Twenty years ago this month, a planet appeared on the TV new program Nightline. That’s because the planet was the first world ever found orbiting another star like the Sun. And today, astronomers are still learning about this famous world.
The planets we see with our unaided eyes, such as Venus and Mars, look bright because they’re close to us. Unlike stars, they shine by reflecting the Sun’s light rather than generating their own.
That means planets in other solar systems are difficult to see, because the light they reflect is overpowered by the much stronger light of their star.
Even so, in 1995, Swiss astronomers discovered a planet orbiting the Sun-like star 51 Pegasi. They detected the planet not from its light but from its gravity: It tugged at its star, making the star move toward and away from us every four-and-a-quarter days — indicating that the alien world circled its star that rapidly. The observations suggested that the planet was a giant like Jupiter, the biggest planet i