SPECULOOS
The SPECULOOS (Search for habitable Planets EClipsing ULtracOOl Stars) project uses an array of robotic telescopes to observe the smallest, coolest stars of the solar neighborhood in search of potentially habitable planets suitable for atmospheric studies.
The ability of the transit method to detect and study in detail small rocky planets, like the Earth, is all the stronger when the host star is small, cold, and close. Indeed, for the same planet, the smaller the star, the larger the fraction of its surface hidden by the planet or by its atmospheric limb during the transit. The smaller and colder the star, and therefore the less luminous it is, the greater the contribution of the planet to the light measured by our instruments. And the closer the system is, the more precise our measurements are. Taking these elements into account, we can estimate that the detection and study of an atmosphere of an exoplanet similar to the Earth (size, mass, atmosphere, temperature) in transit is only possible if its star is an ultra-cool dwarf. This category includes stellar objects whose surface temperature is less than half that of the Sun. These objects have respectively a mass and a radius of less than 10% and 15% of those of our star. If their mass is less than ~7% of that of the Sun, they are not stars, but brown dwarfs, i.e. objects that form like stars but do not transform hydrogen into helium in their core (nuclear fusion).
The goal of SPECULOOS is to observe the ~1000 ultra-cool dwarfs that are sufficiently close and bright to allow the atmospheric study of a possible habitable Earth-sized exoplanet. About 90% of these objects are very low mass stars, and the rest are brown dwarfs. To be clear, the goal of SPECULOOS is to detect transiting exoplanets around as many of these stars as possible, not to study their atmospheres. For that, an extremely powerful space telescope like the James Webb Space Telescope is needed.
SPECULOOS was initiated and is directed by Michaël Gillon, and involves the whole EXOTIC team. The project saw the light of day in 2011 as a prototype on the TRAPPIST-South telescope in Chile (Gillon et al. 2013). This prototype led to the discovery of the extraordinary TRAPPIST-1 (= SPECULOOS-1) planetary system composed of seven Earth-like planets orbiting an ultra-cold dwarf star 40 light years away (Gillon et al. 2016, 17). After this prototype phase, the project itself started its operations in 2019. Other institutions than ULiege are participating: the University of Cambridge, MIT, the University of Zurich, the University of Birmingham, and the University of Bern. The project operates six robotic telescopes of 1m aperture (diameter of the primary mirror). Four of them are located in Chile, one in Tenerife, and one in Mexico. In 2022, it discovered a new potentially habitable planet around another ultra-cold dwarf named SPECULOOS-2 (Delrez et al. 2022). Many others should follow...
SPECULOOS is funded by the European Research Council, the FNRS, the University of Liege, the Walloon Region, the SNSF, as well as by the Balzan Prize, the MERAC Prize, Francqui, Simons, and Heising-Simons Foundations.
