According to new research, gas giants such as Jupiter and Saturn started life as space rocks approximately a foot in circumference.

Scientists had previously struggled to understand how these large planets had formed, because existing models do not allow sufficient time for gas giants take shape, writes Brid-Aine Parnell for Forbes.

Scientists Say Huge Planets Grow From Space Pebbles

Previous model does not explain formation of giant planets

The gas discs which provide material for new planets usually only exist for 1-10 million years, which is insufficient for such large planets to come together. Researchers think that Earth took around 30 million years to form, but the process may have lasted as long as a hundred million years.

Most scientists support the core accretion model, in which a core of ice and rock formed first before gas and dust attached itself to the core. The problem with this model is that in order to attract such a large amount of gas and dust, the core would have to be 10 times as massive as Earth and form in only a few million years.

The problem with timescale means that the formation of Jupiter and Saturn cannot be adequately explained by the model, according to Dr. Hal Levison, an Institute scientist in the Southwest Research Institute (SwRI) Planetary Science Directorate and lead author of the new study, published in Nature.

“It wasn’t clear how objects like Jupiter and Saturn could exist at all,” he said.

New theory explains fast formation

One new theory is the idea that gas giants grew by accumulating space pebbles drawn by a gaseous wind, which would fit the 10-million year deadline. If the pebbles accumulated at a slow enough rate to allow the planets to interact with each other, the model can explain the formation of our Solar System.

“If the pebbles form too quickly, pebble accretion would lead to the formation of hundreds of icy Earths,” said study co-author Dr Katherine Kretke. “The growing cores need some time to fling their competitors away from the pebbles, effectively starving them. This is why only a couple of gas giants formed.”

As far as I know, this is the first model to reproduce the structure of the outer solar system, with two gas giants, two ice giants (Uranus and Neptune), and a pristine Kuiper belt ,” added Levison.