Have you ever accidentally let go of a helium balloon and watched it zip away? You might worry it's going to float all the way to the Moon! But don't worry—it turns out balloons have a "secret ceiling." A normal balloon can only reach about 32 kilometres high before it stops rising. This happens because the air high up in our atmosphere becomes very thin and light. Eventually, the balloon reaches a spot where it is just as heavy as the air around it, and it simply stops and floats there. To reach actual "outer space," you would have to go almost 1,000 kilometres high! Learn more!