Leiden methods speed up search for extraterrestrial life
Astronomer Ignas Snellen investigates the atmospheres of exoplanets, with the final goal of finding signs of life. This is becoming easier thanks to the ever more effective measuring methods of his research group. ‘Within ten years it’s going to get really exciting.’ Inaugural lecture on 8 November.
There is a multitude of planets that might be similar to the Earth. This was announced by American astronomers earlier this week, when they speculated, on the basis of a study of ten thousand stars, that the Earth might have as many as 10 billion twin sisters. ‘It is all developing so fast!’ emphasises Ignas Snellen. Twenty years ago we only knew our own solar system with its 8 planets. In 1995 scientists discovered the first exoplanet, i.e. a planet orbiting around another star than our sun. As for the 10 billion referred to by the Americans, they are so far only theoretical. Every month, proud groups of researchers announce their discovery of a new planet. ‘There is an intense planet race going on. We are participating in the atmosphere race.’
We are quick to call them sisters, these newly discovered planets of a size similar to that of the Earth and with an estimated temperature – not too hot and not too cold – that would allow for liquid water, but this is all speculation. Are these sisters also rocky planets, or will they turn out to be gas balls, or chunks of ice? They are too far for us to send a robot. But we will in future be able to investigate the composition of the atmosphere of these planets. To do so, we need very sophisticated measuring methods, and that is what Snellen and his research group specialise in.
The Leiden astronomers hope to be able to check for signs of life, such as oxygen, ozone or methane gas in approximately ten years time. Until recently, astronomers thought that it was only possible to do this using space telescopes, because ground-base observations were distorted by our own atmosphere. Snellen: ‘We developed a technique to filter out this effect. Five years ago we were the first to observe an exoplanet with a ground-base telescope. Now this technique is used by everyone. A space telescope is approximately 1.5 metres in diameter, costs one billion Euros and is incredibly fragile. With that money you can build a ground-based telescope with a diameter of 40 metres which can observe more.’
The discovered exoplanets usually turn out to be gas giants, i.e. giant planets that consist primarily of gas and that are easier to investigate due to their large size. ‘They form a good practice field to test our techniques. Terrestrial planets are still too small and too far for us to accurately measure their atmosphere with our current techniques.’ His group discovered carbon monoxide in the atmosphere of 5 gas giants, and water vapour in two more.
Snellen and his colleagues are using the largest ground-base telescopes available, which are located in Chile and on the island of La Palma. Within ten years they hope to start using a new telescope: the planned European Extremely Large Telescope in Chile. This telescope will have a diameter of 40 metres and be at least 25 times more powerful. ‘That will be really exciting, because it means we will be able to investigate the smaller, terrestrial planets.’
In the meantime, the Leiden astronomers are refining their techniques for light and colour measurements. Until now, astronomers were able to make measurements up to one hundredth of a percent. Together with other Leiden research groups, Snellen is developing a method to more precisely observe the colour of gasses, which makes it even easier to determine their composition. ‘With this instrument, called METIS, we can probably measure signals of one millionth of a percent and that will bring the terrestrial planets within reach of our investigation.’
And now the burning question: what are the odds of finding extraterrestrial life? Snellen: ‘In ten years time we will be able to make much more precise measurements and we will be able to start searching for the first signs of life. It will most probably be very simple bacterial life. The odds that we will find intelligent life in my lifetime are very small. Bacterial life can originate quite quickly once a planet cools down. Intelligent life develops much more slowly and therefore has to be much rarer, so it can only be found at much greater distances. The modern human only appeared after 99.99 % of the current age of the Earth. But of course, these are speculations.’
(7 November 2013)
Fundamentals of Science is one of the key themes in the research of Leiden University.