SAINT-EX ― Search and characterisation of exoplanets


The SAINT-EX project is motivated by the fact that it is now possible to reach a precision of 100 ppm (parts per million) on the depth of a planetary transit around a V=6 star with a ground-based, 1-m class telescope thanks to the availability of a new generation of detectors: back-illuminated, deep depletion CCDs. SAINT-EX aims to search for and characterise transiting exoplanets in support of upcoming space missions and by focusing on ultra-cool stars, to enable the detection of small, Earth-size planets. SAINT-EX will be a fully automated telescope.

Supporting ESA-CHEOPS space mission

CHEOPS will have the ability to address unique science goals in exoplanet science. CHEOPS will go beyond a purely mass-radius based characterisation by providing important insights regarding exoplanet atmospheres at visible wavelengths, which will be unmatched by other existing and near-to come facilities. This includes direct measurements of albedos and orbital phase-curves, both of them potentially providing 1 and 2D reflection maps of exoplanets. Accounting for the finite mission duration and stringent constraints on target visibility due to the orbital configuration of CHEOPS, the facility will be heavily oversubscribed. There will likely be hundreds of exoplanets that will be part of the CHEOPS target list, fuelled by RV programmes but also from photometric surveys (TESS, NGTS and others). Pressure will be high on the facility especially because smaller planets and companions on longer orbits will have higher uncertainty on their ephemerides, which will increase the timeframe where the transit is expected. 

SAINT-EX will pre-screen CHEOPS targets by monitoring the transit windows of super-Earth size planets (and larger) orbiting bright stars. This pre-screening will point out the exact transit time (if one occurs), which will 1) tell CHEOPS exactly when to observe, and 2) free the satellite’s queue to the benefit of science goals exploiting CHEOPS’ unique capabilities.

Searching for rocky planets orbiting ultra-cool dwarfs

The recent discovery of TRAPPIST-1 (Gillon et al. 2016, Gillon et al. 2017) suggests that small planets are frequent around ultra-cool dwarfs (M5.5 to M9). This discovery indeed confirms that an untapped population of small planets exists around ultra-cool hosts. The interest in small planets orbiting ultra-cool dwarfs is justified by their enhanced detectability compared to Sun analogues and the unprecedented opportunity they offer for atmospheric characterisation of temperate, Earth-size planets with future facilities such as JWST. The SPECULOOS project, located in Cerro Paranal  (Chile) will start operations later in 2017 and will survey the brightest ultra-cool stars in the Southern hemisphere. The second goal of the present project is to take part to this search and carry out a survey of ultra-cool stars from the Northern hemisphere to search for small, rocky planets with equilibrium temperatures similar to the Earth and Venus.

SAINT-EX will reach the photometric precision to detect down to Mars-size planets orbiting in the habitable zone of the brightest ultra-cool dwarfs.

Follow-up of new exoplanets

SAINT-EX will also be employed to follow-up new exoplanet discoveries visible from the North. This includes new exoplanets from the NGTS, NASA TESS (launch 2018) and PLATO (launch 2024) surveys, among others. Additionally, SAINT-EX could be used in other science areas, such as long-term (and parallel) monitoring of exoplanet host star variability, which will be critical for high-precision transmission spectroscopy with ELTs and JWST.