Fine-regolith production on asteroids controlled by rock porosity

Area of Science:

• Planetary Science
• Asteroid Surface Processes
• Regolith Physics

Background:

• Spacecraft missions have observed unconsolidated regolith on stony asteroids.
• Telescopic data suggested regolith on carbonaceous asteroids (e.g., Bennu, Ryugu).
• Observed comminution processes contrast with the lack of extensive regolith on Bennu and Ryugu.

Purpose of the Study:

• To investigate the reasons for the apparent lack of extensive regolith on carbonaceous asteroids.
• To determine the relationship between rock porosity and subcentimetre particle abundance on asteroid Bennu.
• To infer the prevalence of regolith blankets on different asteroid types.

Main Methods:

• Analysis of spacecraft mission data from asteroid Bennu.
• Correlation analysis between local subcentimetre particle abundance and rock porosity.
• Comparison with laboratory experiments on rock fragmentation and thermal cracking.

Main Results:

• An inverse correlation was found between subcentimetre particle abundance and rock porosity on Bennu.
• Highly porous rocks on Bennu are compressed by impacts, not fragmented.
• Thermal cracking is slower in highly porous rocks compared to denser ones.

Conclusions:

• Accumulation of unconsolidated subcentimetre particles is hindered on highly porous asteroid surfaces.
• Regolith blankets are likely uncommon on carbonaceous asteroids due to their high rock porosity.
• Regolith terrains are predicted to be common on less porous stony asteroids.