# The Effects of gravity on humans and animals on a world 4x the size of Earth

I am Building a world over 4 (about 4.7) times the diameter of earth. It's made of the same elements as earth. It rotates on an axis same as earth so it has the same seasons as earth. But it rotates faster so its days also match the time of an earth day.

So I'm simply assuming it would have the same ratio of size of Earth to Earth's gravity, as to the size of this world and its gravity.

Also the scenario is that humans and other flora and fauna evolved on earth and hypothetically appeared here on this world. So what would happen to them, would the animals just be crushed? Could the plants even grow?

Also to top it all of what features would they have to evolve to live here? And how much further away from its star(exact same as the sun) would it have to be for the climate to be just right for earth conditions.

It also will take the same amount of time to orbit its star as it does for earth.

• You need to be a bit more specific. What do you mean by the 4x size - is it mass, is it radius, is it both? This is a very broad question. – JANXOL Dec 9 '20 at 18:42
• Hi CausticNickel, and welcome to Worldbuilding! As it stands, this question is both too broad and insufficiently detailed to allow a good answer. Important clarifications that will help your question get a good answer: is the increased size of this planet its diameter, its volume, or its mass? Is its density the same as Earth's? Would the animals and humans have evolved on that planet, or elsewhere and then were brought to this planet? – jdunlop Dec 9 '20 at 18:42
• Also, the effect of gravity on life is addressed in multiple other questions. – jdunlop Dec 9 '20 at 18:45

Alright, so... First a nitpick regarding the rotation. If it's supposed to have a 24 hour rotation period like the Earth, your planet needs to have the exact same angular velocity of rotation as the Earth, which is about 360 degrees per 24 hours. It cannot rotate faster, unless you mean equatorial speed, which will indeed be higher to compensate for increased diameter. I suggest to specify that part. I will follow with the assumption that the planet has 24 hour rotation period and hence same angular velocity of rotation as Earth.

Gravity

Your planet has 4.7 times the diameter of Earth, which puts it at almost 104 times the volume. Assuming that "being made of same elements as Earth" corresponds to the same density as Earth, we're looking at 104 times the mass of Earth. To give you a concept of scale, that's about 1/3rd of mass of Jupiter.

Using Earth's mass and radius as basis and knowing that we have 104 times the mass and 4.7 times the radius we get 4.7 times the gravity.

Life from Earth

With 4.7 times the gravity, you weigh 4.7 times as much as you do here. If you weigh 60kg, now you suddenly weigh 282kg, while your muscles are exactly as strong as they used to. It's exhausting at best and most defintiely harmful if you intend to experience this for an extended period. Most people would probably black out immediately, as an untrained individual is expected to go into G-LOC (G-force induced Loss Of Conscioussness) when exposed to more than 4G acceleration for a brief moment, let alone constantly. Astronauts and military jet pilots are trained to withstand these kind of forces, but only for brief moments.

I wouldn't say they'de be crushed, as you do not mention anything about increased atmospheric pressure, but they would collapse under their own weight and be unable to pump enough blood into their brain against the force of gravity.

The same would apply to animals, though I am not sure about impact on plantlife.

How far from the Sun

If the star is the same as our Sun, the habitable zone would also be the same, which means the planet would be located at roughly the same distance as Earth. And if you want to have the exact same orbital period as Earth around the exact same star as the Sun, the orbit of your planet needs to also be exactly the same.

I suppose living organism could be adapted to live there through some sort of genetic modification, though they wouldn't get a chance to naturally evolve there - if that's what you were asking - as they wouldn't be able to function on this planet before they are engineered to survive there.

For specific biological adaptations, I suggest you explore the answers to this question.

@JANXOL already made all the points. But i do want to talk a bit about how much this is not a world for Humans.

The most apperant Problem is Gravity of course. 4,7x the acceleration will kill most people rather fast. Not to mention that you could not breath at all because the Air is to dense. It is actually pretty interseting. If we assume the same Ratio of Planet mass vs Atmosphere Mass you would just die. Sure you can breath IN, but you cant exhail.

The reason being that your Lungs can only "push" around 1.1Atm of PRessure around. So if the Pressure outside would be 1.1Atm, so 10% more, you could still breath but it would be hard. Anything above that will force air into your Lungs and prevent you from breathing out.

So no, Gravity wont kill you, you will suffocate before that. Or in other terms, if you are lucky you will black out from Gravity and then suffocate.

The same is true for pretty much every Animal on Earth. Creaturs in the Oceans might survive as Water cannot be compressed, thus the Pressure is about the same. But Gravity would still kill the large ones.