Don't support crappy science fiction where every planet has the same gravity as Earth. Astronomers say the planets most likely to support life are ten times the size of Earth. When we finally meet aliens, they'll envy the spring in our step. Movies and other media are squandering the awesome story potential of creatures from a heavier world. Here are four theories from science fiction (and science!) about how high-gravity aliens would behave.

  • Aliens on high-gravity planets could be insectoid, says The Science of Aliens (Basic Books, 1999). One example: the Mesklinites in Mission of Gravity, a 1954 novel. They have 18 pairs of sucker-like feet, letting them grip surfaces better.
  • High-gravity aliens would be short and stocky, and have stronger muscles and bones. They'd also be more likely to live underwater, which might make it hard for them to develop much technology.
  • They would have a much harder time getting into space. The higher your gravity, the more thrust you need to achieve escape velocity. We're lucky we have such an easy time achieving orbit, but other species might not even put up satellites until much later.
  • A much higher gravity planet might not have an oxygen atmosphere that we could breathe. The high gravity would keep too much hydrogen around for free oxygen to develop.