The launch of the James Webb telescope (JWST), and especially its deployment spread over 28 days, was announced as “the most complex ever carried out during a space mission”, as confided to us last December Anthony Boccaletti, deputy director at Space Studies and Astrophysical Instrumentation Laboratory (Paris Observatory – PSL). But everything went perfectly.
Installed in the fairing of an Ariane 5 ECA rocket, the 6.2-ton machine took off from the Guiana Space Center (CSG) on December 25, then, once ejected from the fairing where it was carefully folded, flew open like a flower… 22 meters wide! After deploying the solar panels, then the communication antenna, the JWST unrolled the five layers of its heat shield, which allows it to cool the telescope instruments to -233°C, when it will be +80°C on the part exposed to the sun. Then he opened his two mirrors, which are used to capture infrared light coming from the depths of the universe. Since January 12, he has readjusted the 18 fragments of the main mirror one by one so that they combine their power as well as possible.
Five to six months of instrument calibration
In all, 344 points of failure have therefore been avoided, which ensures – in principle – the perfect functioning of the JWST. Everything is now ready for the telescope, the result of collaboration between the American Space Agency (Nasa) and its European (Esa) and Canadian (ECA) counterparts, to begin its scientific mission. All that remains is to insert itself at the Lagrange 2 point (see below), which is 1.5 million km from Earth, its final destination. A last step that can be followed on the NASA website “Where is Webb?”.
The Lagrange point 2 (L2), is located after the Moon. The James Webb Telescope will revolve around this point while following the rotation of the Earth around the Sun, thus taking advantage of its shadow.
NASA / WMAP Science Team
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Ground crews are scheduled to ignite the JWST thrusters at 8:00 p.m. (Paris time) on Monday, January 24. A maneuver aimed at refining its insertion trajectory and correcting the speed of the space telescope. NASA will then open a question and answer session for the general public, who can question it on social networks using the hashtag #UnfoldtheUniverse [Dévoiler l’univers], from 9 p.m.
Then, the engineers will begin the process of aligning the various optical instruments of the JWST as well as a battery of tests ensuring its proper functioning. All of these operations should last about five months, so that observations of the universe will begin at best at the end of June – beginning of July.
From this date, the main mirror made up of 18 hexagonal elements covered in gold, a metal that reflects infrared light particularly well, will point to various parts of the universe that the James Webb aims to reveal. The reflection on the primary mirror will be returned to the secondary mirror, positioned above it, which will in turn return the light to the center of the primary mirror in order to enter the optical system and the four infrared instruments of the telescope.
The American NIRCam camera will be used in particular to look at exoplanets – planets located outside our solar system – thanks to a coronagraph, which makes it possible to mask the light of the stars. The Canadian imager NIRISS will also make images, in support of NIRCam, but also spectroscopy, aimed at finding signatures of the chemical composition of galaxies or exoplanets, or even information on its movement. The European NIRSpec spectrometer, a pure spectrograph, will be used to observe between 50 and 200 objects at a time. Finally, the American-European Swiss army knife MIRI, will make it possible to look in the mid-infrared spectrum, where others will observe the near infrared.
Capturing infrared to go back in time
Watching the infrared spectrum is essential in space exploration since it allows us to go back in time. Because the more light travels through space – the more it “ages” – and the more it “reddens”. In other words, the farther you look into space, the further back in time you go. Thanks to its infrared vision, the JWST will therefore go back in time to -13.5 billion years (Ma), i.e. a few hundred million years after the Big Bang (-13.8 Ma) only!
He will then scrutinize the “dark ages” of the Universe, when the first stars lit up and the first lights were emitted. “The JWST will be 10 to 100 times more sensitive than all existing infrared instruments, so we will go further in time and detect fainter objects better, we will see the first stars and galaxies. their childhood will explain to us what they are today”, confided to us Pierre Ferruit, the scientific manager of the telescope at the European Space Agency (ESA).
Researchers will, for example, try to answer a mystery of astrophysics: why some galaxies have not created stars for billions of years, when they still have enough matter and gas to do so? Without this process, our universe would be very different: it would house more massive galaxies, with more stars and, logically, more planets. The space telescope will also observe the Orion Nebula, which is “only” 1,344 light-years from Earth, a “nursery” of stars where some of them, of a size comparable to our Sun, are forming. By looking at Orion, scientists hope to better understand how our solar system was born, and what were the ingredients at the start of its formation.
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Similarly, the JWST should be able to characterize the atmospheres of certain exoplanets, including gas giants, in order to know the molecules they house or their temperature. He will also point his instruments towards “super Earths”, these giant telluric exoplanets that are still very poorly understood. He will be particularly interested in those that are in the famous “habitability zone”: neither too close nor too far from their star, which allows the presence of liquid water, essential to life as we know it. on earth. The first results of these observations should be published between the end of June and the beginning of July 2022.
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