About 19.3% of the 4001 exoplanets confirmed to date were discovered with the technique of the radial velocity (from https://exoplanets.nasa.gov/). This method consists in using time series of spectroscopic observations in order to measure the periodic oscillations of the position of stars due to the presence of orbiting exoplanets. In fact, in a planetary system both the planets and the
The discovery of the first planet orbiting around another star occurred in the 1995, thanks to the astronomers Michel Mayor and Didier Queloz. This discovery set a milestone in astronomy both because it was the first observational confirmation of the existence of planets orbiting around other stars (in this case 51 Pegasi), and because of the nature of this exoplanet. It
The NASA satellite Transiting Exoplanet Survey Satellite (TESS) it’s one of the most effective telescopes to search for exoplanets. TESS is designed to find exoplanets with the transits method, e.g. by observing the periodic occultations of stars by their planets during their orbits. To date, about 27% of the exoplanets discovered with TESS belong to the class of the sub-neptunians. These planets have a
In the last years, stars of spectral class M (which are stars with effective temperatures between 2400 and 3700 K and masses between 0.08 and 0.45 solar masses) have been extensively observed for the search of exoplanets. This both because they are the most abundant class of stars in the Galaxy, and because the low star/planet mass ratio, compared to
The exoplanetary systems discovered so far (3212 systems with a total of 4331 exoplanets, as reported by https://exoplanets.nasa.gov/ on January 21st 2021) show a great variety of systems architecture, with some configurations which are completely different than that of our Solar System. This variety of architectures is a challenge for studies of the planetary formation process and all mechanisms that contribute in
A “transit” occurs when we observe a planet moving across the disc of its star. Thus, during the transit the planet obscures a small portion of its star, slightly reducing its luminosity. While in the Solar System the only planets we can observe transiting in front of the Sun are Mercury and Venus, transits is still the most efficient method
Ultra-hot Jupiters are gaseous planets orbiting at close distances from their central stars, with rotation periods shorter than 3 days. Their atmospheres are thus heated, more than 2000 degrees, by the incident radiation emitted by the central star. For this reason, the atmospheres of ultra-hot Jupiters shows peculiar properties compared with planets of other types. For instance, they are affected
The mechanisms involved in the formation of planets are still not completely understood. The most widely accepted model that describe the formation of gaseous planets is the core-accretion model. In this paradigm, the formation of these planets starts with the formation of a large rocky core by the coagulation of planetesimals, followed by the accretion of a large gaseous envelope
Some of the exoplanets known so far belong to classes that do not exist in our Solar System. For instance, the class of the Hot Jupiters, i.e., gaseous giant planets orbiting at close distances from their stars (typically less than 0.5 AU, Astronomical Unit, where a 1 AU is the average distance between Sun and Earth, about 150 million km).
Despite theoretical models predict a large abundance of Earth-like planets in our Galaxy, the family of the 4284 planets discovered so far (updated at 2020/9/25, credits: NASA) counts relatively a few of such a planets. This is clearly an observational bias, due to the fact that the methods used to detect planets are not sensitive to small planets. For this
