It’s called gravity and it does loads of important jobs – it’s what makes waves move and even has an effect on the weather!
Gravity’s been around since the start of the universe.
It pulled the atoms together to make stars and planets, and keeps them in their orbits.
It also keeps the atmosphere close to the surface and your feet on the ground.
The gravitational pull of the moon’s orbit around the Earth creates the waves in our oceans too.
Here’s a crazy thing though, if you dropped something in a spacecraft – far away from the Earth’s gravitational field – you might have time to catch it!
You’ll find gravity wherever there are objects like planets but it can be stronger or weaker depending on where you are,how big the objects are and how much mass they have.
For example, if you weighed 30kg on Earth, on Mercury and Mars you’d only weigh about 11kg – just a third of what you weigh on Earth.
Jupiter would be a different matter. It’s much bigger and bigger objects have a greater gravitational pull so you’d weigh twice what you do on Earth!
And if you think that’s bad, if you stood on the Sun you’d weigh over 800kg – that’s heavier than a car!
How strong gravity is will affect the way life develops on other planets.
We don’t know for sure but it’s likely that life on planets with very strong gravity would be found very close to the ground and might have to be very tough and strong to move around.
So if we know how big a planet is, how much mass it has and what other objects it’s close too, we might be able to work out quite a bit about it!