As the Webb telescope will be operational soon, its first missions included COSMOS-Webb.

Astronomers believe that the Universe originated from the "Big Bang". Between 400,000 and 1 billion years after the Big Bang, the Universe was in a "Reionization Era", in which the starlight of the first generation of stars and galaxies ionized neutral hydrogen atoms to form ionized bubbles near the light sources. COSMOS-Webb will observe more than half a million galaxies with the Near Infrared Camera (NIRCam) and Mid-Infrared Instrument (MIRI) to understand the formation and size of these ionized bubbles.

In addition, Webb will look for the oldest and most distant galaxies that are originating in the early days of the universe. When Webb finds more of these galaxies, we can study them in more details to understand their evolution.

Finally, astronomers use gravitational lensing techniques to estimate the amount of dark matter by exploiting the distortion of light around galaxies. Dark matter is an invisible form of matter that makes up most of the mass of the universe and acts on gravity. COSMOS-Webb will shed light on the distribution of dark matter in galaxies as well as how the stellar content of galaxies evolves with the age of the universe.