Roid Rage Boulders All the Way Down
Mar 19, 2026
Andy Ryan, senior payload scientist at AstroForge and former lead on OSIRIS‑REx thermal analysis, explains how Bennu turned out to be a boulder-strewn surprise. Short chats cover why missions expected sand, the TAG sampling drama, thermal tools like lock-in thermography and CT scans, and what porous, cracked rocks mean for mining, planetary defense, and future low-cost asteroid visits.
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Thermal Inertia Reveals Surface Texture
- Thermal inertia measures how quickly a surface heats and cools, revealing particle size or rock solidity without visiting the surface.
- Andy Ryan used lab experiments and models to predict particle sizes from thermal swings, guiding OSIRIS-REx sampling site selection.
Apparent Smooth Patches Were Bouldery
- High-resolution imagery showed smooth-looking patches were actually covered in meter-scale boulders, not fine regolith.
- Initial telescopic and radar data misled teams because resolution improvement revealed pervasive boulders.
Boulders Appeared Highly Porous From Remote Data
- Surface boulders exhibited unexpectedly high porosity estimates from remote data, suggesting void fractions far above meteorite analogs.
- Simple models implied ~50% void space, much higher than ~20–30% seen in known meteorites.