A new study based on computer simulations has demonstrated that our solar system might be missing a planet. In fact, without an extra planet, it seems unlikely that our solar system could have formed at all, reports PhysOrg.com.


The startling discovery suggests that Jupiter, Saturn, Uranus and Neptune were not the only gas giant planets around during the formation of our solar system. There had to be a fifth gas giant, similar to Uranus and Neptune, orbiting some 15 times further from the sun than our planet Earth.


David Nesvorny from Colorado’s Southwest Research Institute reached this conclusion after performing about 6,000 computer simulations about the formation of the solar system, nearly all of which required the extra planet to work. Almost all of the simulations that factored in only the planets we know of in our solar system showed the four gas giants violently destroying one another. In the few simulations in which they survived, several of the rocky planets, such as Earth, were destroyed instead.


After adding the mysterious fifth planet, Nesvorny was able to greatly improve the odds of our solar system forming as we currently know it.


So the question remains: if our solar system is missing a planet, what happened to it?


The computer simulations also explain the fifth planet's fate. In most of the best-functioning simulations, the five gas giants begin tightly wound together. But soon the lighter planets of Neptune and Uranus get pushed into a further orbit by Jupiter and Saturn, and the fifth planet gets ejected from the solar system entirely after a close encounter with Jupiter.


If this is what happened, then somewhere out there, there may still be a solo gas giant, native to our solar system, floating aimlessly through space.


This scenario is backed up by recent discoveries of free-floating planets in interstellar space, likely expelled from their solar systems.


With a little luck, maybe one day we'll discover our fifth planet in the same way.

Bryan Nelson ( @@brynelson ) writes about everything from environmental problems here on Earth to big questions in space.

Did our solar system once harbor an extra planet?
A computer simulation has shown that our solar system couldn't have formed without an extra planet. But what could have happened to it?