In this second module we will focus on the detection of exoplanets. Together we will discover three methods for detecting extrasolar planets. (1) Radial velocities, which allowed the first detections of hot Jupiters. (2) Astrometry, a method that the Gaia satellite has greatly contributed to boosting. (3) Direct imaging, the only way to really see planetary companions. Don't be scared off by the mathematical approach used to describe these methods. A general understanding is sufficient to follow the next few weeks of the course.

For this third module, we remain in planet detection. However, this time we will explore the specific case of a planet being seen nearly edge-on and transiting its star. The observation of exoplanet eclipses (transits and occultations) provides us with a wealth of parameters and is currently the most powerful technique to study the structure and other intrinsic properties of planets. In this module, you will therefore have the opportunity to discover mainly how to apply the transit method, but also, at the end of the module, the main outcomes that have been obtained through the use of the transit method.

Now let's dive into statistics! In this module, we will be interested in the statistical properties of planetary systems. We have chosen to use a chronological approach to do so. First of all, you will discover the first results of the radial velocity programs which unveiled the great diversity of planetary systems. We will then compare these results with those obtained more recently by the transit surveys and the most recent radial velocity surveys. The statistical results of these research programs have brought to light a multiplicity of discoveries around exoplanets. You will have the pleasure of discovering them throughout this module.

For this fifth module, let's continue our exploration of statistical methods! We will continue to discover the properties of the exoplanetary systems that have been detected so far. You will have the opportunity to understand the link between the properties of the planets and the mass of the central star. We will also see in more detail the dynamics of multiplanetary systems, how planet-planet interactions are translated and, in particular, what are the parameters that influence the stability of systems.

Let us leave now the statistical analyses to go and look at the properties of the surfaces and atmospheres of exoplanets. In the previous modules, we have seen that radial velocity measurements combined with transits observations allow us to have access to the average density of exoplanets. We could thus put some constraints on the internal structure of the objects. Although only a few very specific systems (young and massive planets with large separation) have been imaged so far, spectroscopic measurements and subtle strategies of observation of transiting and non-transiting systems allow us to know the characteristics of planetary surfaces and atmospheres. This is all we will see together for this penultimate module.

For this last part of the course, let's continue and complete our exploration of the atmospheres of exoplanets. This module is in fact an update of the course. It integrates the new insights obtained on exoplanet atmospheres since 2014 (date of the first edition of this MOOC). Actually, the content of these last videos is very close to what you would get if you were attending a review on the subject at a real scientific conference. We hope you will enjoy this journey through the different layers of the atmosphere of exoplanets!