Comets: valued primitives of our solar system

DW: Most people like to observe shooting stars, such as from the Perseid meteor shower, just because it looks nice. But what sort of scientific research is being done in the area of meteoroids, comets and asteroids?

Professor Thierry Courvoisier: Indeed, when you watch these meteors at night - the shooting stars - you're watching something interesting, it's very nice, and it gives us information about the path of the comet, from which this material stems, as it orbits the sun. But there's not much more you can do with these observations.

You can do more when you find bits and pieces of the meteoroids, the bigger pieces, that have hit the Earth [meteorites]. Then it starts to get interesting. And it's almost the same as when you research comets. You're after material which is very primitive in the solar system. When you look at the Earth, you have material which was put together at the time the solar system was formed. But all this material has been processed and reworked - you have the oxygen and the carbon, which came to the surface, and the iron which went down - so you have material which has been changed by geological phenomena and by life after that. But when you look at these meteorites from comets, you have pieces of material which have undergone very little change, and hence you can find out what materials existed in their composition at the very early stages of the formation of the solar system.

So when we say "primitive" we're not talking about age, we're talking about the fact that these objects are unadulterated…

Exactly. And, in any case, the age is a different thing, because this matter - anything which is not hydrogen and helium - was processed in stars before the formation of the solar system. So it's not the age of the atoms, per se, which is relevant, but it's the way in which the matter was put together in the process of the formation of the solar system. That's what is at stake in this research.

Do you think there is any relevance in all the talk about the numbers of meteors we see - are the numbers significant when we can't yet determine the absolute numbers?

Yes, the numbers are significant but for a completely different reason. The question there is the probability that an important piece of material falls on the Earth and causes significant damage. So in order to know that you have to know the "distribution," the number of pieces of material that are swirling around in the solar system as a function of the size of these pieces of material. And it starts to get difficult with the smaller pieces, because it is difficult to observe them. But the smaller pieces can still be large enough to cause very significant damage on the Earth. And so that sort of study is important.

We do a lot of observation of these events from Earth. Do you think we should do more observation from space-based satellites or spacecraft - would that improve our understanding?

Yes, indeed. That's what is being done with Rosetta [the European Space Agency mission]. If we go back to the start of our conversation, we talked about the origin of the solar system and the material that is there... it's absolutely crucial to go on these comets, the larger meteoroids, and the larger pieces between Jupiter and Mars to see what they are made of. And one example is Rosetta, which measures the composition of water. Water is always hydrogen and oxygen, but there are different types of hydrogen. And the question is, where does the water we have on Earth come from? What made this water? Many people thought Earth's water came from comets, when lots of comets arrived on the Earth. But observations made by Rosetta show the types of water on comet 67P/Churyumov-Gerasimenko, which it is investigating, is not the same as the water on Earth. So what that shows is these kinds of comets are not the origin of the water that you and I drink. That's a very nice illustration of the type of research that can be done in space, but which you cannot do anywhere else.

Professor Thierry Courvoisier is an astrophysicist and outgoing president of the European Astronomical Society. From 2017 to 2019 Courvoisier holds the presidency of the European Academies Science Advisory Council. He has authored or co-authors two books and more than 400 scientific publications. He has held positions with the European Space Agency and is a professor of astronomy at the University of Geneva.