Next, the experts converted those values into a“ relative optical density” scale from zero to one. Ground controls on Earth matched the same temperature changes over time and used the same photo method.
They lacked the space environment, which let the team ask,“ Did the fungus grow differently up there than it did down here?”
What the growth data suggested
Inside the hardware on the ISS, the temperature rose quickly and then settled at an average of about 89 ° F( 31.5 ° C). Under those conditions, the fungus reached full coverage of the agar.
When the authors modeled the growth curve, they estimated the on‐orbit growth rate was about 1.21 times the ground control rate( about 21 % higher).
The researchers described this pattern as consistent with a possible“ radioadaptive” response. Radiation could play a role, but microgravity also changes how fluids move and how cells interact, which can affect growth.
ISS radiation sensors
The radiation sensors did not function as the dose badges you may have heard about in medical imaging.
The sensors counted ionizing events, but they did not directly report a clean“ dose” value in millisieverts for the experiment.
Because both sensors ran under the same dish at the same time, the design allowed a direct comparison.
Over the full runtime, the sensor under the fungal side recorded slightly fewer counts per minute than the sensor under the control side, about 147 versus 151 counts per minute.
The difference also changed with time. Early in the run, the sensors tracked closer together because the fungal layer still looked thin.
Later, after the fungus built up a stable layer, the separation grew. That timing made it less likely that one sensor was simply reading low from the start.
Why melanin and water matter
Melanin is central to the hypothesis. Radiation can create reactive molecules, and melanin can absorb energy and help neutralize some of the chemical damage those molecules cause.
The study also points to a simpler materials lesson: hydrogen‐rich materials often help slow certain kinds of space radiation, especially energetic protons and neutrons.