Planets with two suns

Luke Skywalker gazing pensively at the two suns setting over the desert planet Tatooine: an iconic, albeit fictional, scene from the Star Wars movies. Could this be a reality though? Using simulations, astrophysicist Elke Pilat-Lohinger is investigating how Earth-like planets can form in double-star systems.

Nature and Technology

by Thomas Zauner

October 19, 2026

Humanity has been wondering for a long time whether there is life out there in space – or perhaps even a second Earth. For just a little over 30 years we have known with certainty that planets – so-called exoplanets – actually exist around stars other than the Sun. Meanwhile, more than 6,000 such exoplanets have been discovered.

Astrophysicist Elke Pilat-Lohinger has been working in the field of extrasolar planet research since 1999. “Even as a child I knew that I wanted to be in astronomy,” she explains. Now a senior scientist at the Institute of Astrophysics at the University of Vienna she doesn't gaze through a telescope, but uses computer simulations to understand how planetary systems form and whether they are stable in the long term – especially in binary star systems.

“Whereas probably one-third to one-half of all stars occur as binary star systems, we have so far found exoplanets in just a relatively small number of them,” notes Pilat-Lohinger. “So the question is whether our observational methods are inadequate or whether it is simply more difficult for planets to form in binary star systems. The latter would have major implications for how many exoplanets actually exist.”

With her colleague Maximilian Zimmermann, Pilat-Lohinger is working on her current FWF-funded project “Planetary architecture in habitable zones of star systems”. The project is intended to improve simulations of exoplanet formation in binary star systems.

Planetary Architecture in Stellar Systems

The project investigates the formation of Earth-like planets using modern computer simulations. It explores how different stellar systems influence the frequency of collisions and the subsequent arrangement of the planets. The goal is to gain new insights into the formation of exoplanets.

Simulation of a protoplanetary disk in a binary star system over 10 million years. © Elke Pilat-Lohinger, Maximilian Zimmermann

Simulations using supercomputers

“A star forms from gas and dust that gradually cluster together under the influence of gravity. Around the star, a so-called protoplanetary disk forms from the remaining loose material, which orbits the star. In this disk, planets can materialize,” explains Pilat-Lohinger. “The biggest challenge in a simulation of this process is the sheer number of objects in the disk.”

During the first approximately ten million years of planetary formation, gas giants form by accumulating gas from the protoplanetary disk. Smaller terrestrial – i.e. Earth-like –exoplanets with solid surfaces then form from the planetesimals and protoplanets that have formed in the meantime. Planetesimals are objects ranging in size from hundreds of meters to hundreds of kilometers, while protoplanets are several thousand kilometers in size.

All these objects attract one another through their gravity, resulting in calculations of enormous complexity for a realistic simulation of such a protoplanetary disk containing thousands of objects. These calculations can only be done by supercomputers.

“To simplify the simulation of the formation of the terrestrial planets, it was long assumed that every collision between two objects in the disk resulted in a perfect merger of those objects,” notes Pilat-Lohinger. “The fact that a good many other things can happen during a collision was simply not taken into account. But with our algorithm and the computing power available today, we can simulate this process much more accurately.”

Start and end of the simulation

Collisions in a binary star system

Researchers estimate that about half of all binary star systems could host Earth-like planets in stable orbits. Pilat-Lohinger and Zimmermann intend to find out how these exoplanets develop. In a 2025 study, they simulated a disk containing 2,000 planetesimals and 25 protoplanets in a binary star system. For this simulation, the researchers used supercomputers from Austrian Scientific Computing.

In their simulation, the protoplanetary disk orbits one of the two stars in the binary star system, while the other star orbits farther away. The gravity of the more distant star influences the orbits of the many objects in the protoplanetary disk and thus planet formation. The closer the second star, the greater its influence.

Earth-like planets

With the help of their simulation, Pilat-Lohinger and Zimmermann aim to clarify whether these disruptions lead to the formation of more or fewer Earth-like planets, how these planets arrange themselves in their orbits, and whether the planetary orbits are stable in the long term. Pilat-Lohinger explains, “What makes this work so special is that we can not only simulate many more objects but also model their collisions in a more complex way.”

For this purpose, Pilat-Lohinger and Zimmermann use a classification system for collisions based on how fast and at what angle the objects collide, and on their masses. These data are provided by their simulation. Collisions can represent not only a perfect merger of the objects but can also include glancing blows or a catastrophic impact in which the objects are destroyed.

This initial study in the context of the FWF project provides the researchers with new insights into the formation of exoplanets in binary star systems. The simulation illustrates, for instance, that collisions tend to accumulate material when the protoplanetary disk and the second star move in the same plane – just as in the solar system, where all the planets orbit the Sun in roughly the same plane. However, if the second star’s orbit is inclined relative to the disk, there are more destructive collisions.

“Our results show how sensitive planetary formation is to such gravitational influences,” says Pilat-Lohinger. “Our project is a small but important step in the search for Earth-like – and perhaps even habitable – exoplanets in star systems where two ‘suns’ can be seen on the horizon in close proximity, allowing one to observe a double sunset.”

About the researcher

Elke Pilat-Lohinger is a senior scientist at the Institute of Astrophysics at the University of Vienna, where she also acquired her Ph.D. She then conducted research in Nice with an Erwin Schrödinger Fellowship from the Austrian Science Fund FWF. Since 2000, she has been working again at the University of Vienna on FWF-supported research projects. Her research ranges from exoplanets and their formation to the stability of orbits and astrobiology. In the summer of 2026, Pilat-Lohinger was honored for her research on small objects in the solar system with an asteroid named after her. The FWF project “Terrestrial planet architectures in HZs of stellar systems” is set to run until 2028.