Exoplanets are by definition located outside our solar system. The search for extrasolar planets is a real
challenge for humanity, the underlying question that scientists are trying to answer is "are we alone in the Universe?".
Since the first discovery of extrasolar planets in 1995 (51 Pegasi b), a large number of space projects such as HARPS (2003), CoRoT (2006), Kepler
(2009), JWST (2018) to Darwin (2020) have obtained funding.
Until 2020, the methods used to find exoplanets, are indirect methods (effect of
transit effect on the radial velocity, microlens effect ...), that is to say that exoplanets are detected only by the effects that it induces
on their star. But from 2020, with the DARWIN space project, all humanity will see an extrasolar planet directly and perhaps a exoterre.
How to detect exoplanets?
Transit (periodic micro-eclipse) occurs every time the planet passes between the star and the observer.
At that time, the planet obscures some of the light from the star, producing a detectable periodic dimming. This remarkable idea is used to detect
the planet and directly determine its size and its orbit. The diameter of Jupiter is 10 times smaller than the Sun, Jupiter mask so 1% of the
luminosity of the Sun as it passes in front of a distant observer. Earth it is 100 times smaller than the Sun, so do mask 1/10000th of its brightness.
How to see exoplanets?
With Darwin, we'll see the planet or rather its atmosphere
that reflects light from its star. Any light that is perfectly aligned with the telescopes (that of the star) will be extinguished and so the
planet can be seen without being dazzled by the nearby star.
What are the biosignatures that will reveal the presence of life on distant exoplanets?
By analyzing the spectrum of light from the atmosphere of a planet, it is possible to detect the presence of chemical compounds such as carbon
dioxide (CO2), water (H2O), ozone (O3), oxygen (O2) or other ionic assembly, and therefore no organic compounds based on a carbon skeleton. CO2
in large quantities and the water would be the signature of photosynthetic activity. Oxygen has a
specific feature. This aggressive atom may not remain in a gaseous envelope around a planet because it binds very easily with metals and rocks,
to make oxides. If there is oxygen in quantity around a planet that means biotic phenomena exist.
Astronomy - The curiosity that characterizes humanity, has enabled man to understand the major astronomical phenomena and it now gives a dramatic sense stronger what is happening before our eyes.
« It is entirely possible that behind the perception of our senses, worlds are hidden of which we are unaware. »
Albert Einstein (1879-1955), Nobel Prize in Physics in 1921 for his interpretation of the photoelectric effect.