Target prioritization routines for CHEOPS observations

Short Description

Starting point / motivation

Both exoplanet missions and ground-based facilities revealed the existence of a great variety of planets, particularly for intermediate-mass planets (sub-Neptune, super-Earth) with masses between 2 and 14 MEarth, which present a large spread in density. These planets are the primary target of CHEOPS, the first S-class ESA mission, which aim is the detection of shallow transits of low- and intermediate-mass planets orbiting bright stars.

Contents and goals

Typical CHEOPS targets will be systems hosting planets already detected by radial velocity, for which CHEOPS will search for transits, and systems hosting planets detected with the transit method by other facilities (e.g., NGTS and TESS), but for which the measurement of the radius requires a considerable improvement.

Hundreds of possible CHEOPS targets are foreseen, but the time constrained nature of CHEOPS observations will not allow to observe them all. It is therefore necessary to construct a target prioritization strategy.


This is the primary aim of this project. We propose to build a method and tool capable of providing a fast rough planet characterisation, based on theoretical models, for CHEOPS targets. We recently developed a method that allows one to provide a first characterisation of the atmosphere of an intermediate-mass planet provided only its transit radius.

The method allows one also to infer the minimum planetary mass, while the maximum mass can be inferred from considerations on planetary density and formation. We will compute a large grid of hydrodynamic models of the upper atmosphere of planets considering a parameter space composed by: planetary mass, radius, equilibrium temperature, and stellar high-energy input flux.

We will use the grid of models to compute planet atmospheric evolution tracks, taking into account realistic levels of the initial high-energy stellar flux. The tracks will have an unprecedented resolution and will be among the first ones taking into account the full extent of possible high-energy stellar input.

The models and tracks will be tested against intermediate-mass planets with measured mass and radius to test/improve the predictive power of the grids. We will use the grids to design a characterisation scheme for the planets discovered with the radial velocity method and with transits detected by CHEOPS.

Expected results

The scheme will be made available through a public web tool and will be used to prioritize either further CHEOPS observations or follow-up observations aiming at a full atmospheric characterisation.

We will use our developed innovative method to design also a characterisation scheme for planets discovered with the transit method by other facilities, hence possible CHEOPS targets. Also these tools will be made available through a public web site.

We will finally explore possible wider implications of our findings to study the feasibility of a large-scale usage of the tools developed within the project to infer the range of planetary masses for Kepler, NGTS, and TESS intermediate-mass planets with the aim of deriving planetary mass functions.

Project Partners


Austrian Academy of Sciences


Contact Address

Austrian Academy of Sciences
Dr. Luca Fossati
Schmiedlstraße 6
A-8042 Graz