Missing Planets

Astronomers have found planets orbiting all kinds of stars: big and small, young and old, and even dead. But they haven’t found many stars in globular clusters — tight balls of hundreds of thousands or millions of stars. In fact, they’ve confirmed only one planet in the Milky Way’s 150 globulars.

In part, that may be because it’s hard to make planets there. Globulars are the oldest residents of the Milky Way. Some date to less than a billion years after the Big Bang. So when the clusters were born, there weren’t many heavy elements for making planets. Those elements were created inside early stars, then expelled into space, where they could be incorporated into later generations of stars and planets.    

If planets tried to form in globulars, they might not have had a chance. Stars in the clusters are tightly packed. Encounters between stars might have stirred up the clouds of planet-making material. And even if planets did form, they could have been kicked out of their parent clusters by similar encounters.

On the other hand, globulars are a long way away, so perhaps they do have planets, but they’re just too hard to see.

The only known planet is a giant — heavier than Jupiter, the giant of our own solar system. It orbits a pair of dead stars. It’s likely that the planet was born elsewhere, then captured by the dead stars during a close encounter — giving them the only known planet in any globular cluster.
 

Script by Damond Benningfield