Liquid water?

Let’s imagine now that these planets cross this ice line but that they do not get too close to the star. The ice is not exposed to temperatures that are so high they would sublimate it or cause an outgassing that would dry up the planets as a result. “At a good distance”, summarize the two researchers, “this ice can melt and form oceans. The two first planets are at the limit of the habitable zone. They are too close to the star. But models have shown that they could harbor habitable regions in the western limb between their day and night sides”. The heat is not distributed in a homogenous way on these planets. The proximity of their star traps them in a state known as synchronous rotation. Like the Moon with the Earth, they always show the same hemispheres, the day side, which is a lot drier than the night side. The prevailing winds, which are too hot to keep water in the liquid state, have a tendency to blow towards the east, preserving a milder region and also brighter than in the west. The third planet seems even more promising and could be totally inhabitable.

A veritable Eldorado

The discovery is as encouraging as it is new. But it is the nature of the system that will be one of the most sought after objects by astrophysicists in the months and years to come. “As the contrast between the size of the star and its planets is particularly favorable and the system is very close, we will be able to study the atmospheric composition of each planet with unparalleled precision”, explains Emmanuël Jehin “We hope to discover  biomarkers like water molecules, carbon dioxide, ozone etc. If these traces are in proportions similar to those of the Earth, it would be even more incredible. We could also imagine that these planets, given their proximity to their star, are subject to significant volcanic activity. That would also be an observable dynamic which could also favor the presence of life”.

This discovery clearly comes at the right time. In just a few months, new, more powerful telescopes will be able to satisfy the curiosity of the astronomers. “We are already preparing observation of the system with the famous JWST, for example, which will be launched into space in 2018 and which should enable us to study these planets in a much more precise way”, explains Michaël Gillon. “In the meantime, we have already obtained some observation time on the Spitzer space telescope to constrain the orbital period of the third planet and confirm its position in the habitable zone. We will also be able to use it to observe the star for a period of around ten days and to try to detect other possible planets. We are also preparing a study programme of the variation in the moments of the transits in order to get their masses by means of many telescopes on the ground, but also a programme on the Hubble space telescope (HST) to try to detect the atmospheres of these planets. In the near infrared, we could already discern certain molecular constituents including water”. And that’s not all. Many things can be learned about the magnetosphere of these planets, or on the characterization of the host star itself; its composition, its activity, its variations in brightness due to its magnetic field or the heterogeneity of its surface, its photosphere, which made it possible to establish its rotation period as 1.4 days compared to 26 days for the Sun. There are many research ideas, and all the study demands so far have been collected and accepted with a lot of enthusiasm. It should not be long until astronomers the world over rush to study TRAPPIST-1. There is incredible excitement which pleases the two researchers and which promises to rapidly accelerate the level of knowledge about this system and others yet to be discovered. “As we found this system by looking at only 50 stars, there is a great chance that they are more numerous and easily detectable. TRAPPIST-1 has ensured that little-studied stars are taking center stage, with their specific behavior and their particular protoplanetary discs etc. A completely new area of research has just been created”, the researchers conclude.