But this also presents a difficulty. These stars only emit a small amount of light, most of the time they can only be detected in the infrared by the most powerful instruments. Those that are closest to the Earth have just begun to be studied and TRAPPIST-1 has itself only recently been discovered. At distances of around one hundred light years they remain unobservable while more massive stars like the sun emit a signal that is visible over distances of several thousand light years. “Therefore, there are a lot fewer known ultracool red dwarf stars than large stars due to the fact that we can only detect the closest ones. Up to now, research campaigns have concentrated on finding as many exoplanets as possible while probing large sections of the heavens without categorizing the type of stars. This made it possible to study thousands of stars at the same time therefore increasing the chances of detection, but included almost no ultracool red dwarf stars”, explains Emmanuël Jehin. Finally, up to the present time, the scientific community has depicted these stars as being too active, with an emission of light that is too variable to allow for the detection of planetary transits, the presence of which was very doubtful anyway, according to the results of several models. In a nutshell, these planets were considered to be of little interest for planetary research due to the fact that they were so different from the sun.

The researchers from Liege think the opposite and they believe that almost all of these stars hide a planetary system as this first discovery seems to confirm. Concentrating on ultracool red dwarf stars would seem to be a promising prospect. “In addition”, adds Michaël Gillon, “the large telescopes of the future such as the JWST, NASA’s next space telescope, will have a degree of precision that will enable them to study the atmosphere of Earth-like planets and even find traces of life, but only around the nearest and smallest stars. For bigger stars that are further away, we will have to wait for more powerful instruments”.

An exceptional start to a project

For the SPECULOOS project, the challenge will therefore be to observe all the ultracool red dwarfs near the Earth. “In total, we have detected around a thousand stars that are sufficiently nearby to enable us to conduct subsequent studies of the atmosphere of Earth-like planets transiting them”, says Michaël Gillon. “They are distributed just about everywhere in the sky and we have almost no chance of finding two of them in the same field. While NASA’s Kepler space telescope can probe thousands of stars at the same time, we have to study them one by one by observing each of them in turn for around ten nights on average.  It is a very slow process which obliges us to use several telescopes in order to finish the project within a reasonable time frame”. Another practical difficulty is the fact that, in order to detect a transit, a planet must pass exactly in front of its star as seen from the Earth, which is a statistically rare occurrence. “Given this fact, interjects Emmanuël Jehin, “relatively large telescopes are very sought after in order to be able to focus on one star in particular for a period of several nights. Unless of course it is a star around which we have already discovered planets which are worth studying. Having our own telescopes was therefore vital for the project. We can devote the necessary time to this research. It is a challenge and a risk we are willing to take”.  

Before fully launching the SPECULOOS project, it was necessary to ensure the viability of such a wild intuition and launch a prototypical version. “The project is ambitious”, acknowledges Michaël Gillon who is the head and creator of the project, “and given the reputation of these stars, we needed to be sure that we have a chance of detecting Earth-like planets. We knew that TRAPPIST was too small to meet the demands of such a large sample. However, it could easily observe the brightest ones and the ones that are nearest to each other. We therefore selected fifty target stars which was enough to be able to draw statistical conclusions before going any further”.