How Will Water Flow on the Moon? New Research Brings Us Closer to Lunar Agriculture
If humanity is ever to establish a long-term, sustainable presence on the Moon, astronauts cannot subsist indefinitely on freeze-dried rations and pre-packaged meals launched from Earth. The logistical and economic costs of resupply missions alone make self-sufficiency not merely desirable, but absolutely essential. Growing fresh food on the lunar surface has therefore become one of the most pressing — and scientifically intricate — challenges of modern space exploration. Since raising livestock on the Moon presents near-insurmountable biological and ethical complexities, mission planners have largely converged on a plant-based agricultural solution. Yet before lunar greenhouses can become reality, scientists must grapple with a deceptively fundamental question: how does water actually behave under lunar gravity?
A team of researchers led by Karl Hasenstein of the University of Louisiana at Lafayette, and including John Kiss of the Florida Institute of Technology and Christopher McKay of NASA's Ames Research Center, recently published a landmark paper in Microgravity Science and Technology that systematically examines the physics of fluid behavior under lunar gravitational conditions. Their findings represent a critical step toward understanding how water — the single most vital ingredient for plant life — moves, clings, and pools in an environment that is profoundly alien to everything our agricultural science has ever known.
Why Lunar Agriculture Is So Complicated
Growing plants in space is not a new concept. NASA's Veggie facility and the Advanced Plant Habitat (APH) aboard the International Space Station (ISS) have been cultivating crops — from leafy greens to radishes — for years, providing not only nutritional supplementation but also invaluable psychological benefits for crews in long-duration spaceflight. In a remarkable demonstration of lunar agriculture's potential, researchers even managed to germinate Arabidopsis thaliana (thale cress) seeds in actual lunar regolith returned by the Apollo missions, proving that plant life can take root — however stubbornly — in Moon soil.
But there is a crucial distinction between growing plants in the microgravity environment of low-Earth orbit and growing them on the lunar surface, where gravity is approximately 1.62 m/s², or roughly one-sixth of Earth's gravitational pull. This so-called partial gravity regime sits in a scientifically murky zone between the familiar terrestrial gravity that shapes all of our agricultural intuition and the microgravity of the ISS, where entirely different physical forces dominate. Understanding this distinction is not merely academic — it has direct implications for how water infiltrates soil, how plant roots access moisture, and how oxygen reaches the root zone.
"The Moon's gravitational environment creates a fluid dynamics regime that is neither Earth-like nor truly microgravity — it is its own unique challenge, and one we have barely begun to characterize." — Research context from Microgravity Science and Technology
On Earth, fluid dynamics is overwhelmingly governed by gravity. Water infiltrates soil predictably, pulled downward in a well-understood manner that millennia of farming have taught us to harness. In microgravity, however, capillary forces take over entirely — surface tension and the adhesive properties of liquids become the dominant drivers of fluid movement. This makes it extraordinarily difficult to deliver water consistently to plant roots or to ensure adequate aeration of the root zone, since liquids tend to form floating globules rather than flowing predictably through a substrate.
Lunar gravity creates a third regime, one in which both gravitational and capillary forces play significant, competing roles. Predicting how water moves in this hybrid environment requires careful experimental measurement — and therein lies the problem. Until very recently, there was almost no reliable experimental data on fluid behavior at precisely lunar gravity levels.
The Challenge of Simulating Lunar Gravity
Replicating lunar gravitational conditions on Earth is notoriously difficult. Traditional techniques include drop towers, which provide only a few seconds of near-weightlessness, and parabolic arc flights — the so-called "vomit comets" — which can sustain reduced gravity for at most 20 to 30 seconds per parabola. While these tools have been invaluable for early microgravity research, they are wholly inadequate for studying the slower, more subtle dynamics of fluid behavior in lunar gravity. Many of the relevant processes — capillary rise, meniscus formation, surface wetting — simply take longer to manifest and stabilize than these brief windows allow.
Underwater neutral buoyancy tanks can approximate weightlessness for astronaut training, but they introduce water as the surrounding medium, which fundamentally alters the fluid physics being studied. Inclined planes and rotating systems can partially mimic reduced gravity for some mechanical purposes, but none of these approaches cleanly replicate the precise gravitational vector of the lunar surface for fluid dynamics experiments.
