Science

The James Webb Space Telescope arrives at its destination, its work will finally begin

The launch of the James Webb Telescope (JWST), and especially its deployment over 28 days, was announced as “the most complex ever carried out during a space mission”, as Anthony Boccaletti, deputy director of Space Studies, told us last December. Spatial. 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 lifted off from the Guiana Space Center (CSG) on December 25 and, once ejected from the fairing where it was carefully folded, opened like a flower. 22 meters wide! After unfolding the solar panels, then the communication antenna, JWST unrolled all five layers of its heat shield, allowing it to cool the telescope’s instruments to -233°C, when it will be +80°C on the exposed side. to the light. Sun. It then opened its two mirrors, which are used to capture infrared light coming from the depths of the universe. Since January 12, he has readjusted one by one the 18 fragments of the main mirror so that they combine their power as best as possible.

Five to six months of instrument calibration

In total, 344 failure points have been avoided, which ensures, in principle, the perfect operation 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 into Lagrange point 2 (see below), which is 1.5 million kilometers from Earth, its final destination. One last step that can be followed on the NASA website “Where’s Webb?”.

Lagrange point 2 (L2), is located after the Moon. The James Webb Telescope will rotate around this point as it tracks the Earth’s rotation around the Sun, taking advantage of its shadow.

NASA/WMAP science team

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Ground crews are scheduled to fire the JWST thrusters at 8:00 pm (Paris time) on Monday, January 24. A maneuver intended to refine its insertion trajectory and correct 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 media using the hashtag #UnfoldtheUniverse. [Dévoiler l’univers], starting at 9 p.m.

Then, the engineers will begin the process of aligning the different optical instruments of the JWST as well as a battery of tests that guarantee their correct operation. All these operations should take about five months, so observations of the universe will start at best in late June or early July.

As of this date, the main mirror made up of 18 hexagonal elements covered in gold, a metal that reflects infrared light particularly well, will point out the different parts of the universe that the James Webb aims to reveal. The reflection from the primary mirror will be returned to the secondary mirror, placed on top of it, which in turn will return the light to the center of the primary mirror to enter the telescope’s optical system and four infrared instruments.

The American NIRCam camera will be used in particular to observe exoplanets, planets located outside our solar system, thanks to a coronagraph, which makes it possible to mask the light of the stars. Canadian imager NIRISS will also generate images, in support of NIRCam, but also spectroscopy, aimed at finding signatures of the chemical composition of galaxies or exoplanets, or even information about their motion. The European NIRSpec spectrometer, a pure spectrograph, will be used to observe between 50 and 200 objects at a time. Finally, the US-European MIRI Swiss Army Knife will allow one to look in the mid-infrared spectrum, where others will look in the near-infrared.

Infrared capture to go back in time

Observing the infrared spectrum is essential in space exploration as 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 more you look into space, the further you go back in time. Thanks to its infrared vision, the JWST will go back in time to -13.5 billion years (Ma), that is, a few hundred million years after the Big Bang (-13.8 Ma) only!

It will then peer into the “dark ages” of the Universe, when the first stars ignited and the first lights emitted. “JWST will be 10 to 100 times more sensitive than all existing infrared instruments, so we will go further back in time and better detect fainter objects, see the first stars and galaxies. Their infancy will tell us what they are today.” “, confided Pierre Ferruit, scientific director of the telescope at the European Space Agency (ESA).

The researchers will try, for example, to answer a mystery in astrophysics: why have some galaxies 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 are forming, of a size comparable to that of our Sun. When observing Orion Scientists hope to better understand how our solar system was born and what the ingredients were at the beginning of its formation.

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Similarly, the JWST should be able to characterize the atmospheres of certain exoplanets, including gas giants, to learn about the molecules they harbor or their temperature. It will also point its instruments at “super-Earths,” these giant telluric exoplanets that are still poorly understood. You will be especially interested in those that are in the famous “habitable zone”: neither too close nor too far from their star, which allows the presence of liquid water, essential for 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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