SPECULOOS Southern Observatory

The brilliant luminosity of most stars makes it extremely difficult to spot Earth-sized planets in orbit around them. Smaller, dimmer stars, however, can offer a more accessible target for planet-hunting astronomers and permit the detailed characterisation of any planets found.

The Search for habitable Planets EClipsing ULtra-cOOl Stars (SPECULOOS, its name inspired by the sweet treat) is a project sited at ESO’s Paranal Observatory in Chile’s Atacama desert (there is a sister project in the northern hemisphere). Its mission is to detect terrestrial exoplanets around nearby ultracool stars — of spectral type M7 and later — and brown dwarfs. The facility at Paranal, called the SPECULOOS Southern Observatory, comprises four robotic telescopes of Ritchey-Chrétien design, each with a one metre primary mirror and cameras that are highly sensitive in the near-infrared. While this radiation is slightly beyond what human eyes can detect, it is the primary emission from ultracool stars and brown dwarfs. The telescopes are named after four of Jupiter’s moons: Io, Europa, Ganymede and Callisto.

The forerunners to SPECULOOS are the two TRAnsiting Planets and PlanetesImals Small Telescopes (TRAPPIST) — one at ESO’s La Silla Observatory in Chile and another at Oukaïmden Observatory in Morocco. SPECULOOS will survey ten times as many red dwarfs as TRAPPIST does, and it it is expected to discover at least a dozen systems similar to TRAPPIST-1, which was recently shown to contain at least seven Earth-sized worlds, the most discovered in any system at the time of writing.

SPECULOOS aims to find the most suitable terrestrial planets for detailed atmospheric characterisation — including the potential detection of biosignatures — by future giant observatories, such as ESO’s 39-metre Extremely Large Telescope and the NASA/ESA James Webb Space Telescope.

SPECULOOS is a project led by the University of Liège, Belgium (project leader: Michaël Gillon) and carried out in partnership with the University of Cambridge, UK the University of Birmingham, UK the Massachusetts Institute of Technology, US the University of Bern, Switzerland, the Canary Islands Institute of Astrophysics, Spain and the European Southern Observatory.

Science goals

The mission for SPECULOOS is to detect terrestrial planets as they transit across small, cool stars in the solar neighbourhood, leading to a tiny, regular dimming in the star’s brightness. Exoplanets discovered by this method can be studied in great detail. This includes making precise measurements of their orbital parameters, mass and radius, and the analysis of their possible atmospheres.

While only large exoplanets can currently be studied in detail, powerful future telescopes will have the capability to perform detailed studies of Earth-like exoplanets around small, dim nearby stars. Theory predicts that these ultracool stars should host a large population of close-by, potentially habitable exoplanets. SPECULOOS is therefore designed to detect such planets orbiting in the habitable zone around the nearest 1000 ultracool stars and brown dwarfs, and to make it possible to explore the diversity of atmospheres and climates on these exoplanets and search for traces of biological activity.

More about SPECULOOS

• Read more about this telescope on the SPECULOOS website