Yann Alibert and Matthew Hooton are eagerly awaiting the planned launch of the James Webb Space Telescope (JWST) on December 22, 2021. In this interview, the two astrophysicists from the University of Bern tell how they managed to get observation time with JWST and what this has to do with CHEOPS.

Could you explain in simple terms what your research is about?

Yann Alibert: I am studying how planets and planetary systems form and evolve. I am mainly a theorist and do computational work in order to make predictions about the interior of the planets and what they are composed of.

Matthew Hooton: I am observing exoplanets and more specifically the transits of exoplanets. When a planet happens to have an orbit that passes between its stars and us watching it, an amount of the light of the star is blocked by the transiting planet. And by measuring this amount, we can tell quite a few things about the planet and the star. It also gives us clues about what the atmosphere of an exoplanet is made of.

Why are the atmospheres of exoplanets so interesting?

Yann Alibert: Well, there is obviously no question of travelling to exoplanets. Everything we know about exoplanets we know from their atmospheres. If we want to understand these planets, how they formed and evolved, we have to understand their atmospheres.

Matthew Hooton: As pointed out before, we use the transits to learn something about the atmosphere of an exoplanet. A fraction of the light of the star is filtered through the atmosphere of the planet when it passes in front of the star. If this filtered light is analyzed, conclusions can be drawn about the chemical composition of the atmosphere of the planet because different atoms and molecules in the atmospheres leave behind recognizable “fingerprints” in the light. We can work out all the different abundances of various molecules, such as water, carbon monoxide, or carbon dioxide for example. By using sophisticated atmospheric models we compare the abundances of molecules in the atmospheres of the planets in a system to each other and this gives us information about where in the formation disk of the system the planets formed.

You were involved in the paper about a unique planetary system that was detected with CHEOPS.

Matthew Hooton: Three transiting planets in the system were originally identified by the TESS satellite. We then got eleven days of continuous CHEOPS observation because it was such an exciting system. This allowed us to correctly identify the orbital periods of the known planets and discover three previously unknown planets, bringing the total number of known planets in the TOI-178 system to six. The orbital periods that they have are in a very specific pattern that causes the planets to exert uncommonly strong gravitational forces on each other.

Yann Alibert:This is quite rare, and in terms of formation of the planets it would take a very specific history to get to that point. And the other reason the system is so interesting is that there is an irregular pattern of the densities of the planets. Usually, the further away a planet is from the star, the lower its density. This is not the case for TOI-178. So, once you put these two things together, it is really hard to explain how this system formed.

Now you have obtained time with JWST to observe that extraordinary system further.

Yann Alibert: As pointed out before, we already know a lot about the system. The observations with JWST will bring on top of that information about the composition of three of the planets of the TOI-178-system.

Matthew Hooton: We will be observing one transit of three of the planets in the system. And each observation will last about six or seven hours. That will give us information of the atmospheres of three planets which are located at different points in the system.

You must be absolutely thrilled to be able to work with JWST.

Matthew Hooton: We didn’t have very high expectations because a lot of people were applying for observation time and obviously, they had very good science cases to propose as well. I have worked quite a few proposals for telescopes in the past. But JWST is just on a different level – also in making sure that everything is correct. We were thinking about science questions that we could answer with JWST. Not only did we have this really interesting system where there is some strange physics going on as it were, but the system was really favorable for observation. So, we had to go through a detailed check of the technical aspects of the observations and the exact sort of strategy we wanted to propose. We were then bringing in people from across the CHEOPS team who have the relevant expertise to define what was realistic. At the earliest we think the data could be taken hopefully by this time next year, that is in the second half of 2022.

So, one could say that you were able to obtain observation time with JWST is thanks to CHEOPS?

Yann Alibert: A key thing with JWST is to exactly know beforehand what to observe and when. Thanks to CHEOPS, we exactly know the orbits of the planets in the TOI-178 system and when their transits will occur. It is indeed a good demonstration of why CHEOPS is so important. Its flexibility and high precision allowed us to confirm TOI-178 as an interesting system to be observed with JWST. With JWST you don’t even want to waste one hour waiting for a planet to transit. Time is very precious when it comes to something that cost billions to put up in space.

Working with the JWST seems like a dream come true. Yann once told me, he that he dreamt of becoming an astronaut as a kid as a lot of astrophysicists did. How about you, Matthew?

Matthew Hooton: It is a bit embarrassing, but to be honest, I must have done it at some point as well. But the skills required to become an astronaut would be to be a very good soldier or very good at flying planes for instance. I guess I realized slightly later on that astronauts mainly have to follow a very strict set of orders. Which is on a certain level less interesting than what we do. We can work out the interesting questions that we want to answer. And I think that is one of the most appealing aspects of a job in research is that we can decide what we think is interesting and spend our time following that and trying to find answers. Although, I must admit, going to space looks fun.