‘Star Wars’ planet with two suns: a step towards Luke Skywalker’s Tatooine

A would-be Jedi waits for Kepler in a galaxy far, far away.

It’s one of the most famous and evocative images in cinematic history – Luke Skywalker gazing out at the twin suns of Tatooine as they set, in the original Star Wars movie, A New Hope.

Such a view would be unlikely in real life, or so we thought. A discovery announced in Science today, regarding findings by the Kepler mission, changes everything.

Science fiction, science fact

Throughout science fiction, stories abound of planets orbiting multiple suns – what better way to make an otherwise “Earth-like” planet seem truly alien?

But do such planets actually exist?

Following recent announcements at the Extreme Solar Systems II conference in the USA, the number of confirmed exoplanets has leapt to 677.

Of these, only a handful have been discovered orbiting around close binary stars.

In fact, such “circumbinary” planets have only been confirmed in four stellar systems, none of which even vaguely resembles the two “sun-like” stars we’re familiar with from Star Wars.

Circumbinary planets

So what is a “circumbinary” planet? Why are they unusual and exciting?

With such planets, the two stars in question orbit very close to one another, with the planet moving further out, orbiting both stars at once (technically, the planet and both stars actually orbit their common centre-of-gravity, the barycentre).

There are two main reasons why so few circumbinary planets are known.

Firstly, such planets are simply much harder to detect than planets orbiting single stars. In fact, the main radial velocity surveys searching for planets around other stars (responsible for the discovery of the great majority of exoplanets we know to date) specifically avoid such close binary star systems, such are the difficulties involved in finding planets within them using that technique.

Secondly, it might be that there really are fewer planets in close binary star systems than there are around single stars.

Indeed, a number of scientists have suggested it might be significantly more challenging to form planets around such close binary star systems than around single stars (or those that are a component within a wide binary star system).

Four circumbinary systems unlike our own

The four previously known circumbinary exoplanets are much more massive than Jupiter, and orbit at great distances from stars very different to our Sun.

NASA/JPL-Caltech