Gas Giant Origins

Gas Giant Origins

Scientists have always thought that huge, gaseous planets like Jupiter and Saturn took at least a million years to form. New research, however, shows that it might not have taken that long at all. You'll hear why in this Science Update.


Giant planets in a jiffy. I'm Bob Hirshon and this is Science Update.

Astronomers have found more than a hundred planets orbiting other stars. All happen to be gas giants, similar to Jupiter and Saturn.

Now, scientists have a new model to explain exactly how this kind of planet first forms. Thomas Quinn is an astrophysicist at the University of Washington. He says scientists have long speculated that gas giants grow out of the extra dust and gas that surrounds a new star. Over millions of years, the dust collects into a rocky core, and then the gas is pulled in by the core's gravity. But Quinn and his colleagues propose a faster method.


The idea is that the gas planets form directly from the fragmentation of the gas disk that was around the forming star.

That is, the gas simply breaks up and forms individual planets. Quinn and his colleagues ran a simulation of the new model and found that it worked. What's more, it also showed that these enormous planets could form in only a few hundred years.


What we got out was a handful of Jupiter-sized planets or greater, very similar to the types of planets that we're discovering.

This faster growth process could explain why there are so many gas giants out there to discover. For the American Association for the Advancement of Science, I'm Bob Hirshon.

Making Sense of the Research

If you ever believed that science was perfect, this study should prove you wrong. For decades, astronomers had been living with a model of the formation of gas planets that didn't really make sense. The idea itself was compelling: it begins with a swirl of cosmic debris around a young star, continues as the debris collects into giant hunks of rock much larger than the earth, and finishes with gas slowly accumulating around those rocky cores, like a snowball.

The problem was, every time astronomers calculated how long this would take, they'd come up with millions of years. But in that amount of time, the heat from the star (and other stars nearby) would easily boil off and dissipate all the surrounding gas. As a result, astronomers couldn't get the math to justify the existence of planets as large as Jupiter or even Saturn.

Enter Quinn and his colleagues (Lucio Mayer, James Wadsley, and Joachim Stadel). They decided to test the alternative model you just heard about. They weren't the first people to come up with this idea, but they were the first to try it with a computer powerful enough to predict the formation of something as specific as a planet.

The fact that the model worked suggests that giant gas planets should be relatively common, since they can form relatively quickly and easily. And that matches up with the latest observations that astronomers have made. It also shows that our understanding of the universe is constantly evolving, and it's always possible that a new theory can come along that turns an old theory on its head.

Even this model is far from complete. For example, it accounts only for the formation of gas planets, and not solid planets like Earth. It also doesn't explain the existence of smaller celestial objects like asteroids and comets. So there's still much work to be done before we fully understand how solar systems like our own are born.

Now try and answer these questions:

  1. What is the main difference between the old theory of gas giant formation, and Quinn's team's model?
  2. Why was the old model unsatisfying?
  3. What obstacles make it difficult to answer the question of planetary origins?
  4. What kind of information goes into building a model like this? What factors might limit the model's accuracy or power?

For Educators

ScienceMaster offers this page of information on gas giant planets.

Explore the solar system courtesy of NASA's Jet Propulsion Lab.

In The Expanding Universe, students (grades 9-12) create a balloon model of the expanding universe and review Hubble Space Telescope measurements that are refining estimates for the age of the Universe.

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