Discovered in May 2016 (1) by an international team led by par Michaël Gillon, an astronomer at the University of Liege, the exoplanetary system TRAPPIST-1 has revealed more secrets.
The intensive surveillance of the system using several telescopes, including NASA’s Spitzer space telescope, has not only reinforced the results received previously by the TRAPPIST-Sud telescope in Liege, but has also revealed the presence of four planets in the system bringing their number up to seven. According to the results published in the journal Nature (2), these seven planets are similar in size to Earth and could have liquid water on their surface, particularly in the case of three of them which orbit in the so-called “habitable” zone of their star. TRAPPIST-1 is the system with the biggest number of rocky planets and the greatest number of potentially habitable worlds ever discovered up to the present day. It has reignited the quest for extra-terrestrial life in the Universe.

> Read the press release

Michaël Gillon

Astronomer at OrCA Laboratory
STAR Research Institute
FNRS research associate
More information about Michaël Gillon

Emmanuel Jehin

Astronomer at OrCA Laboratory
STAR Research Institute
FNRS research associate
More information about Emmanuel Jehin

Julien De Wit

Graduated from the Université de Liège
Post-doctoral student at MIT
Earth, Atmospheric & Planetary Sciences

> A trio of Earths 40 light years away?
Astrophysicists from Liege have discovered three Earth-sized planets around a star 40 light years away. These planets could present habitable conditions on their surfaces. In addition, the large telescopes of the future will be capable of studying them in detail and detecting whether or not life exists on them!

> The exoplanets orbiting the TRAPPIST-1 star deliver new secrets.
The international team of astronomers, who revealed the existence of a small, close planetary system, provides additional observations on the composition and atmosphere of two of these exoplanets.

TRAPPIST-1, special poster

NASA has published a special poster for the discovery of TRAPPIST-1.

Download here

The transit method

This is an indirect method for detecting exoplanets. It consists of observing the apparent variation of a star’s light intensity when one of its planets passes between it and an observer. On the basis of calculating this variation, it is possible to gain a whole series of information about the exoplanet: its size, mass, orbit, composition, etc.

TRAPPIST-1, the comic

A story drawn by Sylvain Rivaud alias Lepithec, comics author and illustrator.

> Read the story


The search for exoplanets, in other words planets situated beyond our solar system, began in the 1940s. The first discovery of one of them (or two of them, to be precise) occurred in 1991, but it concerned planets orbiting around a dead star and not a living star like the Sun. In 1995 Swiss astronomers announced the discovery of another exoplanet, spinning round Pegasus 51, situated 40 light years from us. The detection methods are generally indirect ones: perturbations brought about by the presence of the planet are measured. Nonetheless the method known as ‘active optics’ (the surfaces of telescope mirrors are modified several times a second in order to compensate atmospheric turbulence) enabled the first photo of an exoplanet to be taken in 2008.

> TRAPPIST-1 is the name of the exoplanetary system that has the largest number of telluric planets and the largest number of potentially habitable worlds ever discovered.

> TRAPPIST is the name of the telescopes devoted to the detection and characterization of planets located outside our solar system and to the study of and other small bodies in our solar system. (TRAnsiting Planets and PlanetesImals Small Telescope)

> SPECULOOS is the name of the project that aims to detect telluric planets eclipsing some of the smallest and coldest stars in the solar neighborhood (Search for habitable Planets EClipsing ULtra-cOOl Stars). This project is supported by the EU’s European Research Council (ERC).

Publication references

> Gillon et al., Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1, Nature, February 2017

> Julien de Wit et al.,  A combined transmission spectrum of the Earth-sized exoplanets TRAPPIST-1 b and c’, in Nature , 20 July 2016

> Gillon, E. Jehin, et al., Temperate Earth-sized planets transiting a nearby ultracool dwarf star, Nature, May 2016