A New Model of Gas Giant Planet Formation

Southwest Research Institute scientists used computer simulations to nail down how Jupiter and Saturn evolved in our own solar system.

It is known that gas giants like Jupiter and Saturn are so large in size that they can easily swallow our planet earth.

Scientists’ new computer model found a way for these massive wonders to form from mere collections of pebbles.

The largest planets in our solar system may have grown from the tiniest beginnings, new research suggests. The new simulation’s results finally got it right: Two rocky cores, which would end up as Jupiter and Saturn, and two icy ones, forming the cores of Uranus and Neptune.

This artist’s concept of a young solar system shows gas giants forming first, while the gas nebula is present.

However, new research reveals that these gas giants could well have come into being within the ten-million-year deadline.

Pebbles and larger chunks – called planetesimals – are related.

It was thought that rocks merge with rocks. In planetary science lingo, these are “pebbles”. Pebbles are not interacting just by gravity. When they encounter other pebbles, they clump together and take advantage of a wake in the wind of gas, like flocking birds. “That solves the meter barrier-you go directly from pebbles to 100-kilometer-sized things, nearly overnight”, Levison says.

The latest paper on the “pebble-accretion” scenario, published in the 20 August issue of Nature, describes how embryonic planets whizzing around the Sun would have nudged one another as their gravitational fields interacted.

But they wondered what would happen if instead of having pebbles coalesce from dust all at the same time, the pebbles formed at different rates.

And that was just what they saw.

“It really is a paradigm shift for how planets form”, said Levison. “The smaller guys, which become more eccentric and more inclined, get scattered out of the disk where the pebbles are”. Small dust grains can grow as they collide and stick together with static electricity. “The runt is pushed aside by its bigger siblings so that they grow, and it doesn’t”.

There is a lot we actually do know about our solar system.

The researchers’ modeling runs-which each take weeks on a cluster of five computers-typically predict one to four gas giants like Jupiter and Saturn in orbits between 5 and 15 astronomical units (AU) from the Sunday.

The 4.56-billion-year-old solar system began in a hurry.

After many decades of exploring the solar system, we still have much to learn about our closest celestial neighbours. Both of these reasons mean simulations require far more resolution elements than the outer planet models use.

“Some stories of planet formation are “avoidable” – that is, there are alternative stories – but the pebble-accretion story is in some form or other likely to be important”, David Stevenson, a planetary scientist at the California Institute of Technology in Pasadena, who was uninvolved in the study, told Space.com.