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Mercury has a mass of 3.30×1023 kg, making it the lightest planet in our Solar System. Because Mercury’s mass is quite a bit smaller than the Earth’s mass, its gravity is only about one-third of Earth’s. If you weighted 68 kg on Earth, you would only weigh 25.7 kg on Mercury.
With a mass of 4.87×1024 kg, Venus is one of lightest planets. Because Venus is similar to Earth in size and density, only a little smaller and lighter, it has similar gravity. The gravity on Venus is just almost 90% of Earth’s gravity. Although the gravity on Venus would not kill you, the toxic gases and raging temperatures would.
Earth has a mass of 5.98×1024 kg. We compare the masses of all the other planets to Earth because we are familiar with it and its gravity. For our own sakes, it is good that Earth’s mass is not significantly less or greater. If it was, then we may be crushed by Earth’s gravity or floating off into space.
Mars is the second smallest planet in our Solar System with a mass of 6.42×1023 kg. Earth is about ten times more massive than Mars is. Mars’ light mass means that it has very light gravity. In fact, the gravity on Mars is so light that the planet has almost no atmosphere, allowing us to get a clear look at its red surface.
At 1.90×1027 kg, Jupiter has the most mass of any of the planets. It would take 318 Earths to equal the mass of Jupiter. If you could stand on Jupiter, which you cannot because it has no solid surface, you would find the gravity crushing. If you weighed 68 kg on Earth, then you would weigh almost 161 kg on Jupiter.
Saturn has a mass of 5.69×1026 kg, making it the second most massive planet in the Solar System. Like Jupiter, Saturn has a low density. Despite its mass, Saturn’s gravity is only 91% of Earth’s.
Uranus has a mass of 8.68×1025 kg. Despite the fact that Uranus has a mass 14.5 times Earth’s mass, its gravity is lighter than Earth’s. If you weighed 68 kg on Earth, then you would only weigh 60.5 kg on Uranus.
A mass of 1.02×1026 kg makes Neptune the planet with the third largest mass. Although Neptune is more massive than Earth – about 17 times more massive – it is not as dense. Neptune’s gravity is also greater than Earth’s gravity. Someone who weighs 68 kg on Earth would weigh 76.5 kg on Neptune.
Astronomy Cast has episodes on all of the planets so start with Mercury and listen to all of them.