Core science motivation and goals
Today, about 3700 exoplanets are known. Many of them fall into new classes unlike any of the planets of the Solar System, e.g., ’hot Jupiters’, ’mini-Neptunes’ and ’super-Earths’ (planets <10 Mearth). However, this sample currently lacks exoplanets resembling the terrestrial planets of our own Solar System. It is the goal of PLATO to find these planets and to provide the first catalog of potentially habitable planets with known mean densities and ages. While ages constrain formation and evolution scenarios, mean densities provide information on the physical nature of planets (gaseous, icy, rocky, or a mixture ?). These constraints require accurate and precise planetary radii, masses and ages determination. To this end, PLATO will combine three approaches.
The two first rely on ultra-high precision photometry which will provide light curves to:
- determine the planetary radius relative to the host star’s radius, and the system’s orbital parameters through the transit method,
- determine the stellar parameters and properties thanks to asteroseismology.
Moreover, the PLATO mission consortium will coordinate the world-wide observational effort in terms of spectroscopic follow-up needed to:
- confirm the transiting planets, and provide their masses using radial velocity.
The PLATO mission goals include the determination of planetary radii with an accuracy of 3 % and masses with a 10 % accuracy for planets orbiting stars with a visual magnitude brighter than 10. For terrestrial planets in the habitable zone of solar-like stars, PLATO will be the first mission able to provide such highly accurate bulk planet parameters. Another prime goal of the PLATO mission is to determine accurate ages of planetary systems (10 % accuracy for bright solar-like stars). Since planet formation is fast, the age of a planetary system can be assumed to be basically equal to the age of its host star. PLATO will provide ages for a large number of planetary systems through asteroseismology.
Core Stellar Science
To improve the accuracy of planet parameters, it is essential to improve our description of low-mass stars in general. This involves improving the stellar models in terms of transport mechanisms, chemical mixing, rotation, magnetism, etc., to eliminate the dependency of the estimated parameters on underlying physical assumptions used in stellar modelling. While the masses and radii of stars are weakly model-dependent, the age estimates remain strongly model-dependent (Lebreton et al. 2014a & b). A better understanding of the physical processes involved in stellar evolution and their description in stellar models is therefore a key requirement of PLATO. Ground-based data, Gaia results and asteroseismology from PLATO will be combined into one consistent analysis for a large number of stars of various masses and chemical compositions.
In that context, the core stellar science work package (a.k.a. WP120) plays a key role in reaching the mission’s science goals : its responsibility is to specify the methods for the determination of accurate and precise stellar parameters for all the dwarf and subgiant stars later than spectral type F5 from the photometric light curves obtained from the instrument. In other words, WP120 will be in charge of providing the specifications for the PDC to deliver seismic spectra (data products DP3), surface rotation and activity indicators (DP4), radii, masses and ages (DP5) for the hundreds of thousands of low-mass stars of the PLATO core programme.
Links
ESA Mission page
PLATO website
PLATO Science Management website