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Could Humans Colonize A Planet With Stronger Gravity?

super earth gravity

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Could Humans Colonize A Planet With Stronger Gravity?

With the recent explosion of extrasolar planet discoveries, some relatively nearby, astronomers and space enthusiasts wonder how habitable some of these planets would be for humans. Just don’t forget about gravity…

With the recent explosion of extrasolar planet discoveries, some relatively nearby, astronomers and space enthusiasts wonder how habitable some of these planets would be for humans.

The Goldilocks Zone is often referenced (an area around a planet’s host star which could be ‘just right’ for liquid water to exist) when it comes to habitability. What’s not mentioned as often, however, is the planet’s gravity.

With many descriptions of these planets including words like “super-Earth”, it’s hard not to wonder if the gravity is also ‘super’ and how habitable these planets could be for us.

What Is A Super-Earth?

Super-Earth planets are planets with more mass than our own, but less than that of a gas giant. Astronomers classify a gas giant as a planet with at least 10x Earth’s mass. Don’t let the name fool you, however. A super-Earth planet could very easily be a gas planet too. These smaller gas planets are referred to as “gas dwarf planets” and are thought to be more common the closer a planet is to the 10x gas giant threshold.

A rocky super-Earth planet is one that has a solid surface, like Earth, but has a larger mass and/or radius. These types of planets are incredibly interesting to astronomers because if they lie within their stars Goldilocks zone, the greater the chance is that they could be habitable.

What About Gravity?

It’s a tricky question because planets that are larger than Earth in size may not be as dense. If a planet is less dense, it will result in a weaker gravitational pull on the surface.

gravity radius super earthThe question becomes even more complicated because the gravitational force felt on the surface of a planet is proportional to the planet’s mass divided by its radius squared.

This means that a planet with twice the radius (size) of Earth, yet similar in density (mass), would only have twice as strong gravity at its surface compared to Earth, despite having 8x Earth’s total mass.

To put it another way, a planet twice as massive as Earth would have the same surface gravity as Earth, as long as it’s radius is also proportionally larger — 4x the mass with 2x the radius, or 16x the mass and 4x the radius. g = G*M/R²

How Much Gravity Can Humans Handle?

Humans are a very adaptable species. We do have our limits though. According to NASA’s Ames Research Center’s expert on humans in space, a person has survived 2x Earth’s gravity for 24 straight hours without ill effects. They go on to claim that it is theoretically possible for a human to adapt to a gravity environment that is between 2x and 3x that of the Earth. However, they say that at 4 times Earth’s gravity (4G) or above, human physiology cannot maintain sufficient blood-flow to the brain.

In the future, it may be possible to break the 4G limit with enhancements in genetic manipulation and extremely strong mechanical replacement organs to keep our body’s systems running, but that technology is a long way off.

References:
The Astrophysical Journal 656 (1): 545–551. arXiv:astro-ph/0610122
National Science Foundation. September 29, 2010.
“The quest for very low-mass planets”, M Mayor, S Udry – Physica Scripta, 2008 Pg. 20 (PDF)

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5 Comments

5 Comments

  1. Daniel Yang

    June 1, 2015 at 1:01 am

    Relative to time on Earth, would the human on a 2x planet live longer, or would the 2x cause earlier death from the wear and tear? Time would be passing slower on the 2x planet.

    • Mark

      March 3, 2017 at 12:59 am

      Time would not pass significantly slower; gravitational time dilatation requires EXTREME gravity.

      I would expect early settlers would see a higher rate of heart attacks and the like. Of course nobody knows until we try, but the article mentions that NASA has tried this for 24 hours. We don’t know what we’ll see happen after a week, a month, a year, or even a decade. You’d imagine that those that survive a decade will be well suited to the environment and more likely to produce children with a high survival rate, but we won’t really know until we test, and it’s hard to imagine a test environment we could or even should build in the near future. The first might be something like an O’Neill cylinder spun up to simulate higher than Earth gravity, but you’d imagine the first several technical achievements of that magnitude would be used simulating Earth itself, trying to build ideal sustainable biomes, and not on experimenting on the survivability of theoretical potential colony worlds.

  2. Damia

    January 4, 2016 at 9:31 am

    Hello! I’m sorry, I’m fairly interested in physics but I can never get around to understanding the more complex concepts, especially the ones relating to the cosmos. I have heard though, from what I understand of it is that the gravity of of a planet also depends on its spin along its axis? If this is true, can anybody elaborate on this, please?

    • notneiltyson

      October 30, 2016 at 5:08 pm

      A planet or any other celestial body’s spin on it’s *axis* doesn’t affect gravity, however, it’s spin does. That’s how artificial gravity can be created although, technically, it isn’t gravity since the effects arise from centrifugal force. You ever spun a bag around with you hands and the contents stay inside even when it’s upside down? It’s kinda like that, but that’s centripetal force.

  3. Royal May

    January 9, 2017 at 6:06 pm

    @Damia the length of time on the planet is related to how fast it spins and how long it takes to orbit its sun if it has 24hr days like we do but orbits slower then those native to it would technically live longer than us.

    @Damia I believe that the spin on its axis corresponds to how long the days are thus the faster it spins the stronger the gravity, though i may be wrong on all of this, its what I’ve either figured out by myself or have been taught.

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