A little over a week ago, the Nasa published the first images made by the telescope James Webb (James Webb Space Telescope – JWST), the most powerful space observatory in the world. The project is the result of an immense international collaboration and integrates Canadian and European resources. More than 10,000 people worked on the project, which had a final budget of around US$10 billion, or more than 54 billion reais.
The JWST has two main scientific missions. First, explore the earliest stages of cosmic history, traveling over 13 billion light-years from Earth to reflect images of distant galaxies. Its second major objective is the discovery of exoplanets, ie planets outside the solar system. He will also study the potential for life on these worlds by studying their atmospheres.
Scientists began planning a successor to the Hubble Space Telescope in the 1990s. Construction of the JWST began in 2004, and its launch has been repeatedly delayed. It was originally planned for 2007 and then for 2018, but it was not launched until December 2021. The mission is planned to last at least five years.
James Webb orbits the Sun about 1.5 million kilometers from Earth, still far from the galaxies he plans to study. Unlike the ultraviolet and visible light in which Hubble primarily operates, the longer wavelengths of infrared penetrate dust more easily, and it is in this range that the new station aims to operate.
Infrared also allows scientists to see farther through a phenomenon called ‘redshift‘: Light from more distant objects is stretched, as the universe expands, towards the infrared end of the spectrum.
To capture these images, Webb needs a large reflective area. A telescope’s sensitivity, which determines how much detail it can see, is directly related to the size of the area of the mirror that collects the light.
The centerpiece of the telescope is its massive primary mirror, a concave structure 6.5m wide and made up of 18 smaller hexagonal mirrors. Each segment weighs approximately 20 kg, made of gold-coated beryllium, optimized to reflect infrared light from the far reaches of the universe. The JWST even has a convex secondary mirror and a tertiary mirror which removes the distortions created by both.
The engineering team needed to develop a structure that could be folded to fit a rocket and unfolded after launch. Each of the 18 mirror segments is 1.32m in diameter. The hexagonal shape allows their junction to approach a circular shape – with edges that fit together without gaps – to focus the light rays as much as possible and generate images that are closer to reality.
To observe the most distant stars and galaxies, astronomers need to see the infrared light emitted by these hot objects. If the mirror of this telescope were the same temperature as the Hubble Space Telescope, for example, the weak infrared light would disappear.
Thus, the Webb must be very cold, around -220°C, be able to withstand freezing temperatures while maintaining its shape. Beryllium is a light and strong metal, capable of remaining stable under wide temperature variations. For this reason, it is the material chosen to serve as the basis for the mirrors.
The space telescope is still protected by a kind of five-layer umbrella, shaped like a kite the size of a tennis court. Their membranes are composed of capton, a heat-resistant material that is stable over a wide temperature range, since the side of the structure that will face the sun can reach 110°C. A space shuttle is also attached to the main structure, containing power, propulsion, communication, guidance, heating, and data manipulation systems.
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