# Is a 1g super-Earth possible? **URL:** \ **Category:** Factual Questions\ **Created:** [May 1, 2013, 5:12pm UTC](https://boards.straightdope.com/t/is-a-1g-super-earth-possible/657222 "2013-05-01T17:12:03Z")\ **Posts on this page:** 8\ **Page:** 2
**Author:** ![Keeve](https://avatars.discourse-cdn.com/v4/letter/k/f07891/32.png) [@Keeve](https://boards.straightdope.com/u/Keeve)\ **Post date:** [May 2, 2013, 10:00am UTC](https://boards.straightdope.com/t/is-a-1g-super-earth-possible/657222/21 "2013-05-02T10:00:49Z")
> [@coremelt](#): > > Could invertebrates eventually evolve on a 10G planet or is there some physical limit that would prevent skeletons and muscles being sufficiently strong? Strong skeletons are much less important for small creatures. A 10G planet could have intelligent life that is insect-sized. ---
**Author:** ![coremelt](https://avatars.discourse-cdn.com/v4/letter/c/4491bb/32.png) [@coremelt](https://boards.straightdope.com/u/coremelt)\ **Post date:** [May 2, 2013, 10:41am UTC](https://boards.straightdope.com/t/is-a-1g-super-earth-possible/657222/22 "2013-05-02T10:41:59Z")
> [@Keeve](#): > > Strong skeletons are much less important for small creatures. A 10G planet could have intelligent life that is insect-sized. Well certainly we could get much smaller but I doubt insect sized. Apparently the smallest adult human ever recorded is 2.1 KG (!!!) at age 17. > **[Lucía Zárate](https://en.wikipedia.org/wiki/Lucia_Zarate)** > > Lucía Zárate (January 2, 1864 – January 15, 1890) was a Mexican entertainer with dwarfism who performed in sideshows. Zárate is the first person to have been identified with Majewski osteodysplastic primordial dwarfism type II. She was entered into the Guinness World Records as the "lightest recorded adult", weighing 4.7 pounds (2.1 kg) at the age of 17. > She was born in Veracruz, Mexico, and settled on the Agostadero, (later Cempoala), Veracruz. According to an 1894 article in Strand Magazine, Z... Its not recorded if she was or normal intelligence or was mentally retarded in any way. How small could our brain case be and still allow human intelligence? ---
**Author:** ![Quercus](https://avatars.discourse-cdn.com/v4/letter/q/7ab992/32.png) [@Quercus](https://boards.straightdope.com/u/Quercus)\ **Post date:** [May 2, 2013, 1:05pm UTC](https://boards.straightdope.com/t/is-a-1g-super-earth-possible/657222/23 "2013-05-02T13:05:18Z")
> [@Drum\_God](#): > > Along the same lines, is it possible to have a planet that is 100% (or reasonably close to 100%) liquid water? I’m imagining an Earth-sized glob of water floating in space. I suspect, though haven’t actually done any math, that it’s going to be difficult to maintain a planet-sized blob of liquid water. It’s a pretty delicate energy balance to keep the whole mass’s temperature above freezing, but well below boiling. Note that a) the Earth gets some heat from internal radioactive decay, and b) even the Earth isn’t above freezing everywhere. Once the poles freeze, the ice reflects a lot more light/heat so it gets even colder, making more ice… On the other hand, lots of solar radiation will tend to blow off the atmosphere (of water vapor), which as water would be continually evaporating, eventually the whole planet would go off into space as gas. ---
**Author:** ![MikeS](https://avatars.discourse-cdn.com/v4/letter/m/919ad9/32.png) [@MikeS](https://boards.straightdope.com/u/MikeS)\ **Post date:** [May 2, 2013, 5:32pm UTC](https://boards.straightdope.com/t/is-a-1g-super-earth-possible/657222/24 "2013-05-02T17:32:25Z")
> [@Drum\_God](#): > > Along the same lines, is it possible to have a planet that is 100% (or reasonably close to 100%) liquid water? I’m imagining an Earth-sized glob of water floating in space. From two months ago: [What would happen if the earth was made entirely of water?](http://boards.straightdope.com/sdmb/showthread.php?t=683894) ---
