The first confirmed exoplanets were shockers. They orbit the remnant of an exploded star. And astronomers are still trying to figure out how they were born.

The star is a pulsar. It formed when the core of a massive star collapsed, causing its outer layers to blast into space. The core is heavier than the Sun, but no bigger than a city. It rotates almost 10,000 times a minute, emitting a beam of radio waves with each turn. From Earth, we see the beam pulse on and off like a lighthouse.

The pulses form an extremely accurate clock — there’s no variation in the timing of the “ticks.” Unless, that is, something else changes the pulses. And that’s what Aleksander Wolszczan and Dale Frail found in the early 1990s. They saw tiny changes in the timing of PSR 1257+12. They concluded the changes were caused by the gravitational tug of orbiting planets.

They found three planets in the system. Two are a few times heavier than Earth, while the third is close to the mass of the Moon. Others have since discovered planets around a few other pulsars.

A supernova shouldn’t leave any planets behind. So astronomers have come up with several ideas to explain pulsar planets. One says they may form from debris blown off the surface of a companion star. Another says they belonged to a companion star but were stolen by the pulsar. However they formed, they’re the first confirmed planets orbiting a star other than the Sun.

More about exoplanets tomorrow.

Script by Damond Benningfield