Another great first for James-Webb, NASA’s superpowered space telescope, which began observing last July. Thanks to one of his instruments, the Mirim imager developed by the CEA on this side of the Atlantic in France, James-Webb was able for the first time to detect rocks of comparable size to Earth emitted by an exoplanet, as reported in the press release of the NASA explained. The exoplanet in question is called Trappist-1b; It is part of a rich system of seven terrestrial planets orbiting the star Trappist-1, a tiny red dwarf (its radius and mass are about 11.5% and 8% of the Sun, respectively) located 40 light-years from Earth away near the constellation is Aquarius.
Like Earth, Trappist-1b emits very weak infrared radiation back into space, heated by its star. Miri, the only James Webb imager working in the mid-infrared range, was sensitive to this barely perceptible radiation. More specifically, the teams responsible for these observations – including in France the CEA researcher Elsa Ducrot – used a technique called “photometry of a secondary solar eclipse”. When the planet passes behind its star and is thus obscured by it (secondary eclipse), its infrared radiation disappears, slightly reducing the total amount of light from the system (star and planets). The amount of light derived by subtraction specific to the studied planet is rich in information.