In 1991, NASA sent over 2,000 jellyfish into space to test how microgravity affects their development and sense of balance.

The Spacelab Life Sciences (SLS-1) mission launched on June 5, 1991, aboard the Space Shuttle Columbia (STS-40). Led by Dr. Dorothy Spangenberg of the Eastern Virginia Medical School, the experiment involved 2,478 jellyfish polyps housed in flasks and bags. By the end of the nine-day mission, the population had multiplied to over 60,000 individuals through asexual reproduction.Jellyfish were chosen because their gravity-sensing organs, called rhopalia, contain calcium sulfate crystals known as statoliths. These crystals sit in a pocket of hair cells and shift when the jellyfish moves, telling the creature which way is down. This biological mechanism is remarkably similar to the otoliths found in the human vestibular system, which controls our sense of balance.When the space-bred jellyfish returned to Earth, researchers observed significant motor dysfunction. Although the jellyfish appeared physically normal, they exhibited synchronized swimming difficulties and constant vertigo. Their hair cells had developed, but the neural pathways required to interpret gravity signals never formed correctly in a weightless environment.This study remains a cornerstone of space biology because it suggests that gravity is a critical 'environmental cue' for the development of nervous systems. If humans were born in space, they might suffer from similar permanent vestibular issues. This would make it nearly impossible for space-born generations to ever physically adapt to life on Earth.