Could Earth once have been a gas giant? © Getty Images

Could Earth once have been a gas giant?

Earth might once have been a gas giant, a planet mostly made up of hydrogen and helium.

The traditional view of planet formation is of a gas cloud collapsing, fragmenting and condensing into planets, with gas giants generally forming far away from the star where more volatile compounds are found.

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But, another process, called ‘tidal downsizing’, envisages larger gas clouds forming much further out from their stars. These coalesce into massive gas giants, with sizeable rocky cores, and then migrate inward towards the parent star, eventually losing their gaseous envelopes.

Although the theory is in its infancy and much of the details remain to be worked out, there is a possibility that the Earth could have formed from a gas giant in this way.


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