Between 2015 and 2017, astrophysicistsastrophysicists discovered seven Earth-sized planets around Trappist-1. This star is one of the red dwarfs, the smallest, less massive and less luminous of the stars of the main sequence, and more particularly of the ultracold dwarfs, a class of objects bringing together the cooler red dwarfs and the brown dwarfs, with temperatures between approximately 1900 and 2600°C.
Ultracold dwarfs are numerous but, due to their low brightnessbrightness, Trappist-1 was until recently the only one around which planets had been discovered. The list has just grown, however, as an international team led by Michaël Gillon, professor at the University of Liège (Belgium), has just detected a planet around Speculoos-3.
An analogue of Trappist-1 b, but without companions
The star Speculoos-3, about 55 light years from Earth, has a diameter equal to 12% of that of the SunSunvery similar to Trappist-1 and about 20% larger than JupiterJupiteralthough a hundred times more massive than the orange planet (10% of the massmass of the Sun). For its part, the planet Speculoos-3 has a diameter equal to 98% of that of Earth. There little planetlittle planet goes around its star in just 17 hours, which, despite the relative “coolness” of the star (2,600 °C, compared to 5,500 °C for the Sun), means that Speculoos-3 has a surface temperature estimated at around 280°C.
Furthermore, the planet is probably in synchronous rotation, always showing the same face to its star. These characteristics make Speculoos-3 b similar to Trappist-1 b, with the notable difference that, unlike the latter, the new planet is the only one known in its system.
The relatively strong irradiationirradiation of Speculoos-3 b (16 times more than Earth) combined with radiation infraredinfrared and the small size of its star make this planet one of the exoplanetsexoplanets most promising rocks for the characterization by spectroscopy ofemissionemission with the James Webb Space TelescopeJames Webb Space Telescope (JWST).
Indeed, according to the authors of the study, the observation of only ten eclipseseclipses secondary (when the planet passes behind its star) with the mid-infrared instrument (MiriMiri) and the spectrometerspectrometer low resolutionresolution (LRS) of the JWST would make it possible to have strong constraints on the composition of the planet’s atmosphere (if it has a atmosphereatmosphere) and on the mineralogy of its surface.
“ This planet is an ideal target for the James Webb Space Telescope (JWST), it is even better than the planets of Trappist-1explains Émeline Bolmont, assistant professor in the department of astronomy at the University of Geneva (Switzerland), director of the Center for Life inUniverseUniverse and co-author of the study. The JWST should be able to determine whether the planet was able to maintain an atmosphere despite the proximity of its star, she concludes. If one is found on this highly irradiated planet, this gives good hope that there are also ones on the planets in the habitable zone of Trappist-1 “.
