NASA’s Cassini-Huygens is an unmanned spacecraft sent to the planet Saturn, the fourth space probe to visit the ringed planet and the first to enter orbit. It has studied the planet and its many natural satellites since arriving there in 2004. Cassini is powered by 32.7 kg of plutonium-238 – the heat from the material’s radioactive decay is turned into electricity. Now the Cassini probe is orbiting Saturn, it is between 8.2 and 10.2 astronomical units from the Earth. It takes 68 to 84 minutes for radio signals to travel from Earth to the spacecraft, and vice versa. Click here to view the first image in this week’s funny school pictures gallery. Continue reading for a viral video compilation showing why gravity sucks.