Lost in Space: In Zero Gravity, Sperm Lose their Sense of Direction

Starting a family off-Earth might be more difficult than expected. New research from the University of Adelaide shows that sperm have trouble orienting themselves in zero gravity, suggesting that gravity plays a crucial role in helping them reach an egg.

Significant Decline in Sperm Count

Scientists from the Robinson Research Institute, the School of Biomedicine, and the Freemasons Centre for Male Health and Wellbeing investigated how space-like conditions affect sperm orientation, fertilization, and early embryonic development. To simulate microgravity, the researchers used a 3D clinostat device developed by Dr. Giles Kirby at Firefly Biotech. This device continuously rotates the cells to mimic the disorienting effects of weightlessness. Sperm from three different mammals, including humans, were tested by passing them through a maze modeled after the female reproductive tract. “This is the first time we have been able to demonstrate that gravity is a key factor in sperm’s ability to navigate a channel such as the reproductive tract,” said lead author Dr. Nicole McPherson of the Robinson Research Institute at the University of Adelaide.

Under microgravity conditions, the researchers observed a significant decrease in the number of sperm that were able to successfully navigate the chamber maze compared to normal gravity. This was observed in all models, even though the way the sperm physically moved had not changed. This suggests that their loss of orientation was not due to a change in motility, but to other factors.

Impairment of Fertilization and Embryonic Development

The researchers also found that the addition of the sex hormone progesterone improved the navigational ability of human sperm under simulated microgravity conditions.” “We believe this is because progesterone is also released from the egg cell and can help guide the sperm to the site of fertilization, but this needs to be investigated further as a potential solution,” said Dr. McPherson.

The team investigated how exposure to microgravity during fertilization affects early embryonic development in animal models. After four hours in simulated weightlessness, the number of successfully fertilized mouse eggs dropped by 30 percent compared to normal conditions on Earth. “We observed reduced fertilization rates during a four- to six-hour exposure to microgravity. Longer exposure appeared to be even more detrimental, leading to developmental delays and, in some cases, a reduction in the cells from which the fetus develops during the earliest stages of embryo formation,” said Dr. McPherson. These findings demonstrate how complex reproductive success is in space and how urgently further research is needed across all early stages of development.

Why Gravity Is Important for Reproduction

Previous research has examined how sperm move in space, but until now, no study had tested their ability to navigate through a reproductive tract under controlled conditions such as these. The results were published in Communications Biology. This study was conducted in collaboration with the University of Adelaide’s Andy Thomas Centre for Space Resources, which focuses on the challenges of long-term space exploration and life beyond Earth.

“As we move toward becoming a spacefaring or multiplanetary species, it is crucial to understand how microgravity affects the earliest stages of reproduction,” said Associate Professor John Culton, Director of the Andy Thomas Centre for Space Resources.

Future Research on Reproduction in Space

The next phase of research will examine how different gravity environments—including those on the Moon, Mars, and in artificial gravity systems—affect sperm navigation and early embryonic development. A key question is whether these effects change gradually as gravity decreases, or whether there is a threshold beyond which changes occur suddenly, triggering an “all-or-nothing” response.

Answering this question will be crucial for planning human reproduction in future lunar and Martian settlements, as well as for developing artificial gravity systems that support healthy development. “In our latest study, many healthy embryos were able to form even when fertilized under these conditions. This gives us hope that reproduction in space might one day be possible,” said Dr. McPherson.