The dream of becoming a multi-planetary species is only a few generations away for some visionaries. A more concrete question, however, gets asked whenever a long mission is discussed: if you send a family to Mars, where will their children come from? No human has ever conceived in space, so the honest answer remains unknown.
To get the first real data, Chinese researchers sent a batch of "human artificial embryos" aboard the Tianzhou-10 cargo ship to the Tiangong space station. The samples are not embryos in the ordinary sense. They are clusters of living stem cells coaxed into a spherical shape that imitates the structure of a natural human embryo roughly a week after conception. Crucially, they cannot develop into a fetus — they are a model, designed to mimic development as closely as possible while staying within ethical limits.
Why bother with a model rather than real gametes? Because studying natural eggs and sperm would require far more delicate handling and much larger experiments. The artificial structures let scientists watch how dividing cells respond to weightlessness and cosmic radiation at a magnified pace, capturing the very first moments where a single fertilized egg would split and begin to form a body plan.
The context for the experiment is sobering. Separate work using rotating machines to mimic microgravity has already shown that human sperm struggle to navigate toward an egg in a weightless environment, with fertilisation success falling by around thirty per cent. A recent study on germ cells — the earliest cells that eventually become sperm or eggs — found that, in space conditions, these cells take roughly twice as long to produce their first daughters and grow noticeably slower overall.
Radiation adds a second layer of risk. Earth is protected by its magnetic field and atmosphere; in orbit, cells are hit constantly by high-energy particles that can damage DNA at the moment a new organism is being assembled. If the very first divisions of an embryo are disrupted, the consequences ripple through an entire life.
So what are researchers looking for in the payload? They want to know whether cells can still find each other, stick together, orient themselves, and begin to specialise the way they would in a womb on Earth. The answers will shape everything from the design of long-duration life support to the ethics of colonisation. If reproduction in space proves fundamentally impaired, the vision of children born on Mars may require very different technology — perhaps artificial gravity, radiation shielding, or even medical intervention before conception.