JWST finds hydrocarbons likely to form Earth-like planets

Orbiting a young star, the molecules could give us insight into how Earth formed...
07 June 2024

Interview with 

Inga Kamp, University of Groningen

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The James Webb Space Telescope has observed hydrocarbons in a disk surrounding a young star. To find out why it matters, Will Tingle has been speaking with Inga Kamp at the University of Groningen…

Inga - In our observing programme we focused on a number of well-known discs around stars that have masses like the sun, but also what we call very low mass stars, so masses of about a 10th of the solar mass. Our goal was to actually characterise what the discs' chemical composition looked like in the inner few astronomical units where we know that rocky planets could be forming right now.

Will - The idea is then that if you can tease apart the chemical composition of this area that's closer to the sun, you might be able to work out how rocky planets such as Earth may have formed.

Inga - Yes. That is the basic idea. It's very hard to observe the planets themselves. I mean, first of all, they are still in the stage of forming when we look at these objects because the discs we study are typically a few million years old, maybe a million years old. A rocky planet typically forms over much longer timescales, so at the moment we are observing these discs, maybe such a rocky planet has assembled about half of its mass at most. We are actually studying these environments at a moment where the planets are actively assembling.

Will - And this particular disc that you found that's orbiting a young and very low mass star has revealed abundant hydrocarbons. Is this particularly rare? Because when we talk about carbons out in the universe, people do get pretty excited because, well, our life is carbon based.

Inga - Yes. That's true. However, when we look at space, and certainly when we look at the clouds of gas and dust from which young stars are forming, usually we see more oxygen than carbon. So what we most often see is water, carbon dioxide, OH. This is also what we typically see when we look at young discs around solar type stars. But what we see in this particular study is very different. So this is a disc around a very low mass star, 1/10th of the solar mass, and here we see abundant hydrocarbons. This is very unusual. The Spitzer Space Telescope had actually seen one particular strong emission feature which was due to acetylene, but we did not expect to see so many hydrocarbons in this disc. So that was really, completely unexpected, and I have to say that the infrared spectroscopy itself is very difficult to carry out. There are instrument artefacts, for example, that need to be corrected. When we saw this spectrum and we were convinced after some time that all this ringing, all this up and down that we see in the spectrum is actually due to molecular emission due to small hydrocarbons, this really blew us totally away.

Will - Do we know then, if this is such a rare occurrence, how those hydrocarbons got there?

Inga - Well, that is something we are still trying to understand. I think the most interesting thing is that with the James Webb Space Telescope, we can really look so deep into these discs that we see all these abundant hydrocarbons. Because if you see only one molecule, it's very hard to piece together: why is it so abundant? Why is it so dominant? Why don't we see water? But if we now see all these hydrocarbons, we have a new view into these inner disc chemical factories, and we can hope to decipher how did these hydrocarbons originate there. We can piece together the chemical pathways that led to their formation in the warm inner regions, and I think that is the power of the new James Webb Space Telescope compared to what we had earlier, that we can really see these minor species as well. We need all of these species in order to get the full, complete picture of how these discs evolved into what we see right now, namely, this very carbon rich gas signature.

Will - Since these discs then eventually go on to end up forming planets, do we anticipate anything different happening to a planet that is formed with these hydrocarbons?

Inga - Well, that's an interesting question. First of all, there are different types of planets that could be forming in these discs. There are rocky planets, and then they're predominantly made out of solids, but there are also maybe gas rich planets, maybe around the size of Neptune or a little bit smaller. Of course, if that gas that we see now in the molecular emission in the infrared, if that ends up being part of a gas planet, it will make a very interesting gas planet because we don't know of any of these in our own solar system. We do have Titan which has a very carbon rich atmosphere as well. But in terms of the normal planets, Jupiter, Neptune, and Saturn, they do not look like this.

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