Growing Plants in Space: Manipulating Medium Wettability to Create Different Saturation Conditions

Growing plants under microgravity conditions in a space ship is essential for future long-term missions to supply needs for food and oxygen. Although plant growth modules for microgravity have been developed and tested for more than 40 years, creating optimal saturation conditions for plant growth in the absence of gravity still remains a challenge. In this study, we present results from a series of spontaneous imbibition experiments designed to approximate microgravity conditions by using density-matched fluid pairs. Porous media with patterned wettability characteristics are used to manipulate macroscopic fluid saturation and microscopic fluid interfacial configurations. These are compared to an additional experiment under Earth gravity, wherein we observe spontaneous imbibition of water into common potting soil. Patterning grains of different wettabilities under microgravity conditions proves to be an effective method to manipulate spatial distributions and saturations of fluids. These wettability patterns can be optimised to fine-tune residual fluid characteristics, e.g. non-wetting phase saturation, connectivity and interfacial area. Furthermore, we present tomographic evidence supporting previous work which was suggesting enhanced snap-off and disconnection of the gas phase in porous media under microgravity.