From the July 2010 issue

With many new planet discoveries being hot Jupiters, is it possible that Mercury is the leftover core of a gas giant?

Patrick Clough, Wichita, Kansas
By | Published: July 26, 2010 | Last updated on May 18, 2023
Hot Jupiter
Many of the known extrasolar planets are “hot Jupiters,” gas giants that orbit very close to their host suns.
NASA/Greg Bacon (STScI/AVL)

Mercury is not a leftover core of a gas giant planet. Although extrasolar systems have revised the planet formation rulebook, we still think gas giants form far from their stars, about as far as Jupiter is from ours.