A high gravity rocky planet is a planet with breathable atmosphere (after terraforming), with accessible ground and with a gravity over 1.75 times stronger then Earth. In majority of cases, the planet is a Super-Earth, but in some particular cases, it can be smaller then Earth. All human activities will be different there from what we see on an Earth - like planet.
Frequency[]
Usually, if gravity is higher, the atmosphere must also be denser, up to a limit, where the planet becomes a gas giant. However, it is possible that a large enough planet exists without too much air circling it. If we take a gas giant (like Neptune) very close (0.05 AU) to the Sun, its atmosphere will be slowly blown away. Then, if at some point we take the planet back to its orbit, it will be far smaller, because almost only the rocky core has survived. Another way of forming a high gravity planet is by colliding a few smaller planets very close to the hosting sun (for example, by colliding 4 Earths at 1/2 the orbit of Mercury). If the angle and speed are correct, it is possible to blow away much of the crust, while the heavy cores will merge. Finally, a third possibility to find a high gravity - low radius planet, is around White dwarfs, Neutron stars and Black holes. The nebula resulting from a supernova can sometimes be just enough to create a few small planets, only that they will have a different composition, with higher amounts of heavy elements. The ultraviolet and X radiation will blow away water and atmosphere from the planet. In all cases, it is required that the planet has moved back to somewhere closer to Habitable Zone.
As seen here, there are many ways habitable high gravity planets can be formed. And also, by terraforming, some small gas giants can become high gravity rocky planets. Also, many Super Earths can be transferred into this category once the excess of atmosphere is removed.
Since random chance affects atmospheric density, as evidenced by the differences in atmospheric density between worlds with similar gravity, some high gravity habitable planets may be naturally formed.
Terraforming[]
It all depends on major conditions found on the target planet.
- A gas giant or a super Earth can become a high gravity rocky planet once the excess of air is removed. The process requires technology beyond our current achievements.
- Native high gravity rocky planets might be hard to terraform. If the planet's radius is similar to Earth but its gravity is over twice as high, it means that the planet contains high amounts of heavy elements. This is good news for miners and industrial corporations, but bad news for biologists. Heavy elements are usually associated with toxins. Certainly, it will be a hard life on a planet with lead, arsenic or cadmium in mostly all the rocks. Natural mitigation could come in the form of higher gravity causing stronger differentiation, collecting almost all heavy metals into the planetary core. Also, some Peruvian villages are already inhabited by genetically arsenic resistant people and some Russian families from western Siberia are genetically resistant to mercury. These genes could be transferred to many colonists by mild genetic engineering.
- Some heavy gravity planets may be more easy to terraform. A good example would be a planet with a radius twice that of Earth, with similar internal composition, but with nearly the same atmospheric pressure.
Environment[]
A high gravity will have strong effects on geography and biology.
Contrary to popular belief, the gravity on super-earth planet is not too much for humans. The formula for calculating gravity is ☀SG=M/R^2. This would mean:
| Name | Mass | Radius | Surface gravity |
|---|---|---|---|
| Gliese 581g | 2.6 | 1.4 | 1.33 |
| Gliese 581d | 6.9 | 2.2 | 1.43 |
| Gliese 667Cc | 4.9 | 1.9 | 1.36 |
| Kepler 22b | 6.4 | 2.1 | 1.45 |
| HD40307g | 8.2 | 2.4 | 1.42 |
| HD85512b | 4.0 | 1.7 | 1.38 |
| Gliese 163c | 8.0 | 2.4 | 1.39 |
| Hypothetical Planet | 8.0 | 2.83 | 1.00 |
The hypothetical planet is only there as an example of what a super-earth planet with earth-like gravity would be like. If humanity manages to colonize a super-earth, they would find themselves with more resources, and more room, but with weak enough gravity to take off into space. This would be immensely profitable for humanity and should be high on the priority list.
Geography[]
Erosion will be stronger on a planet with higher gravity on Earth. Most super-earths have a gravity of 40% more than Earth, but that can make a big difference. Mountains will be flatter as rivers flow faster. Plains and hills will be more common.
Also deep canyon-valleys and gorges will be very common, as water flows faster. If water is not present prior to being terraformed, valleys and canyons will soon appear after a few hundreds of years. These changes are quite slight, but they are worth noting.
Mineral resources will be more common, which will be useful for miners. Plus, the larger area means that there will be more deposits ready to dig up.
Biology[]
On a high-gravity world, trees will be smaller and grow closer to the ground. Humans will be built with a sturdier frame, and may be shorter but stronger. Provided that the gravity is near 50%. Realistically, the gravity will only be slightly stronger, so biology might not change as much.
Human life[]
Technology[]
With more ores and room to build, technology will increase faster than it would on an Earth-sized planet. A problem may be transportation, as a super-earth is extremely large and the extra gravity may require more fuel to transport goods. Buildings will be built stronger than they would on an earth-sized planet depending on the gravity. Overall technological advancement will be very promising
Demography[]
Super-Earths will be rich in ore and will focus on mining and exporting raw goods which the rest of humanity will need, given their rapid expansion. They will be extremely wealthy similarly to the Middle East which got rich selling and refining oil. Refinement of the ore and manufacturing may be done on a moon or a space station as the high gravity makes it difficult to manufacture.
Politics[]
A super-earth government will be extremely wealthy to say the least. A good present-day example we can look at is the Middle East, specifically the United Arab Emirates. They have good natural resources, and have a great cityscape, but face many building challenges just like how builders on a super-earth.