If you throw a ball, gravity pulls it back to the ground. But what if you could throw it at 17,500 miles per hour? At that speed, something amazing happens. The ball falls toward Earth, but Earth's surface curves away at the same rate. The ball keeps falling but never lands. That is what an orbit is. On October 4, 1957, the Soviet Union launched Sputnik into orbit around Earth. It was the first artificial object to circle the planet. Sputnik traveled at about 18,000 miles per hour. It completed one full orbit every 96 minutes. The satellite carried a radio transmitter that sent out a steady beep. Scientists around the world tracked the signal. Sputnik did not carry instruments for studying space. Its main purpose was to prove that humans could put something into orbit. The momentum from the powerful rocket gave Sputnik enough speed to stay up. Gravity still pulled on it, but its speed kept it falling around Earth instead of into it. After three months, Sputnik slowed down from friction with the thin upper atmosphere. It fell back to Earth and burned up. Today, over 7,000 active satellites orbit our planet.