The first solar system would have had a fifth giant planet

Artistic representation of the early solar system, with the proto-Sun, newly formed planets and the circumstellar disk. Credit: NASA/JPL-Caltech/T. Pyle (SSC)

Billions of years ago, when the Sun was still a protostar that had not yet ignited, the young solar system may have contained a fifth giant planet in addition to Jupiter, Saturn, Uranus and Neptune.

This planet could have been ejected from the system once the Sun began to perform fusion in its core, blowing a cloud of dust from the circumstellar disk that initially surrounded it.

A 2005 theory known as nice model proposes that the gas giants Jupiter and Saturn and the ice giants Uranus and Neptune initially orbit much closer to the young Sun in circular orbits. These orbits were then disturbed by an unknown phenomenon which caused the four planets to migrate outwards.

Now, in an article published in the journal Naturescientists propose that the phenomenon that precipitated these migrations was a disbursement of the dust cloud that surrounded the proto-Sun once it ignited and began to drive fusion into its core.

The dust from this cloud disrupted the orbits of these planets and possibly ejected a fifth giant planet, which would then have become a rogue planet revolving around no star.

While the nice model suggests that this instability occurred over a long period of time, the composition of lunar rocks collected by Apollo astronauts shows that this process was rapid and took place over a few million years rather than the hundreds of millions of years indicated by the model.

Both nice model and the one proposed in the paper suggests the early existence of a fifth gas giant planet, although computer models indicate that today’s solar system could also have come into existence without the additional planet.

According to this latest study, the terrestrial planets of the solar system, which formed after the migration of the giant planets, could have been influenced by this early instability. For example, this phenomenon could be the reason why Mars has such a smaller mass than Earth.

“Our solar system has not always looked like it does today. During its history, the orbits of the planets have changed dramatically. But we can understand what happened. said Seth Jacobson from University of Michigan (MSU), one of the authors of the study. “All solar systems are formed in a disk of gas and dust. It is a natural byproduct of star formation. But when the Sun ignites and begins to burn its nuclear fuel, it generates sunlight, heating the (circumstellar) disk and eventually blowing it from the inside out.

Tagged: gas giants Solar System The Range

Laurel Kornfeld

Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ who enjoys writing about astronomy and planetary science. She studied Journalism at Douglass College at Rutgers University and earned a Graduate Certificate of Science from Swinburne University’s Online Astronomy Program. His writing has been published online in The Atlantic, the guest blogging section of Astronomy magazine, the UK Space Conference, the IAU General Assembly 2009 journal, The Space Reporter and various club newsletters of astronomy. She is a member of Amateur Astronomers, Inc., based in Cranford, New Jersey. Particularly interested in the outer solar system, Laurel made a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.

Arline J. Mercier