Only a few of the thousands of known planets in other star systems have ever been seen. Most exoplanets are discovered through their effects on their parent stars. But a system in Pegasus is a major exception. Astronomers have discovered four planets in the system – and they’ve seen all of them.

HR 8799 is about 130 light-years from Earth. The star is bigger, brighter, and heavier than the Sun. And it’s much younger – tens of millions of years, versus four and a half billion years for the Sun. And that’s one reason we can see the planets – they’re still warm from their birth, so they produce a lot of infrared light.

Another reason we can see the planets is that they’re a long way out from the star – many times the distance from Earth to the Sun – so they’re not masked by the star’s light. And the planets are giants – they’re up to 10 times the mass of Jupiter, the giant of our own solar system.

Recent observations by Webb Space Telescope suggest the planets formed in the same way as Jupiter. Blobs of rock and metal stuck together to form a heavy core. The gravity of the core then swept up huge amounts of gas.

The system might still be taking shape. A giant disk of dust surrounds the planets, and is being stirred up by their gravity. And the planets themselves may be shifting position – finding the right arrangement before this young, busy system settles down.

Script by Damond Benningfield