The missing Tatooines out there

28 June 2021

If you are a Star Wars fan, you surely remember the amazing view of double sunrises and sunsets in Tatooine, Luke Skywalker’s home planet. In real life, Earth-sized planets may be much more common than we think — and like Tatooine, a lot of them might be among two stars, or binary systems. 

Astronomers recently found that we are missing a lot of these distant worlds. As at least half of all stars in the Universe are combined in binary systems, they could be ‘hiding’ plenty of planets we’re not aware of. 

There’s a good reason for it: planets in binary systems are quite difficult to spot. One of the planet-finding techniques astronomers most commonly use is called ‘transit’: it measures the ‘shadow’ a planet makes when it passes in front of a star. If you have a second star around, the change in brightness in the first star will be a lot harder to see. 

NASA’s TESS mission has found 131 exoplanets so far, with over 4,000 candidates being studied for confirmation. But what if there are even more? With that question in mind, a team of astronomers used the twin telescopes of the Gemini Observatory to look at TESS findings with better resolution. Guess what they found? A lot of stars that look like an only bright light far in outer space are actually binary systems! 

After finding that out, the team compared the sizes of planets that normally surround a single star to those that orbit binary systems. While single stars have planets of different sizes around them, only large planets orbit binary systems. This is why astronomers think there are a lot of Earth-sized planets around binary stars that we just have not been able to spot yet. 

Another interesting finding from this study is that binary stars that are close to one another are less likely to host planets than those that are further apart. Maybe planets do not form around stars too close to their stellar neighbours. 

To confirm the findings, astronomers will need to do some more studies using different techniques. But this is definitely a great step to understand how planets like Tatooine are born and evolve in real life!

Cool Fact

As its name indicates, the Gemini Observatory has two telescopes. Gemini North is located in Mauna Kea, Hawaii, and it is 4,200 meters above sea level — almost half the altitude of Mount Everest! Gemini South is located in Cerro Pachón, in the Chilean Andes, at about 2,700 meters high. Together, both telescopes can look at the entire sky!

Image: The illustration shows a planet partially hidden, bathed in the light of a binary star system.
Credits: International Gemini Observatory/NOIRLab/NSF/AURA/J. da Silva