How the Tatooine planets survive with two suns.

It is difficult for an exoplanet to settle in a neighborhood built around two stars rather than one star. But astronomers have located many of these extraterrestrial worlds, sometimes called "Tatooine's".

In new research, scientists tackle how a planet might survive orbiting one star in a pair with a companion star located about as far away as Uranus is from the sun. That combination forms a particularly chaotic environment, one in which it's difficult for globs of material to stick together well enough to build up planets, as astronomers' primary idea of planet formation goes.

"This theory makes sense for planetary systems formed around a single star, but planet formation in binary systems is more complicated, because the companion star acts like a giant eggbeater, dynamically exciting the protoplanetary disc," study co-author Roman Rafikov, an astrophysicist at the University of Cambridge in the U.K., said in a statement.

According to the scientists, having a second star on the image increases the speed at which material globes collide, preventing them from sticking together.

"But because of the gravitational 'eggbeater' effect of the companion star in a binary system, the solid particles there collide with each other at a much higher velocity," Kedron Silsbee, a physicist at the Max Planck Institute for Extraterrestrial Physics in Germany, said in the same statement. "So when they collide, they tear each other apart."

The particular arrangement of stars and planet — two stars separated by about 20 times the distance between the sun and the Earth, with a planet orbiting one of them — the scientists analyzed wasn't chosen randomly: Rafikov and his colleagues were inspired by the nearest system to our own, called Alpha Centauri. But there's no way of going back in time to Alpha Centauri himself, so scientists turned to simulations.

These simulations resulted in scenarios where a planet was able to coexist with a pair of stars. In particular, for a planet to develop successfully in this model, the scientists discovered that the system had to start with a fairly uniform disk of rubble surrounding the stars. This disc also needed to be quite circular and the pieces of the planet, also known as planetesimals, must start at approximately 6 miles (10 kilometers) wide or more.

These combined factors slow down the interactions between pieces of a potential planet sufficient for a matter to construct itself in foreign words, scientists believe. The research could support what scientists call the flow instability model of planetesimals, which group pieces of pebbles and blocks of material surrounded by gas into larger planetesimals.

According to the statement, the scientists hope that this research can serve as a stepping stone to understanding the still-more-complicated "Tatooine" worlds, where an exoplanet orbits both the stars that make up a binary system.

The search is described in an article accepted for publication by the journal Astronomy & Astrophysics, a version of which was published on the pre-printed server arXiv.org on 23 July.