Planet: earth like, half the radius of earth, gravity is .7g. Assuming this is possible and humans live on this planet, would it be possible to have 90% of the planets surface area be under water? Doesn't have to be all a deep ocean and it would have at least a couple main continents/islands. What about 85% and 80%?

I read something similar to this but it seemed that it was for earlier stages of evolution. Trying to see how possible human life would be with a planet like this. Thanks!

  • $\begingroup$ Is the human life Colonial or Evolutionary? $\endgroup$ Aug 30, 2019 at 16:55
  • 3
    $\begingroup$ Humans evolved in Africa. As far as the evolution of humans is concerned, the Americas, Australia and Antarctica might as well not exist. This already gets you to 10% land. $\endgroup$
    – AlexP
    Aug 30, 2019 at 17:00
  • $\begingroup$ Let me try that again... Is the human life that is on the planet the result of Colonization from another planet (perhaps Earth) or did they evolve on this little world? $\endgroup$ Aug 30, 2019 at 17:24
  • $\begingroup$ They evolved on this world! $\endgroup$ Aug 30, 2019 at 17:44

1 Answer 1


The earth we live on, with gravity 1g has 510.1 million km2 total surface area, of which Land area is 148.9 million km2. So we are already at the 71% mark.

Add some global warming, and we might reach 75-80% on this earth itself.

So, coming to your planet with gravity 0.7g. Water has a mass of its own. With lower gravity, we are going to see less cancellation of the viscous force that water exerts on itself. Also, there will be a general reduction in pressure that a column of sea water exerts on the water surrounding it.

Consequently, the sea water will be much more "freer", and the waves will have more energy than they have today. More energetic waves mean more more erosion of the rocks, so you will come to see the seas engulfing all but the hardest of rock surfaces.

Also, lower gravity means the rocks themselves may not be as hard (as they wouldn't have set as much under their own weight). So this is cause for further erosion of rocks, as they are softer.

So yes, you can expect to see 90% of planet's surface submerged.

  • 1
    $\begingroup$ This is a great explanation, thank you! $\endgroup$ Aug 30, 2019 at 17:46
  • $\begingroup$ Waves would be less erosive since the wind pushing them is much weaker, due to lower atmospheric density, you will not see powerful waves. Geologically the difference in height between continental and ocean crust will be less due to lower buoyancy forces. $\endgroup$
    – John
    Aug 31, 2019 at 13:02
  • $\begingroup$ @John I hadn't thought of this, that's an interesting POV. Can you post it as a separate answer? I think altering the composition of the atmosphere should be able to offset the loss of density, but am not sure how the complete walker cycle will change due to the change in gravity. $\endgroup$ Aug 31, 2019 at 15:50
  • $\begingroup$ What do you think 90% water planet would do to the temperature of the planet? Would it cool but simultaneously stabilize the temperature? $\endgroup$
    – Elhammo
    May 20 at 18:11

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .