CHEOPS: A Transit Photometry Mission for ESA's Small Mission Programme (1305.2270v1)

Abstract: Ground based radial velocity (RV) searches continue to discover exoplanets below Neptune mass down to Earth mass. Furthermore, ground based transit searches now reach milli-mag photometric precision and can discover Neptune size planets around bright stars. These searches will find exoplanets around bright stars anywhere on the sky, their discoveries representing prime science targets for further study due to the proximity and brightness of their host stars. A mission for transit follow-up measurements of these prime targets is currently lacking. The first ESA S-class mission CHEOPS (CHaracterizing ExoPlanet Satellite) will fill this gap. It will perform ultra-high precision photometric monitoring of selected bright target stars almost anywhere on the sky with sufficient precision to detect Earth sized transits. It will be able to detect transits of RV-planets by photometric monitoring if the geometric configuration results in a transit. For Hot Neptunes discovered from the ground, CHEOPS will be able to improve the transit light curve so that the radius can be determined precisely. Because of the host stars' brightness, high precision RV measurements will be possible for all targets. All planets observed in transit by CHEOPS will be validated and their masses will be known. This will provide valuable data for constraining the mass-radius relation of exoplanets, especially in the Neptune-mass regime. During the planned 3.5 year mission, about 500 targets will be observed. There will be 20% of open time available for the community to develop new science programmes.

Overview of CHEOPS: A Transit Photometry Mission

The paper "CHEOPS: A Transit Photometry Mission for ESA's Small Mission Programme" presents a comprehensive analysis and rationale for the ESA's CHEOPS (CHaracterizing ExOPlanet Satellite) mission. The mission is poised to significantly enhance the precision of exoplanetary characteristic measurements, with a specific focus on determining the radii of exoplanets that have been previously identified through radial velocity methods.

Mission Objectives

The primary goal of the CHEOPS mission is to measure the radii of exoplanets in the super-Earth to Neptune mass range with unprecedented accuracy. With its ability to perform ultra-high precision photometric monitoring, CHEOPS targets bright stars already known to host exoplanets, facilitating precise determinations of planetary radii. Consequently, this mission will refine the mass-radius relationship for a range of exoplanets, offering clearer insights into their structural compositions and possible formation mechanisms.

The satellite's two key target categories include:

1. Bright stars with recognized planets from radial velocity surveys.
2. Bright stars with known transiting planets identified by ground-based transit searches.

Scientific Implications

By integrating the precise measurements of planetary radii obtained through transit photometry and existing mass estimates from radial velocity techniques, CHEOPS will enable detailed determinations of exoplanet bulk densities. Such data will significantly contribute to our understanding of exoplanetary compositions, including the potential existence of gaseous envelopes and rocky cores. These insights hold profound implications for models of planetary formation and evolution, particularly for planets in the super-Earth and Neptune-size range.

In addition, CHEOPS will facilitate the paper of planetary atmospheres over a diverse range of masses and stellar proximities. By identifying the presence of significant gaseous atmospheres, CHEOPS will further elucidate critical mass parameters vital for runaway gas accretion in planetary core formation.

Methodological Details

The mission's instrumental capacity is centered around a 30 cm aperture reflecting telescope, designed to achieve stellar photon noise-limited precision. CHEOPS will orbit in a Sun Synchronous Low Earth Orbit, optimizing thermal stability and observing conditions. Targeting stars anywhere in the sky, it can cover up to 50% of the entire celestial sphere with consecutive observation durations exceeding 50%.

CHEOPS is equipped to detect Earth-size planetary transits with a signal-to-noise ratio of 10, achieving photometric precision of 10 ppm in 6 hours. The mission is expected to observe approximately 500 targets over its planned 3.5-year duration, with 20% of observing time designated for community-proposed scientific agendas.

Future Prospects

CHEOPS serves as a precursor to more advanced spectroscopic studies of exoplanet atmospheres by aligning its findings with subsequent high-precision spectro-photometry efforts using facilities like the E-ELT and JWST. This alignment is crucial for advancing inquiries into super-Earth characteristics and their habitability potential.

Overall, the CHEOPS mission represents a significant stride in the precise characterization of exoplanets, set to provide foundational data that furthers the understanding of planetary science. It positions itself not only as a pivotal mission for exoplanetary radius determination but also as a cornerstone for future theoretical and observational advances in the field of exoplanetary studies.