Those weird "blueberries" all over Mars are all the exact same size because they literally can't grow any bigger than the dust in the air.
arXiv · March 13, 2026 · 2603.11143
Why it matters
For decades, the uniform size of these 1–6mm stones was a mystery, but new research shows that Martian dust acts as a physical bottleneck to their growth. The rocks stop growing exactly when they hit a specific size dictated by the microscopic gaps between dust grains in the Martian soil.
From the abstract
Diagenetic concretions have been identified at multiple widely separated sites on Mars, including Meridiani Planum (Opportunity), Gale crater (Curiosity), and Jezero crater (Perseverance). Solid concretions at all sites fall within the millimetre size range (typically 1-6 mm diameter), despite differing cement mineralogies. The one substantial outlier -- centimetre-to-decimetre-scale hollow concretions on Bradbury Rise -- formed in coarser basaltic sandstone via a distinct mechanism. I propose t