Boulders on asteroid Ryugu are surprisingly fluffy, Hayabusa2 finds
Boulders on asteroids can be three-quarters hollow or more, a discovery that could help yield insights on how Earth and other planets formed. The earliest stage of planetary formation started with building blocks known as planetesimals, chunks of rock ranging in size from asteroids to dwarf planets. Research suggested planetesimals began as very porous, fluffy clumps of dust that heat, gravity and impacts compacted over time.
Japan’s Hayabusa2 spacecraft found that Ryugu, a diamond-shaped near-Earth asteroid, is covered with rocks that are about 30 to 50 per cent porous. Now scientists have found that those boulders may be more than 70 per cent empty space, or about as porous as prior work suggested ancient planetesimals were, suggesting the rocks may contain remnants of the early Solar System.
The researchers noted that Ryugu’s hotspot boulders are about as porous as the bodies of comets. Prior work noted that comets are likely remnants of the original planetesimals, and now scientists are suggesting that Ryugu’s hotspot boulders may similarly be remnants of ancient planetesimals which cosmic impacts blasted out from under Ryugu’s surface.
Uncovering details about the original nature of planetesimals could shed light on how the planets formed after the Sun was born. For example, the scientists previously noted that if planetesimals are as fluffy as researchers increasingly suspect, then they might have crumbled more easily during impacts, making them less likely to eject fragments with great force to shatter other asteroids.