Cosmic radiation destroys organic molecules. On Mars, where there is no protective magnetosphere and only a thin atmosphere, the surface is sterilized. Any amino acids — the building blocks of proteins and the most durable biosignatures — would be broken apart within a few hundred million years even meters underground. The search for evidence of past life on Mars has therefore focused on rocks and clays, where mineral matrices might shield organics from radiation.
Pavlov and colleagues (NASA Goddard and Penn State, Astrobiology 2026) tested a different substrate: ice. They froze E. coli amino acids in pure water ice and in Mars-like sediment, then irradiated both at minus 60 degrees Fahrenheit — matching conditions in Martian icy regions — with gamma radiation equivalent to 20 million years of cosmic ray exposure on the Martian surface.
In sediment, amino acids degraded ten times faster and did not survive. In pure water ice, more than ten percent survived the full exposure — extrapolating to over 50 million years of preservation.
The mechanism: radiolysis products — the reactive fragments created when radiation hits water — get frozen in place. In liquid water or porous sediment, these fragments diffuse and react with whatever organic molecules they encounter. In solid ice, they cannot move. The damage is created but cannot reach its target. The shield is not absorption or deflection but immobilization. The ice does not block the radiation. It freezes the consequences.
The general principle: protection does not require blocking the threat. It can be achieved by preventing the secondary effects from reaching the vulnerable target. The distinction between blocking and immobilizing is invisible until you test the right substrate. Rock-based preservation blocks radiation through mass. Ice-based preservation immobilizes radiolysis products through phase. The radiation gets through in both cases. What changes is whether its products can move.