Will humankind colonize other star systems, spreading life to distant worlds? Or more locally, and realistically: will we ever establish settlements on Mars or the Moon? Before we even consider stuff like huge generation ships, we have to look at our biology. Can our fragile forms reproduce in space, allowing our off-world outposts to sustain themselves?

That’s what Chinese scientists hope to find out. This month, China sent a batch of synthetic human embryos to its Tiangong space station, in a first-of-its-kind experiment to explore how a critical early stage of human development is affected by a microgravity environment.

The samples are made of human stem cells and closely resemble real embryos, but aren’t capable of developing into an actual fetus.

“This is not a real human embryo and does not have the ability to develop into an individual. However, it can serve as a model for studying early human development,” project leader Yu Leqian, a researcher at the Chinese Academy of Sciences’ Institute of Zoology, said in a statement.