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What tiny isotopes reveal about planets outside our solar system

Planets existing in other solar systems contain invaluable information about the origin of planets and life. PhD candidate Yapeng Zhang has studied their atmospheres by looking at their smallest parts: isotopes. With her research she hopes to discover what makes our own solar system unique.

Looking at how things are elsewhere is a good way to learn more about oneself. That approach applies to space as well. Although our solar system feels immense, it is just a tiny dot in the vast universe. Therefore, looking at our neighbors can help putting things in perspective.

Yapeng Zhang, originally from China and finalising a PhD at the Leiden Observatory, looked at so called exoplanets. ‘The eight planets in our own solar system merely show a glimpse of the universe's possibilities,’ she says. ‘There are millions and millions of planets that orbit around other stars, or sometimes around no star at all.’ Zhang wanted to know more about these far away planets: where and how they are formed, and what they reveal about our own solar system.

The VLT, a huge telescope in Chile, provides the data

One way of understanding these exoplanets is by examining their isotopes. Isotopes are atoms that vary in how many neutrons they have in their nucleus. It might feel counterintuitive to look at the smallest of particles when studying planets lightyears away. However, isotopes contain a lot of information about when and how a planet is formed.

Zhang relied on data provided by the Very Large Telescope (VLT). This huge telescope in Chile was the first one to make an image of an exoplanet. Trough the telescope, it is possible to distinguish atoms or molecules in the atmosphere of an exoplanet by monitoring how they absorb light. Every species and isotope has its own way. ‘We first remove the noise,’ Zhang says, ‘and then extract the signal of the specific isotopes we are looking for.’

Same technique can be applied to dinosaur bones

Interestingly, the same technique has been used to look into the history of dinosaur bones. ‘And in our own solar system, the isotopes of hydrogen we find on the planets Saturn and Neptune are quite different,’ Zhang says

‘This really is a new field. The first exoplanet was found only in 1995.’

She focused on a super-Jupiter, a huge planet many times the mass of ‘our own’ Jupiter and five times as far away from its sun. She also looked at a brown dwarf, or a ‘failed’ star. Being two very different objects, it allowed Zhang to attribute isotope ratios to each of them, creating a framework for further research. For example, in the atmosphere of the super-Jupiter she found a larger than expected ratio of the isotope carbon-13. That might sound abstract to outsiders, but scientists like Zhang know this could mean the planet was formed at a great distance from its parent star. 

First exoplanet was discovered only in 1995

Zhang’s research is just a first step, but the ‘isotope approach’ offers a promising new window on planets in other solar systems. ‘This really is a new field,’ Zhang says. The first exoplanet was found only in 1995. ‘And since, we have detected more than 5.000 of them, with the number growing rapidly. The PhD candidate, who will continue with a postdoc, is eager to dive into new data that came from the VLT and will be analysed in Leiden. ‘We are working on a large programme with several PhD students involved. This is really exciting.’

Text: Samuel Hanegreefs

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