Select your localized edition:

Close ×

More Ways to Connect

Discover one of our 28 local entrepreneurial communities »

Be the first to know as we launch in new countries and markets around the globe.

Interested in bringing MIT Technology Review to your local market?

MIT Technology ReviewMIT Technology Review - logo

 

Unsupported browser: Your browser does not meet modern web standards. See how it scores »

Tatooine is the desert-like home planet of Luke Skywalker in the Star Wars movies. Famously, it orbits a binary star system so that two suns rise above the horizon each morning.

Tatooine is a work of fiction. But in recent years astronomers have found a number of real Tatooine-like exoplanets that orbit binary star systems–for example Kepler 16b, 34b and 35b

But as Sijme-Jan Paardekooper at the University of Cambridge,UK, and a few pals point out: “The existence of planets in these systems baffes planet formation theory.”

And that raises an interesting problem: how did these planets form?

Today, Paardekooper and co provide an answer. These guys simulate planet formation in a binary system at the distance these planets orbit–for 16b that’s just 0.7 AU, about the same distance as Venus from the Sun.

Previous studies have shown that the changing gravitational forces in a binary system stir up any cloud of gas and dust, ensuring a high encounter velocity between rocks. That would make it difficult for them to aggregate and stick together.

However, some astrophysicists have suggested that gas drag–the natural viscosity of gas clouds–might dampen this effect, making it possible for Tatooine-like planets to form after all.

Paardekooper and co put this theory firmly to the sword. They say their simulations show numerous perturbations that gas drag cannot prevent. “This makes the current location of the planets Kepler 16b, 34b and 35b very hostile for planetesimal accretion,” they say. 

Instead, the most likely way Tatooine-like planets form is much further away from their suns where gravitational conditions are much calmer. These planets must then have migrated to their current position over many millions of years, probably due to the dynamics of gas clouds which are known to generate pressure gradients that force planets inwards. 

Paardekooper and co make an interesting prediction, however. They say that whatever the migration mechanism of these planets, they lie at the same distance as what must have been the inner edge of their parent gas clouds. So they are about as close to their suns as is theoretically possible with this mechanism.

The implication is that we’re not likely to find exoplanets closer than this around binary stars. 

Interestingly, this distance is about the same as the habitable zone, at least for 16b. This lies at the outer edge of the zone and is thought to be a gas giant with a surface temperature of about -70 degrees C. That means its exomoons, if it has any, could be interesting. 

And if Tatooine-like planets stars tend to accumulate at this distance, perhaps the possibility of alien life forms watching twin suns rise on their home planet isn’t so unlikely after all. 

Ref: arxiv.org/abs/1206.3484: How Not To Build Tatooine: The Difficulty Of In Situ Formation of Circumbinary Planets Kepler 16b, Kepler 34b and Kepler 35b

0 comments about this story. Start the discussion »

Tagged: Materials

Reprints and Permissions | Send feedback to the editor

From the Archives

Close

Introducing MIT Technology Review Insider.

Already a Magazine subscriber?

You're automatically an Insider. It's easy to activate or upgrade your account.

Activate Your Account

Become an Insider

It's the new way to subscribe. Get even more of the tech news, research, and discoveries you crave.

Sign Up

Learn More

Find out why MIT Technology Review Insider is for you and explore your options.

Show Me
×

A Place of Inspiration

Understand the technologies that are changing business and driving the new global economy.

September 23-25, 2014
Register »