# Predicting Worlds With Lower Gravity

• Handerson Tjia
But the mountain is also weathering. The surrounding terrain was already lower.In summary, the conversation is about creating a believable and scientifically accurate world for a novel. The topic of gravity and its effects on the planet and its inhabitants is discussed, including the potential for taller trees, differences in jump height, and the impact on people from Earth. There is also mention of atmospheric differences and examples of real-life planets with similar characteristics. The conversation also touches on the possibility of continental drift, the survivability of atmospheres close to stars, and the effects of rotation on gravity. The conversation ends with a discussion on the erosion of mountains and how it could be used in the fictional world.
Handerson Tjia

So, recently I tried to write a novel. It is an ongoing project, and very far from completition. I've read so many Sci-Fi stories before, and some do not follow general physics very well. I want to make a world that is believable, but also scientificly correct. It doesn't need to be so precise, but it has to differ a little bit. I wonder if this forum can help giving some enlightenment on the subject, despite it being Sci-Fi stuff.

I may ask for some thought exercise, what would happen in a planet that has 0.92 less gravity than Earth or 9 m/s2?

I've come up with some rough estimates, such as
- Trees being slightly taller
- People from Earth jump slightly higher
- People from this planet suffer fatigue and knee injury on Earth

So, if you have other ideas on what will happen to this planet and Earth people that move to it, let me know! I might ask for rough formula to your theories, for example h = 1/g on jump height.

Please feel free to go crazy on this thread! I might need all details I can get. Thank you.

The atmosphere may be a little thinner, like living in the mountains, perhaps. Have you read any of Larry Niven's books? Neutron Star (I believe that's the name) is a collection of short stories. There are different worlds. There is a group of people called Belters in one of the stories. They live in the asteroid belt, mining the asteroids. Integral Trees is another interesting one, with low gravity.

Trees wouldn't necessarily be bigger, that has much more to do with the energy output of the sun.

There doesn't strike me as anything that would be obviously different at 92% gravity. I'd bet after only a few minutes on the surface, you wouldn't even feel a difference anymore. The planet would be about the same size as Earth.

Zenvir Singh
scottdave said:
The atmosphere may be a little thinner, like living in the mountains, perhaps.

Venus has slightly lower gravity, but much denser air.

scottdave
snorkack said:
Venus has slightly lower gravity, but much denser air.
Nice point. But is that due to the gasses which make up the atmosphere, or the gravity?

Titan also has a much thicker atmosphere than Earth and has about a sixth of the gravity.

newjerseyrunner said:
Trees wouldn't necessarily be bigger, that has much more to do with the energy output of the sun...

The surface tension of water has a much larger effect. I am fairly certain you subtract gravity. So lower gravity means the capillaries can transport water higher. Some trees break the rules. On the California coast water will condense directly out of the air. The redwoods are ridiculously huge because they bypassed the capillary limits. Some bromeliads take water out of the air and do not bother with soil at all.
Handerson Tjia said:
...

I may ask for some thought exercise, what would happen in a planet that has 0.92 less gravity than Earth or 9 m/s2?

...Please feel free to go crazy on this thread! I might need all details I can get. Thank you.

One impact of lower gravity may be continental drift. A smaller planet could have a cooler mantle/core. Without moving plates and subduction zones the mountains would have eroded and would not get replaced. Probably a boring world.

0.92g tells us very little. Earth has density 5.5 g/cm2. Uranus has surface gravity 0.89g but it also has 4x Earth diameter. A water world could have a lower density than Earth but the effect of surface gravity would be trivial in your story. There is active debate about the survivability of atmospheres close to stars. You could get around that by increasing the size of the star and moving your planet's orbit out slightly. Whether or not the planet is inside the habitable zone will have a huge impact on what sort of life would be possible.

A tidal locked binary planet would have variable gravity. The away side has higher gravity. Technically gravity on Earth is also variable because of tides. Rotation also makes the effective of gravity lower at Earth's equator. A rapidly rotating planet could have 0.92 m/s2 at the equator and 1.0m/s2 at the pole.

stefan r said:
One impact of lower gravity may be continental drift. A smaller planet could have a cooler mantle/core. Without moving plates and subduction zones the mountains would have eroded and would not get replaced. Probably a boring world.
Neither Mars nor Venus has moving plates. Both have mountains.
Though recently little liquid water. If Mars had still flowing rivers in Martian valley networks, how far would Tharsis have eroded?
Would trees have grown taller on young Mars, when the rivers flowed?

snorkack said:
Neither Mars nor Venus has moving plates. Both have mountains.
The mountains are volcanic. Poor choice of words on my part. Mars also has ancient meteor impacts.

snorkack said:
If Mars had still flowing rivers in Martian valley networks, how far would Tharsis have eroded?
Devils Tower [Bear Lodge Butte] in Wyoming is dated 41 million years. So the surrounding plains eroded at least 265 m in 42 million years. Glaciers could move a lot of material from the highest spots.

## 1. How does lower gravity affect human health?

Lower gravity can have both positive and negative effects on human health. Some studies suggest that prolonged exposure to lower levels of gravity can lead to muscle and bone loss, as well as changes in the cardiovascular system. However, there is also evidence that lower gravity can reduce the risk of developing certain conditions such as osteoporosis.

## 2. Can humans survive in a world with lower gravity?

Yes, humans can survive in a world with lower gravity. However, there may be some challenges and adaptations that need to be made in order to maintain good health. For example, exercises and training may be necessary to prevent muscle and bone loss.

## 3. Will lower gravity affect the growth and development of plants and animals?

Yes, lower gravity can have an impact on the growth and development of plants and animals. Some studies suggest that plants may grow taller and animals may have longer limbs in lower gravity environments. However, there is still much research to be done in this area to fully understand the effects.

## 4. How does lower gravity affect the environment?

Lower gravity can have a significant impact on the environment. For example, the lower force of gravity may result in different weather patterns and atmospheric conditions. It may also affect the movement of air and water, which can impact the distribution of nutrients and resources.

## 5. Can we predict what life would be like on a world with lower gravity?

While we can make educated guesses based on scientific research, it is impossible to accurately predict exactly what life would be like on a world with lower gravity. There are too many variables and unknown factors to make definitive conclusions. Further studies and experiments are needed to fully understand the potential effects of lower gravity on life.

• Sci-Fi Writing and World Building
Replies
0
Views
925
• Sci-Fi Writing and World Building
Replies
0
Views
370
• Sci-Fi Writing and World Building
Replies
6
Views
995
• Sci-Fi Writing and World Building
Replies
31
Views
2K
• Sci-Fi Writing and World Building
Replies
21
Views
1K
• Sci-Fi Writing and World Building
Replies
15
Views
1K
• Sci-Fi Writing and World Building
Replies
9
Views
2K
• Sci-Fi Writing and World Building
Replies
30
Views
2K
• Sci-Fi Writing and World Building
Replies
14
Views
2K
• Sci-Fi Writing and World Building
Replies
17
Views
4K