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About an up-and-coming Squamish astronomer

Quest University graduate's research shining bright
ESA C. Carreau
Artistic rendering.

Recent Quest University graduate Arnaud Michel has his eyes trained on the stars, literally.

His research looks at planet and star composition and formation.

His findings were published last summer in the peer-reviewed academic journal Astronomy & Astrophysics.

The Chief caught up with Michel over Zoom from Kingston, Ont., where he is currently pursuing his master's degree at Queen's University.

What follows is an edited version of that conversation.

Arnaud Michel
Arnaud Michel. - Courtesy Arnaud Michel


Q: You graduated from Quest in 2020. Where did you grow up?

A: I grew up all over. My parents work in hospitality, so we travelled a lot. We lived in tropical places, mainly.

I am originally Swiss, but we grew up abroad. We went to international schools. Before Quest, I went to United World College Maastricht (UWCM), in the Netherlands.

The idea of UWCM is to bring students together from all over, from different socio-economic and cultural backgrounds. Some upper-year students there told me about Quest. I began there in 2016.

Q: You have lived so many places, what did you make of Squamish?

A: For me, it was really great. Having never lived in a big city, Squamish was just the right size. There was plenty to do and lots of restaurants and it is accessible, to a great extent — I had a bike and friends had cars. It wasn't overwhelming and it was welcoming. I hike a lot and I started skiing while at Quest.

Q: Can you explain in simple terms what you studied at Quest in terms of astronomy?

A: At Quest, we have questions that we delve into during our time there. My question was: "How do planets form?" We know there are other planets in our system and since 1995, we have started to discover exoplanets — planets that orbit stars that aren't the sun. Suddenly, there has been this wealth of information that there are planets everywhere. So how do they come about?

Stars and planets must form and at the end of the day, these are two very inter-related processes. The star forms and right around it, initially there is a disk — like a CD essentially — with the star in the centre and the CD is a protoplanetary disk. That is a disk of dust and gas.

These disks of dust and gas in which a planet forms, share a very similar composition to the star that it is around. So, it has been suggested that the composition of a star is related to the composition of rocky planets, such as Earth. Thus, there is a good link between Earth's composition and Mars's composition and our sun's composition.

Previous studies have looked at different parts of our galaxy. Around the Earth we have a thin disk, which forms a thin layer and above that there is a thick disk and it is all englobed in the halo — a big round sphere. That is our galaxy.

It turns out the stars in these different parts have a different composition because of their age. Our sun is located in the thin disk, which is the youngest. And then as you go to the thick disk, it is older and then the halo is the oldest. And because of this age difference, there is a compositional difference in the stars. The research that I conducted, looked at how the planet sizes vary between stars in the different parts of the galaxy — in the thin disk, in the thick dist and the halo.

This was done through modelling. We predicted what size the planets should be.

Q: To be very basic about it, is that like when you look at the rings of a cut tree trunk and they are different sizes because of the era when they were formed?

A: Exactly. At a different point in time, there's a different composition in the galaxy so the stars that form at that point in time have more metals — iron — for example. The younger stars have more iron than the older stars.

When you have more iron, the planets that form will be denser.

Q: Why does this matter?

A: What we found is that the differences are statistically small. We predicted a couple of percentage points difference overall.

That was interesting in that you don't suddenly have a planet that is the same mass as the Earth, but four times as big, leading to the idea that we could have a very old planet with very similar conditions, although its composition would be slightly different.

You don't suddenly have 10 times as much gravity or no gravity at all. The conditions are going to be quite similar.

Recently, there have been discoveries of bigger planets that were observed.

Our modelling looked at statistical differences so some will be bigger, some smaller.

This is exciting. We are starting to observe these old rocky planets and we now know they exist. It is not just, "we think they might be there and we think they might be a tiny bit bigger." There's proof they do exist.

Q: From your voice, it is obvious you are passionate about this work. What do you think draws you to it?

A: I think because we lived on tropical islands as I was growing up, the night skies were very clear.

Then when I was studying in the Netherlands, it was my physics teacher, Dr. Virpi Mähönen, who introduced an astronomy module and something clicked and I found it really interesting and exciting.

My wonder was developed.

Q: What is next that you are studying with your master's degree?

A: I am working with Professor Sarah Sadavoy at Queen's. We are trying to study the geometries of the young disks. When a star forms and immediately after, very early on, what do these disks look like? This is based on observations that have been done at an observatory in Chile, called the Atacama Large Millimeter/submillimeter Array (ALMA). The data has been taken so now it is a matter of trying to look at the data for a dozen or so young stars with disks. This will tell us more about these initial stages of planet formation.