SRON researcher Dr Remco de Kok will use a Veni grant from NWO to investigate the atmospheres of exoplanets. De Kok has received 250,000 euro to develop a more accurate algorithm for determining the composition of planetary atmospheres.

The first exoplanet (planet outside our solar system) was discovered in 1995 and now almost 500 such exoplanets are known. Studying these, often exotic, exoplanets and comparing their characteristics with those of the planets in our own solar system will give us a better understanding of how planets are formed and evolve. Unfortunately, we still know very little about the vast majority of exoplanets discovered to date, simply because even with the biggest telescope they are too far away to observe. However, researchers can now deduce the composition of exoplanetary atmospheres using the so-called ‘transit’ measurement method.

Transit method

This method is suitable for exoplanets that move in front of their star during their annual orbit. During such a ‘transit’, the starlight reaching the telescope also contains light that has travelled through the planet’s upper atmosphere. It therefore contains traces of the chemical composition of those layers, such as gasses that absorb starlight at certain wavelengths. For example, water vapour and methane gas have been discovered in exoplanetary atmospheres using the transit method.

Thanks to the Veni grant from NWO, Remco de Kok can spend the next three years improving the analysis of transit measurements. De Kok will do that research within the Earth & Planetary Science (EPS) division of SRON Netherlands Institute for Space Research. The researchers there have considerable experience with algorithms for the analysis of earth observations in particular, but of other planets as well.

Scattering
De Kok: ‘The current algorithm assumes that starlight can only be absorbed during its journey through the planet’s atmosphere. Yet research on the earth and other planets in our solar system has now revealed that starlight is also scattered by molecules, aerosols (small particles) and cloud particles in the atmosphere. That scattering can strongly influence the strength of signals from atmospheric gases, such as water vapour and methane, with the result that researchers can misestimate the quantities of such gases present. Furthermore, the transit measurements contain information about the scattered particles which we cannot extract at present.’

De Kok will first of all test the new algorithm using measurements from atmospheres of planets in our solar system and only then will he use it on measurements from exoplanets in transit. Eventually, it will also be possible to use the method to improve the design of new generations of measuring instruments. De Kok: ‘Then in the future we will be able to make even more accurate transit measurements still. That would give the search for earth-like planets outside our solar system an enormous boost.’