Artifexian: Extrasolar Gas Giants

As I’ve mentioned before giant planets are often, wrongfully, left out of the worldbuilding process.

Even if I concede that the gas giants in our system (classical gas giants) are dull, no such concession can be made for extrasolar giant planets.

How a terrestrial planet grows and evolves is, in part, influenced by what sort of giant planets are present in a system. A system with a Hot Jupiter may host particularly wet terrestrial planets. An Eccentric Jupiter may produce significantly drier worlds.

Other classifications such as Cthonian Planets, Puffy Giants, Gas Dwarfs and Super Jupiters all influence their systems in their own unique ways.

Dear worldbuilder, it is in your interest to understand these planetary types. It will lead to a richer worldbuilding experience and undoubtably a richer setting.

Interested!? Click below.


…Edgar out

  • John H Reiher Jr

    There’s a theory that Mercury may have been a gas giant, forming before the Sun started fusing. So it could have been able to amass a substantial atmosphere that it subsequently lost when the Sun fired up and cleaned out the inner solar system of gas.

    Mercury as a failed gas giant accounts for its unusually large core, (50% of the planet’s diameter) and its iron-sulfide crust layer.

    • michael pulleine

      i wonder what mercury would look like as a gas giant?

      • I guess it would look like a gas giant and not at all like Mercury 😀

        • michael pulleine

          it would also not be named mercury as mercury was named for its grey colour!

    • I had never heard of this theory, very interesting

  • michael pulleine

    hey, mark ball! just in case your’e listening up there in you heavenly domain, surrounded by your angels and cherubs dresses in assorted sci-fi uniforms, could you please reply to my emais?

  • michael pulleine

    im sorry old profile pic, but im afraid i cant let you stay

  • Sorry could not keep quiet with the science stuff…. It seems John watched Solar Empire on Discovery Sci-Trek. The hypothesis of Mercury being a Gas giant before is less than a Theory as there is math involved that makes it very implausible:
    mean kinetic energy of a molecule is
    5/2*kT (for diatomic), or 3/2*kT (for monotomic, such as Helium). Same order of magnitude, so say KE=2kT
    KE also=1/2 mv^2, so
    2kT=1/2mv^2, or

    For hydrogen and helium this velocity will be greater than the escape velocity of either the Earth, or Mercury (in fact, the same is true on Mercury for other gases–hence the reason why Mercury has no atmosphere)
    In order for a gas to be bound before, either the escape velocity would have to have been greater then (which implies a more massive planet), or the thermal velocity would be have been lower (which implies a lower Temperature). If the planet had been more massive previously, there would be no mechanism for freeing the gas, you get the (chicken and the egg) problem of you need to get the mass down by letting the gas escape, but the gas won’t escape without getting the mass down. As for temperature, I believe that, if anything, the planets had had a higher temperature in the distant past. Therefore, I don’t see how the earth or Mercury could ever have held this gas.

    In older textbooks, you’ll find it stated that Mercury’s day is equal in length to its year, so that the planet keeps the same face toward the Sun, much as our Moon keeps the same face basically toward the Earth. (Some science fiction writers in the 1920s predicted otherwise, stating that the planet had a slow rotation and they were right!) In the mid-sixties Doppler radar observations indicated that Mercury rotates three times during two of it’s years.

    Mercury’s strange orbital-rotational “resonance ratio” is not the usual 1:1 found with other worlds. Its weird ratio is due to its high orbital eccentricity. Anybody who could live on its surface (protected by the most durable space suit you can imagine,) would observe a sky who’s behavior shoots down the dogmatic concept of clockwork geocentricism. A “Mercurial” 😉 observer would see the Sun rise but then gradually increase in size while moving toward the zenith. Then the Sun would stop, and reverse course, stop again, then move faster toward the zenith, and on to the other horizon while then decreasing in apparent size. And at the same time, the background stars would be racing by three times faster across the sky than seen from Earth.

  • Pt II – Mercury

    Mercury has an interior unlike that of any other rocky planet in our solar system and a surprisingly dynamic history, two new studies suggest.
    Using observations from NASA’s Messenger spacecraft in orbit around Mercury, researchers have found that the planet’s huge iron core is even larger than they had thought, and it’s likely overlain with a solid shell of iron and sulfur — a layered structure not known to exist on Earth, Venus or Mars.
    And there’s more: Mercury appears to have remained geologically active for a surprisingly large chunk of its evolutionary history, researchers said.

    “Many scientists expected Mercury, being a small planet only slightly larger than the moon, to have cooled off not long after it formed and to be essentially ‘dead’ for most of its evolution,But it appears that Mercury had an active middle age.

  • michael pulleine

    @Marquoose:disqus any idea when my story starter will be put up? i didnt get a reply from you when i sent the email for the picture to go with it.

    • Wading through a jungle of emails today. There should be a reply in your inbox right now, and your starting point is scheduled for April 19th.