The One Problem With Terraforming and Colonizing a Super-Earth

Question

Many people are excited with the idea of super-Earths--rocky, habitable exoplanets greater in mass, density and diameter (because I'd prefer to go the whole way than stop at the halfway point) than our Earth--being also more habitable than our Earth. That would make sense climatically, geologically and magnetically speaking.

But gravitationally speaking, I'm sorry, but I don't buy the excitement.

Anyone would know that the bigger a body, the greater the gravity, and therefore the likelier we'd end up getting crushed upon contact with either the atmosphere or the surface. You won't be seeing any spine as mighty as the Andes, the Himalayas or even the Mid-Atlantic Ridge anywhere anytime soon. On a similar note, the ocean floor will be just one uniform abyssal plain.

But somehow, somehow, one eager terraformer was not aware of any of this, and he decided to colonize this microbe-exclusive, no-oxygen super-Earth with plant, fungus and animal colonists from our Earth, colonists who had not evolved to live under either a crushing atmosphere or a crushing sea-level surface. We've tried and tried, even after we've turned blue, to reason with him, but he wouldn't listen. He insisted that he'd come up with a way to counter the gravity issue. Would such a solution exist without resorting to destructively shrinking the planet's size?

Answer 1

Depends, how high gravity do you mean? This study's summary https://arxiv.org/abs/1808.07417 for example suggests that 3-4 g might be doable for humans to train for. As for other life forms, they too should have no problem with that level of gravity. Of course, it would require adaptation, and prepare for human collonists to become fantasy dwarves rather quickly(in manner of few generations).

As far as I can tell, he needs no special solution, just normal things. There's no try, only do. Release the plant and fungal life, it'll find a way, release the animals(though animals that do well in extreme situations), and train your colonists in 2g in a spinning spacecraft, like they're hamsters.

Answer 2

Spin it faster. Really fast.

CoRot-7b for example is average Super-Earth at about 1.6 Earth radius (10k) and 8 Earth masses. It would be about 3G at the surface according to a gravity calculator I found.

Rotation doesn't counter much gravity; the rotation the Earth counters less than a tenth of a percent of Earth's gravity at 24 hrs per rotation.

However according to a centrifugal force calculator I found, at 10k radius a rotational period of 1.2 hours would counter 2 gravities.

This might be able to be a bit slower because spinning that fast is going to cause the planet to expand by an unknown amount. The expansion would be greatest at the equator and nonexistent at the poles leading to an ovoid shape.

The effect would not be equal across the planet; the -2G spin effect is at the equator, at the poles the full planetary 3G would be felt.

This brings up interesting dynamics like a 45 minute day, the difficulty of flying over the poles, the effect on migratory birds, and I don't know what the effect on atmosphere density would be across latitudes.

Answer 3

Planets, including super earths, come in all sorts of sizes. There are literally trillions of planets and moons in our galaxy alone, and it’s easy to imagine a slightly larger or denser rocky planet with 1.1g or 1.2g on which humans could survive with little adjustment needed. With rigorous training, the average human can walk around on a planet with 3 to 4 times as much gravity as what we feel on Earth, but even elite athletes will struggle to take a few steps under 5g. For reference: https://www.discovermagazine.com/the-sciences/whats-the-maximum-gravity-we-could-survive

You mention a “crushing sea level surface,” but you’re forgetting about buoyancy, which effectively negates the force of gravity. If a world is rendered uninhabitable by its crushing gravity, floating in the sea or any other body of water would allow humans or native life forms to survive. It’s likely that on a super earth with limited terrestrial life, all of the large animals will be found in the sea. The only reason why features on the sea floor might be flatter is that they feel their own weight, as there is no upward force exerted by water beneath them.

Beyond that, have you considered exoskeletons? This technology already exists. Here, it allows humans to lift heavier loads, but it could also support their bones on a planet where they weigh twice as much. These also come in handy when spacefaring explorers’ muscles and bones have atrophied as a result of life in zero g.