This is why the Hasenstein team's approach was so innovative — they leveraged an opportunity that most researchers would not have access to: a brief but scientifically invaluable window aboard a commercial suborbital spacecraft.
The New Shepard Experiment: Simulating the Moon on a Rocket
The researchers took advantage of a unique capability during the New Shepard 29 (NS-29) mission in February 2025. After booster separation, Blue Origin's uncrewed capsule activated its reaction control thrusters and began spinning at approximately 11 revolutions per minute (RPM). This rotation generated a centrifugal acceleration of approximately 1.76 m/s² — remarkably close to the Moon's actual surface gravity of 1.62 m/s². This centrifugally generated artificial lunar gravity was sustained for approximately two full minutes.
Two minutes may seem like a brief window, but it represents an improvement of orders of magnitude over parabolic arc flights. For fluid dynamics at lunar gravity, two minutes is sufficient to observe meniscus formation, capillary rise, and wall-wetting behavior — the precise phenomena the researchers needed to measure.
The experiment payload itself was an elegantly engineered autonomous device: a 3D-printed housing containing 18 individual fluid-filled test cavities, illuminated by LED backlighting and imaged by an Arducam camera system. The cavities were filled with three carefully chosen test liquids:
- Deionized water (dyed yellow) — the baseline reference fluid and the most agriculturally relevant
- A 30% glycerol solution (dyed blue) — a viscous fluid with known biological safety and osmotic regulation properties
- A 0.8% saline solution (dyed red) — approximating the ionic composition of plant-accessible soil water
The cavities themselves featured different internal wall geometries — vertical, angled at 15 degrees, and angled at 20 degrees — allowing the researchers to study how fluid behavior varied with surface orientation. By carefully tracking the shape of each liquid's meniscus (the curved surface formed where a liquid meets a solid boundary) across these different geometries, the team could apply a suite of hydrodynamic equations to extract fundamental physical parameters: surface tension, capillary length, and contact angle — all as functions of lunar-equivalent gravity.
Key Findings: What Happens to Water at One-Sixth Gravity
The experiment yielded several significant and scientifically illuminating findings that will directly inform the design of future lunar agricultural systems.
More Rounded Meniscus Profiles
The most visually striking result was that the curvature of the meniscus changed substantially under reduced gravitational acceleration. Compared to the relatively flat liquid surfaces seen at standard Earth gravity, menisci in simulated lunar gravity were noticeably more rounded and pronounced. This reflects the shifting balance between gravitational flattening forces and surface tension's tendency to minimize surface area — with less gravity pulling the liquid flat, surface tension's curvature effects become more dominant.
Thicker Wall-Clinging Films
In another significant finding, the reduced gravity environment allowed thicker liquid films to adhere to the cavity walls more effectively than in Earth gravity, producing liquid columns of greater height than standard Earth-gravity predictions would suggest. This enhanced wetting behavior has direct implications for how water might move through the microscale pore networks of lunar regolith, potentially allowing more effective capillary transport under the right conditions.
Discrepancies with Theoretical Predictions
Interestingly, the team also noted that both the measured surface tension and capillary length values were somewhat smaller than the theoretical textbook values for these fluids. The researchers attributed this discrepancy primarily to the microscopic surface texture of the 3D-printed chamber walls, which effectively function as a network of tiny conduits, artificially enhancing the wettability of the material beyond what smooth, idealized surfaces would exhibit. Secondary factors may have included the physical stresses of spaceflight itself — minor seal deformations, vibrations, or subtle wall interactions that are difficult to fully control in a flight environment.
This finding is itself scientifically valuable: it highlights that surface microstructure matters enormously in partial gravity fluid dynamics, a consideration that will be critical when designing containers, pipes, and soil beds for lunar agricultural systems.
Implications for Growing Food in Lunar Soil
While the experiment was focused on controlled laboratory fluids in engineered cavities, the researchers extended their analysis to the real-world challenge of working with actual lunar regolith — and the picture that emerges is formidably complex.
Raw lunar regolith is one of the most hydraulically hostile substrates imaginable. The topmost layer is composed of extremely fine, electrostatically charged dust particles that are intensely hydrophobic — they actively repel water rather than absorbing it. Trying to irrigate through this layer is like trying to water soil covered in a thin film of wax. Beneath this, the grain size of lunar soil increases with depth, creating larger pore spaces that cause water to drain rapidly downward rather than being retained near the surface where roots could access it. Eventually, this percolating water must accumulate somewhere, potentially forming stagnant, oxygen-depleted reservoirs that could suffocate plant roots through anoxia.
Glycerol as a Potential Agricultural Regulator
One of the most promising practical outcomes of the experiment was the performance of the glycerol solution. In the test cavities, glycerol demonstrated markedly superior wetting characteristics compared to both water and saline — it spread more effectively across surfaces and formed more stable films. Crucially, glycerol is already well-established in plant biology as a safe and effective osmotic regulator, and it is a naturally occurring metabolic compound in many organisms. This raises the intriguing possibility that future lunar plant beds could be supplemented with glycerol alongside water, potentially improving soil wettability, moderating water availability to roots, and reducing the hydraulic hostility of raw regolith.
A glycerol-augmented irrigation strategy could serve a dual purpose on the Moon: improving water distribution through hostile regolith while simultaneously providing plants with a biologically compatible osmotic buffer against the stresses of the lunar environment.
Alternative Approaches: Hydroponics and Soil Engineering
Of course, working directly with raw lunar soil is only one potential path forward. Hydroponics — growing plants in nutrient-enriched water solutions without soil — sidesteps many of the regolith's hydraulic challenges entirely. Hydroponic systems have already demonstrated considerable success aboard the ISS, and they could, in principle, be established on the lunar surface in pressurized habitats. However, they come with their own significant challenge: all the equipment, growing medium, and nutrient solutions would initially need to be transported from Earth, at extraordinary cost.
Researchers have also explored the use of soil bacteria to chemically alter lunar regolith, improving its water retention and biological compatibility. Studies have shown that certain microbial communities can break down regolith minerals, releasing nutrients and modifying surface chemistry in ways that make the soil more hospitable to plant roots. Combining microbial soil treatment with glycerol supplementation and an understanding of partial-gravity fluid dynamics could eventually yield a viable in-situ agricultural system.
The Scale of the Challenge
To appreciate the magnitude of what lunar agriculture must ultimately achieve, consider this sobering estimate from mission planners: a crew of just six astronauts would require approximately 650 square meters of functional crop-growing area to achieve meaningful food self-sufficiency. That is roughly the footprint of a large house — and it must be maintained, irrigated, harvested, and replanted continuously, in a radiation-intensive, vacuum-adjacent environment where every kilogram of equipment, every liter of water, and every gram of soil amendment represents a massive logistical investment.
This scale makes it abundantly clear why understanding the fundamental physics of water in lunar gravity is not a peripheral scientific curiosity — it is a foundational prerequisite. Every design decision in a lunar agricultural system, from the geometry of irrigation channels to the composition of growth media, will be shaped by how water actually moves, wets, and drains in one-sixth gravity.
For further reading on the state of lunar exploration and the infrastructure challenges it poses, the European Space Agency's Moon Village concept provides valuable context, as does NASA's Artemis program, which aims to return humans to the lunar surface and establish a sustained presence there in the coming decade.
Looking Ahead
The NS-29 experiment represents exactly the kind of foundational, unglamorous science that makes bold human achievements possible. By carefully measuring meniscus curvature and capillary lengths in a spinning rocket capsule 100 kilometers above Earth, Hasenstein, Kiss, McKay, and their colleagues have added a crucial data point to our understanding of a physical regime that no textbook has fully characterized — because, until very recently, we had almost no way to measure it.
Future experiments will need to test a wider range of fluids, surface materials, and gravity levels. Ideally, experiments conducted on the lunar surface itself — perhaps as part of Artemis-era science payloads — will eventually provide ground truth data to validate and refine the models being developed now. Research into NASA's plant biology programs continues to push the boundaries of what is possible in space agriculture.
But for now, each incremental step — each carefully analyzed meniscus, each measured capillary length — brings us meaningfully closer to the day when a lunar farmer might look out across rows of growing crops, nourished by water flowing in ways that Earth-bound intuition could never fully predict, and know that humanity has truly learned to live among the stars.
- Gravity on the Moon: ~1.62
