According to lead author of the study, Hal Levison from the Southwest Research Institute, this timescale of how gas giants and rocky planets were formed has been problematic for scientists, especially how Jupiter and Saturn could exist in the solar system. But the details of that planet-forming process are still up for debate. Observations of young star systems show that the gas discs that form planets usually have lifetimes of only 1 to 10 million years, which means the gas giant planets in our solar system probably formed within this time frame. [Video: Best-Ever View of Exoplanet Birth].
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“Rather than creating a few such cores, (this process) produces a population of hundreds of Earth-mass objects that are inconsistent with the structure of the solar system”, astronomer Harold Levison, with the Southwest Research Institute in Boulder, Colo., writes in this week’s Nature. The original theory was that ice and dust slowly morphed into large balls, which eventually formed the nuclei of the gas giants Jupiter and Saturn.
But there was a problem with the latter idea: there wasn’t enough time before the sun’s circumstellar disk would have run out of planet-forming materials for these gas giants to form in this fashion.
“We basically produce the start of the Nice model”, Levison said.
The chances of two (2) or more giant planetesimals colliding with one another and merging together were not high enough to form massive gas giants quickly enough.
And that was just what they saw. “The growing cores need some time to fling their competitors away from the pebbles, effectively starving them”.
And that’s where the new simulation comes in. “It’s about giving gravity more time, so large embryos can bully the small ones”. According to SRI scientist Katherine Kretke, if these pebbles form too fast, this pebble accretion will lead to the formation of hundreds of icy Earths. Previous researchers relied on the core accretion model claiming that the icy and rocky core of the planet was the first to take form and then, the planet’s dimensions grew due to the interstellar dust and gas surrounding them.
Levison’s team fixed that problem by allowing more time for the pebbles to develop into planetary cores.
It all goes back to the early days of the universe, as tiny clumps of dust and ice began to form into our solar system, orbiting our infant Sunday.
There is a lot we actually do know about our solar system. It is the fifth planet of the sun and has the mass of more than 300 Earths – although, to give you some perspective, it’s just a thousandth of the size of the Sunday.
Computer simulations that researchers have made have revealed that pebbles have to get to the core of the planet at a very low speed; otherwise, the entire formation process would be ruined.
The new model solves this problem by allowing these early accumulations of pebbles to interact with and influence each other. “This paper shows hope of overcoming some of the previously identified difficulties”.
Now researchers are testing whether the pebble accretion model, or some variation of it, can explain the formation of terrestrial planets like Mars and Earth.
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“It’s a whole new way of looking at planet formation, and people are still working out exactly what it means”, said John Chambers, a planetary scientist at the Carnegie Institution of Washington.
