Again the marvelous Spaceship from gendragon EXOPLANET - An exoplanet (or extrasolar planet) is a planet orbiting a star different from the Sun (the "exo" prefix means "outside" in Greek). Up until now, one has found mainly gas giant planets, which are easier to detect than telluric planets. However, due to the increasing sensitivity of the detection methods, one already begins to observe the first planets of sizes comparable to the Earth. There are one hundred billion stars in our galaxy, and the observable universe contains at least one hundred billion galaxies. In addition, we know that there are some planetary systems around other stars, even if today we do not know their exact frequency of occurrence. It is hard to believe that the conditions and the processes which led to the emergence of life on Earth three billion years ago were not at work on other planets outside the Solar System. These conditions are, certainly, quite strict. For instance, the necessary existence of liquid water requires that the temperature of the planet be neither too high nor too low. Similarly, if its mass is too large, the planet will become a gaseous planet with an atmosphere made essentially of hydrogen and helium. In such conditions, the chemical reactions of life cannot occur. We think that other conditions are necessary, as, for example, a not too frequent bombardment by asteroids. Indeed, such destructive impacts can make the life process start from scratch again. The presence of Jupiter probably helped to maintain life on Earth. Jupiter deflected a lot of meteorites from the Earth at the beginning of the formation of the Solar System. The communication with possible inhabitants of an exoplanet require that (1), these inhabitants are sufficiently developed (both from an intellectual and a technological point of view), and (2), they want to communicate. If we were trying to contact them, a first step would be to send signals in different wavelengths (visible, infrared, radio,...). These signals should be strongly different from natural signals. The researchers of the SETI (Search for Extraterrestrial Intelligence) program have proposed criterion for this : the signals resulting from natural processes have a high product length-frenquency width compared to the limit fixed by the laws of physics (the uncertainty principle). Conversely, the detection of a signal for which this product is close to the limit would be a remarkable event, likely to draw attention. We will not discuss here what one would say in this conversation ; we only note that such a communication requires a long time compared to the duration of a human life. Indeed, the time necessary for a message exchange would be twice the time of the propagation of light between Earth and the exoplanet, i.e. at least nine years if there was a planet around Proxima Centauri (the closest star to the Sun), or one hundred years in the case of 51 Pegasi. Thanks Magik