Leiden planetary experts want to study seven ‘Earths’ in more detail
Astronomers have discovered seven Earth-like planets around a dwarf star in our galaxy. Three of these planets are located in the habitable zone of this star, and may contain liquid water. ‘The next step is to study the atmospheres for signs of life. In Leiden we are experts in that area,‘ says planetary expert Ignas Snellen of Leiden Observatory.
The seven planets are about the same size as Earth. Researchers led by Michaël Gillon of the University of Liege detected them while they passed in front of the cool red dwarf star TRAPPIST-1, only forty light years from here. They used telescopes on Earth and in space, including ESO's Very Large Telescope and NASA's Spitzer Space Telescope.
TRAPPIST-1 is a cold and very small star, about the size of Jupiter. Astronomers suspected that Earth-like planets would orbit such dwarf stars. This makes them very interesting for the search for extraterrestrial life. ‘It is a wonderful discovery - and a big surprise,’ says Snellen. ‘This is the first time astronomers looked at the smallest stars. That they found this planetary system so soon means that our galaxy is full of Earth-like planets. Snellen wrote a Nature News & Views article about the discovery, that was published this week in Nature.
Each of the seven now discovered planets (TRAPPIST-1b, c, d, e, f, g and h) causes a small drop in the brightness of the star when it sure passes in front of it – a phenomenon called planetary transit. By studying planetary transits, astronomers can obtain information on the size, composition and orbits. This led to the discovery that the six inner planets are Earth-like both in size and temperature.
Snellen and his team want to use such transits to study the atmospheres of the planets in order to learn more about their composition and climatic conditions. ‘The discovery of these planets is ideal for our research because we can see the planets from the Earth when they go in front of their Sun. This enables us to study their atmosphere and figure out what gasses they are made out of.’
Signs of life
The three inner planets are probably too hot to have liquid water. The outer planet is just too far. The other three, however, are the holy grail of planet hunting: they are in the habitable zone of their star and might have oceans on their surface.
Snellen: ‘From the Earth, we know that liquid water plays an important role in the evolution of life. But we still have to investigate if there really is life on these planets. If you look from a distance to Earth you can see that oxygen is present in our atmosphere. Oxygen is a waste product of life. The detection of oxygen in the atmosphere of a planet would therefore be a first indication of life.’
James Webb Space Telescope
The new discoveries make the TRAPPIST-1 system an important target of future research. ‘The James Webb Space Telescope – the successor of the Hubble Space Telescope - will be launched next year,’ says Snellen. ‘It will be even more exciting when we can use the European Extremely Large Telescope (E-ELT), of which the construction began recently. With this telescope we could even find traces of life. We hope to get observing time on these objects. Leiden has a good chance, because we are developing special techniques to study the atmosferes.’
Read the Nature publication about the seven planets here.
Header image: ESO/N. Bartmann/spaceengine.org