune.
The study raises an important question: if DJ has been relocated to the inner asteroid belt, how many other asteroids accompanied it and ended up closer to Earth, potentially delivering water and organics to our planet? This discovery underscores the significance of Lucy's mission in unraveling the mysteries of our solar system's formation and evolution.
