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Astronomy: the three tiers of research


An illustration of 51 Pegasi, the first planet to be discovered orbiting a sunlike star.

We have no reason to think that the planets in our solar system represent every type of planet in existence, according to the Swiss astrophysicist Michel Mayor, who discovered the first extrasolar planet with Didier Queloz in 1995. Last April, his team at the Geneva Observatory discovered the smallest exoplanet known today.

Interview by Marie-Christine Pinault-Desmoulins


The great scientific discoveries are often the result of chance. Was this the case for the first planet discovered outside of our solar system?

No, it wasn’t a stroke of luck if that’s what you mean. It was the outcome of a long process of research and the development of instruments to accurately measure the speed of stars. The spectrograph called ELODIE at the Provence Observatory [France] allowed us to detect the first exoplanet and was designed precisely in order to look for planets outside of out solar system. Where we were lucky was in discovering some planets that revolved around their orbit very quickly. The orbital period of 51 Pegasi b is only 4.2 days. To give you an idea, by contrast the orbital period of Jupiter is 4332.71 days - approximately 10 years. It is without doubt that objects with a shorter orbital period are easier to discover and observe. In a few nights you can make observations that in other cases would take you 10 or 20 years.

What is your most important current research?

In the short run, I would say that the research follows three main themes: comparative planetology, the detection of lighter planets and planetary imaging. The first field combines data from satellites and ground instruments to determine the average density of planets. These studies aim to know the physics of planets. This is very important since we have no reason to believe that the planets in our solar system represent every type of planet. In theoretical terms we can predict that, for example, there are planets made of melted ice. This would be the case with Neptune. If it approached the sun its surface would be covered with oceans. But this sort of ocean would have nothing to do with the type of ocean we have here on earth because it wouldn’t have a rocky bottom Regarding the search for lighter planets, you must know that until recently we’ve been able to detect extra solar planets that are as small as four times the mass of Earth. That’s already almost 100 times lighter than Jupiter! In our jargon, we call them “Super-Earths”. But thanks to new instruments we have discovered a telluric exoplanet only two times the mass of earth. [Note, the Geneva Observatory announced the discovery of Gliese 581 E on the 21 April.] These discoveries are made by indirect measures. At the same time, planetary imaging that allows us to see the exoplanets directly is taking off. At the end of last year, we had great success in obtaining images of some very large young planets. But please note this doesn’t mean we will now be flooded with images, because the vast majority of exoplanets cannot be seen easily: either they are already cold, or they are too close to their stars. Currently, the Geneva Observatory is in the process of developing, in collaboration with partners, a tool called SPHERE for direct imaging of exoplanets, which will allow us to see these tiny planets. It should be operational in 2011. More than 200 people have been working on it for over 5 years.

Is there much international collaboration in the field of astrophysics?

Currently the most common collaboration is person to person. There isn’t any real international collaboration. It must be said that in certain areas it isn’t necessary or even desirable: competition is positive. However, the search for life in the universe necessitates international collaboration. This field requires considerable resources and it is probable that the existing organizations aren’t adequate for promoting this type of mission effectively. This ambitious mission has largely been put on hold for budgetary reasons, both from ESA (European Space Agency) and NASA (National Aeronautic and Space Administration of the United States). Some researchers dream of a type of institution which could coordinate these studies on a global scale, but for the moment this is wishful thinking.