Planets Began As Tiny Space Pebbles

The genesis of a planet is a long-held mystery in the astronomical repertoire of mysterious tales of the universe. Recently, scientists reasoned out that gas giants like Jupiter and Saturn are formed from little space rocks, pebbles no more than a foot in circumference.


Until recently the formation process these planets was largely unknown to scientists because contemporary planetary models lacked the requisite time believed to be necessary for massive gas giants like Jupiter and Saturn to grow.

Consider the fact that the Earth probably took only thirty million years to form, despite the upper limit of its potentially having taken up to one hundred million years. The question begged, then, is how did Jupiter and Saturn form so quickly?


The theory among contemporary scientists is known as the accretion model. Put simply, it holds that the gas giants started as a planet-sized core of ice and rock, then grew as stellar gas and dust from the disc gravitated inwards, enveloping the rocky core in gas for the remainder of the planet’s life. However, this leaves us with the problem of how said hard core first came to be. In order to accrete the amount of gas and dust we’re looking at, the core would have to be ten times the mass of Earth.

Although the theory of accretion can explain how planets of the same order as Earth form, they don’t satisfactorily explain how planets of the magnitude of Jupiter and Saturn snowball.

“The timescale problem has been sticking in our throats for some time,” explained Dr. Hal Levison, an Institute scientist in the Southwest Research Institute (SwRI). He’’s also Planetary Science Directorate and lead author of the new study recently published in Nature.

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


However, new research reveals that these gas giants could well have come into being within the ten-million-year deadline. By channeling small planetary pebbles with the flow of accumulating gas, or rather the headwind such a flow would create, the rocky bits would be propelled inwards at a significantly faster rate.

So long as these pebbles gather slow enough to provide enough time for the gravitational wells of the planets to interact with one another, this model has a high degree of correspondence with our Solar System’s necessary timeline.

“If the pebbles form too quickly, pebble accretion would lead to the formation of hundreds of icy Earths,” warned co-author Dr Katherine Kretke, also from SwRI. “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.”

Levison added, “[a]s far as [he] knows, 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.”