Paris, 18 June 2002
An interview with Didier Queloz, one of the world's most successful planet hunters.
The last five days have witnessed the unprecedented announcement of 25 new planet discoveries. These discoveries are split almost evenly between European and American astronomers. Didier Queloz and his colleagues at the Observatoire de Genève, Switzerland, have found a dozen of the new planets. Their discoveries include the most tantalising one yet: a planet that closely resembles Jupiter in our own Solar System. The find brings astronomers another step closer to detecting an Earth-like world.
Queloz is a member of ESA's Scientific Advisory Group for its Darwin planet-search mission. On Friday 14 June 2002, Queloz previewed his latest work at ESA's European Space Research and Technology Centre (ESTEC) in the Netherlands.
Which new discoveries have you made?
We have found 12 new planets. Among them, a new multiple system and most excitingly, a planet very similar to Jupiter (the biggest planet in our Solar System) in the sense that it is about the mass of Jupiter and has a similar orbit. Such planets are called Jupiter analogues by planet hunters and have long been a goal of such searches. It takes 7 years to orbit its star whereas Jupiter takes 12 years (known as the orbital period). The radius of its orbit is about 3.7 AU and Jupiter's is 5.2 AU. (1 AU is the distance between the Earth and the Sun.and is about 150 million kilometres.) The key element, however, is that it has a circular orbit, not an elliptical one. This reminds us strongly of our own Solar System.
The American-led team announced a much larger planet in an elliptical orbit at about the same distance from another star as Jupiter is from our own Sun. Together with your own Jupiter analogue, do these discoveries mean that planet hunting has entered a new phase?
Yes, we are getting much closer to seeing solar systems like our own. The first planets we detected were the ones with short periods, completing an orbit in just a few days. They were the easiest to detect because they give the largest signals. Long-period planets take many years to complete a single orbit and you have to track them for a whole orbit. We have been following this one from the beginning (nearly a decade). They also require better sensitivity. This new planet makes its star move by just 17 metres every second compared to 59 metres per second for the first planet we detected in 1995. Now that we can see long-period planets, we can check for multiple planets in systems already known to contain a single planet and also look for Jupiter analogues that may indicate solar systems like our own. In this way, we can build up a more complete picture of the variety of planetary systems.
What does the future hold for European planet searches from the ground?
The future is great. We are building a new instrument for European astronomers with the European Southern Observatory (ESO). This instrument is called HARPS and will be installed on the 3.6 metre telescope in La Silla in Chile. Compared to what we are doing today, HARPS will be about 100 times more efficient, allowing us to reach sensitivities of about 20-30 centimetres per second. We are planning to test it in the laboratory in one month's time and we have commissioning time scheduled on the telescope in February next year.
How important are ESA's space-based planet search missions?
They are essential. To me, the Eddington mission is really the next step because it is the only way to reach Earth-like systems. Eddington will use the transit method and detect the drop in a star's light, caused by a planet orbiting in front of it and if you want to get enough accuracy to detect the transit of an Earth- sized world you need to go into space. Eddington will detect ten or a hundred times more planets than we can from the ground. Then Gaia will open another window because it should detect something like ten thousand planets. This is a crucial next step after Eddington because if you look at the past history of stellar astrophysics, people start to understand what is going on only when they can study a few thousand examples of celestial objects.
Finally, the Darwin mission will attempt to take pictures of Earth-like worlds and analyse their atmospheres for signs of life. What do you consider are its chances of success?
ESA's Darwin is a fantastic project for me because, behind all of this planet quest, is this question of life on other worlds. I am optimistic. Why should Earth be a kind of strange system with life? If we try to look for other intelligence, however, then I think they might be rare; perhaps there is only one civilisation per galaxy. But for basic life, I'm sure it has to be there. So, Darwin is very likely to be successful.
About ESA's planet-search missions
ESA's planet-search missions, Eddington, Gaia and Darwin are part of the Cosmic Vision 2020 science programme.
Eddington is scheduled to launch in 2008 and, as well as planet searches, will be capable of detecting the equivalent of earthquakes on nearby stars, giving astronomers key data about their interiors.
Gaia will be launched no later than 2012 and will survey the nearest one billion stars to provide the most precise positional and brightness data ever. This will be invaluable to every aspect of astronomy, from nearby asteroid searches in our Solar System to cosmology and the fate of the Universe. Gaia will detect planets by the transit method and by the way stars wobble in response to their planets' gravitational pulls.
Finally, Darwin is in the planning phase, with new technology being vigorously developed. It will launch around the middle of the next decade and consist of a flotilla of eight spacecraft that will fly in formation and combine their observations to detect the light from Earth-like planets around other stars. By analysing that light, astronomers will be able to deduce the chemical compositions of distant planets' atmospheres and search for the telltale chemicals related to life.