Back in the 1990s, when we had the space shuttles available for ferrying stuff into orbit, we sent jellyfish into space. Then, it seemed almost comically simple to come up with a science experiment. Pick an object or living thing, launch it into orbit, see what happens. But it wasn’t as easy as it seemed. For NASA to accept your proposal, you had to have a good reason for it—you couldn’t just send anything up there.
So when astronauts shepherded jellyfish polyps into space on SLS-1 June 1991, the scientists who proposed it had a very good justification for their experiment—they wanted to see what would happen when a living thing was reared exclusively in microgravity.
RR Helm at Deep Sea News dug up this gem of an experiment, writing:
When a jelly grows, it forms calcium sulfate crystals at the margin of its bell. These crystals are surrounded by a little cell pocket, coated in specialized hairs, and these pockets are equally spaced around the bell. When jellies turn, the crystals roll down with gravity to the bottom of the pocket, moving the cell hairs, which in turn send signals to neurons. In this way, jellies are able to sense up and down. All they need is gravity.
What makes this experiment significant is the fact that humans have similar structures to sense which way is up or down. Sending jellyfish polyps into space, letting them develop, and then observing them back on Earth can give us a pretty good idea of how humans born and reared in space may respond when they later set foot on a planetary body.
After the jellyfish progressed from polyps to medusae aboard the shuttle and then returned to Earth, scientists watched how they swam. It wasn’t good. Unlike jellyfish reared on Earth, the space jellies had trouble telling up from down and couldn’t move as gracefully. Those results suggest that if we humans are to spend generations traveling to another system, we’ll have to figure out how children born aboard the spaceship will acquire a taste for gravity. Otherwise, our colonization efforts could stumble before they even set foot on a planet.