Gravity

If the planet's gravity turned off, and suddenly there was no force of gravity on planet Earth. This would turn out to be a pretty bad day. We depend on gravity to hold so many things down -- cars, people, furniture, pencils and papers on your desk, and so on. Everything not stuck in place would suddenly have no reason to stay down, it would start floating. But it's not just furniture and the like that would start to float. Two of the more important things held on the ground by gravity are the atmosphere and the water in the oceans, lakes and rivers. Without gravity, the air in the atmosphere has no reason to hang around, and it would immediately leap into space. This is the problem the moon has -- the moon doesn't have enough gravity to keep an atmosphere around it, so it's in a near vacuum. Without an atmosphere, any living thing would die immediately and anything liquid would boil away into space.

In other words, no one would last long if the planet didn't have gravity.

The surface gravity of the Moon is only about one fifth of that of the Earth. No wonder Apollo astronauts were able to jump so far on the Moon's surface! Prospective Mars colonists should note that they will only weigh about a third of their terrestrial weight on Mars. 

According to James Overduin, a physicist at Towson University in Maryland who specializes in gravitation, a universe without gravity would be "completely flat and featureless." Overduin explained that gravity is just another term for the curvature of space-time — how steep or shallow the fabric of the universe is in a given place (and thus how likely objects are to fall toward the source of curvature). Just as a bowling ball placed on a trampoline curves its surface, it is the presence of matter and energy that cause space-time to curve. So, if the universe can't curve (because gravity doesn't exist), then there can be no matter or energy within it. 

Earth's gravitational pull is responsible for the moon's orbit. Similarly, all planets, asteroids, and comets in our solar system orbit the sun due to this gravitational pull. The fact that celestial bodies millions of light years away orbit the sun debunks the myth of no gravity in space.

Gravity on Other Planets

Gravity differs depending on what planet we are on. This is because the planets vary in size and mass.

Mercury is the smallest planet with the least mass and the least density. The gravity on Mercury is only 38% of the gravity on earth. Considering Mercury only has a radius of 4,879 km, which is barely any larger than the Moon, the gravity is high. The high gravity is due to the high density of the planet.

Venus is similar in size to the Earth, which is why it is often called Earth’s twin. Its mass, density, and volume are all slightly less than Earth’s. This means that the gravity on Venus is slightly over 90% of the Earth’s gravity. Although you would weigh less on Earth’s twin than you would on Earth, you would not want to visit Venus because of its toxic, burning atmosphere.

Jupiter is the most massive planet in our Solar System, meaning it also has the highest gravity. If you stood on Jupiter – you cannot because it does not have a solid surface – than you would weigh two and a half times what you would on Earth.

A gas giant, Saturn is more massive than Earth, but it also has the lowest density of all the planets in the Solar System. If you were able to stand on Saturn’s surface, you would experience about 91% of the gravity you would on Earth.

Like Saturn, Uranus is massive, but has a very low density. Because of this combination, Uranus has a low gravity about 89% of the gravity that you would feel on Earth. This is very close to Venus’ gravity although Uranus is more than 14 times larger than Venus is.

Neptune is much more massive than Earth – 17 times Earth’s mass – but it is also much larger than Earth, so it has a lower density. This means that Neptune’s gravity is only slightly more than Earth’s gravity – 14% more. It would not be too uncomfortable walking on Neptune if you could walk on it, which is impossible because it does not have a solid surface.

The promise of life on Mars has intrigued people for centuries, but what would living on Mars really be like. Well, Mars has a smaller density and mass than our planet, which means that it has lower gravity. In fact, you would weigh less on Mars than you would on any other planet in our Solar System. The gravity of Mars is 38% the gravity of Earth.