Our young solar system may have had another huge planet that got knocked into deep space by Jupiter, reports Wired. Astronomers at the Southwest Research Institute in Texas arrived at this "Jumping Jupiter" theory because computer simulations can't figure out how our modern solar system emerged as is from that violent era when planets were ramming into each other. Adding a big (now-missing) planet into the mix—one on par with Jupiter, Neptune, Uranus, and Saturn—makes the equations work.
“The possibility that the solar system had more than four giant planets initially, and ejected some, appears to be conceivable in view of the recent discovery of a large number of free-floating planets in interstellar space, indicating the planet ejection process could be a common occurrence,” the researchers say. And it's a good thing, because if Jupiter hadn't given that planet the heave-ho, Mars probably would have slammed into Earth with catastrophic consequences, adds the Houston Chronicle. Aww. Now maybe Pluto won't feel so bad about getting kicked out of the club.