The successful launch of the Tianzhou 10 cargo spacecraft on May 11 carried human embryo models into space. This marks the world's first in situ experiment to explore how microgravity and cosmic radiation affect early human development under space conditions — a crucial step toward understanding whether humans can one day live and reproduce in space.

The mission is expected to help scientists establish a technical framework for studying artificial embryo development beyond Earth.

Rather than being real human embryos, these are "embryo-like structures" created in a laboratory using stem cells. They closely mimic the structure of a natural early human embryo but carry fewer ethical restrictions, can be produced in large quantities, and offer highly reliable, repeatable results.

Crucially, these models possess the ability to mimic early cellular growth and follow the most critical stages of early human development. However, they are not real embryos and cannot develop into a human being.

Yu Leqian, a professor at the Chinese Academy of Sciences' Institute of Zoology and head of the project aboard Tianzhou 10, said these models cover the developmental stage from day 14 to 21 after fertilization.

"This stage is a critical window in early human development, during which the building blocks for future organs begin to form, and the entire body axis — which determines the head and the tail — is established," Yu said. He noted that any disturbance at this stage could have a profound impact on an adult individual.

"Therefore, these models were brought to space to explore whether life, which has evolved under gravity for hundreds of millions of years, is affected by its sudden absence," he added.

Ground-based simulations cannot fully replicate the unique environment of space.

The Tianzhou 10 launch provides a rare, true microgravity environment complete with actual space radiation. The embryo models are expected to grow naturally in orbit. A preprogrammed system will automatically replace the liquid culture nutrients every day, allowing the models to complete five days of development. Afterward, the samples will be frozen and stored, ready for analysis upon their return to Earth.

Two specific types of models have been sent to the Chinese space station, Tiangong, to study key milestones in early life. The first is a peri-implantation model, which mimics the critical phase where an embryo attaches itself to the uterine wall. The second is a peri-gastrulation model, which replicates gastrulation, a fundamental event in early development where a single layer of cells reorganizes into the distinct layers that will eventually form different tissues and organs.

"By comparing embryo development in space with that on the ground, we can investigate how the space environment impacts critical events in human development," Yu said. "We can also assess how accurately these models can substitute for natural embryos in space studies, thereby laying a technical foundation for future research."

Yu highlighted that the study will help reveal the risks and challenges humans might face during long-term space habitation, particularly regarding reproduction. Furthermore, by comparing space-grown models with those on Earth, the research could provide fresh insights into which human diseases are linked to abnormalities during the earliest stages of life.