For years, astronomers have suspected that our solar system may have lost at least one world at some point in its 4.5-billion-year history. And now, new research suggests the moons of Jupiter and Uranus may indeed hint that our planetary neighborhood once had a third ice giant.
Evidence has shown that between 3 billion and 4 billion years ago, the solar system's largest planets likely orbited much closer to the sun (and to each other) than they do today. It's also suggested that our four giant planets — Jupiter, Uranus, Saturn and Neptune — gradually shifted into their current orbits due to a series of interactions with one another's gravity.