**Author:** ![Skammer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/skammer/32/143_2.png) [@Skammer](https://boards.straightdope.com/u/Skammer)\ **Post date:** [May 2, 2013, 8:51pm UTC](https://boards.straightdope.com/t/is-a-1g-super-earth-possible/657222/25 "2013-05-02T20:51:24Z")
> [@coremelt](#): > > Its not recorded if she was or normal intelligence or was mentally retarded in any way. How small could our brain case be and still allow human intelligence? According to that Wikipedia article, she was “healthy and intelligent, [and] able to speak some English along with her native Spanish.” ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [May 2, 2013, 10:47pm UTC](https://boards.straightdope.com/t/is-a-1g-super-earth-possible/657222/26 "2013-05-02T22:47:19Z")
Are there materials less dense than iron capable of generating a magnetic field as powerful as the Earth’s? And don’t forget that the Earth is kept warm in part due to radioactive decay of heavy elements, which tend to decay to iron. ---
**Author:** ![Michael63129](https://avatars.discourse-cdn.com/v4/letter/m/3da27b/32.png) [@Michael63129](https://boards.straightdope.com/u/Michael63129)\ **Post date:** [May 3, 2013, 12:50am UTC](https://boards.straightdope.com/t/is-a-1g-super-earth-possible/657222/27 "2013-05-03T00:50:20Z")
> [@Quercus](#): > > I suspect, though haven’t actually done any math, that it’s going to be difficult to maintain a planet-sized blob of liquid water. > It’s a pretty delicate energy balance to keep the whole mass’s temperature above freezing, but well below boiling. Note that a) the Earth gets some heat from internal radioactive decay, and b) even the Earth isn’t above freezing everywhere. > > Once the poles freeze, the ice reflects a lot more light/heat so it gets even colder, making more ice… Isn’t the same true of Earth though, which has even gone off in the cold direction [before](http://www.snowballearth.org/what.html)? Internal heat is also insignificant compared to solar radiation ([0.3 percent](http://en.wikipedia.org/wiki/Geothermal_gradient#Heat_flow), about twice the energy used by humans). That said, most of a water planet would consist of forms of ice that occur at [high pressures](http://www.google.com/imgres?imgurl=http://ergodic.ugr.es/termo/lecciones/phase.gif&imgrefurl=http://ergodic.ugr.es/termo/lecciones/water1.html&h=403&w=500&sz=18&tbnid=fOh19xO7V9tMfM:&tbnh=89&tbnw=110&zoom=1&usg=__YSE0jX-PRKbbjh7GyNWAzjqWOC0=&docid=95lygvIRp9zR1M&sa=X&ei=XwiDUZeELbOQ0QH6mYGIBQ&ved=0CDMQ9QEwAA&dur=946), even at temperatures well above the boiling point at normal atmospheric pressure (the pressure at the center of the Earth is about 360 GPa, which will “freeze” water into Ice X even at 800 K). > [@](#): > > On the other hand, lots of solar radiation will tend to blow off the atmosphere (of water vapor), which as water would be continually evaporating, eventually the whole planet would go off into space as gas. [This article](http://www.space.com/11187-earth-magnetic-field-solar-wind.html) says that “eventually” is such a long time that it wouldn’t be a factor on average solar lifetime time scales, assuming the star is similar to the Sun. In fact, according to it, even Mars should have lost only 30 cm of water over the past 3.5 billion years (possibly higher in the first billion years when the Sun was more active), and the Earth’s magnetic field doesn’t reduce the loss rate (note that Venus doesn’t have a magnetic field either and receives twice as much solar radiation, yet hasn’t lost its atmosphere). ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [May 3, 2013, 5:37am UTC](https://boards.straightdope.com/t/is-a-1g-super-earth-possible/657222/28 "2013-05-03T05:37:40Z")
> [@](#): > > Are there materials less dense than iron capable of generating a magnetic field as powerful as the Earth’s? And don’t forget that the Earth is kept warm in part due to radioactive decay of heavy elements, which tend to decay to iron. Sure, hydrogen plasma can generate a magnetic field, too-- That’s how the Sun does it. All you need for a dynamo is a conductive fluid, not ferromagnetism. And most radioactive decay chains end at an isotope of lead, not iron. Iron is the lowest energy state, but you don’t continue decaying until you reach the minimum, just until you reach something stable. The iron in the Earth’s core has mostly been iron from before the time of the planet’s formation, and was never anything heavier. [Previous page](https://boards.straightdope.com/t/is-a-1g-super-earth-possible/657222.md?page=1)