The greatest discoveries of the JWST will be « those which one obviously cannot expect or imagine »


the James Webb Space Telescope, presented as Hubble’s big brother rather than its successor, still seems on schedule for an Ariane 5 launch at the end of the year. This observatory will show its full potential by observing the first objects formed only a hundred million years after the formation of the Universe, which is today the limit of Hubble’s capacities. The JWST should allow great advances.

Exceptional mission. The James-Webb (JWST, for James Webb Space Telescope) is the largest telescope astronomical never launched into space. This instrument, the result of collaboration between space agencies – Nasa, THAT and ASC – must observe a very wide variety of targets including the most distant visible objects ever recorded. Very dim and almost invisible to the hubble telescope, they are the raison d’être of the James-Webb which should approach as close as possible to the end of the so-called period of dark ages, the phase of inflation which generated the large structures and the first objects ofUniverse. If the James-Webb will be able to see these first objects only a hundred million years after their formation, the holy grail of astronomers, nevertheless he will not be able to see them « light up », at the exit of the dark ages.

NASA trailer for the Webb Space Telescope mission. © NASA

A journey back in time to the grail of astronomers

As Pierre Ferruit, the scientific co-head of the James-Webb mission at ESA, explained to us, the JWST’s greatest discoveries are “ those that we obviously cannot expect or imagine « . What must be understood is that this observatory represents a  » such leap forward for astronomy « , That there will inevitably be discoveries » in all areas of astronomy « . In addition, if the telescope Hubble reaches its limits when it comes to observing objects formed only a few hundred million years after the Big Bang, « this is really where the JWST will show the full extent of its capabilities and bring enormous knowledge to this pivotal period in the history of the Universe, only a few hundred million years after the Big Bang ».

Quite simply, the « Webb » will be the largest astronomical telescope ever launched into space.

The dimensions of the James-Webb are difficult to grasp. Realize, with a height of over 20 meters, a primary mirror of 6.5 meters and a heat shield (sunshade) as large as a tennis court, the « Webb » will simply be the largest. astronomical telescope never launched into space. With such dimensions, its launch can only be done folded to make it fit inside the cap of the Ariane 5 launcher. If it obviously surpasses all those previously launched into space, it is on par with some terrestrial observatories and surpasses all earthly instruments that function in theinfrared, with a gain of 10 to 100!

The deployment of the JWST after its launch by Ariane 5. © ESA, ATG medialab

Iconic images that will be revisited

If the images of Hubble, some of which have become iconic like those of the Nebula of the Eagle or the Deep Fields, have helped immensely in the popularity of theastronomy, no doubt the James-Webb will accentuate this trend. We already know that these iconic images will be revisited by Webb, with new information as a result.

With the Ariane 5 return to flight scheduled for July, the James-Webb will be launched by the end of the year, at best at the end of November, the beginning of December.

The first images are scheduled for June 2022

If a month will be necessary for him to return to his position at point de Lagrange L2, located 1.5 million kilometers from our planet, about four times farther than the Moon, six months will be necessary for those in charge of the mission to put it into service. The first images are scheduled for June 2022. The mirror will be deployed throughout the journey that will take it to L2.

An exceptional promontory for observing the Universe

This point of Lagrange 2 was obviously not chosen at random. It is an exceptional promontory for observing deep space, away from the Soleil and Earth, which should allow the James-Webb to achieve very ambitious scientific objectives. At this distance, the telescope and its four instruments (two of which are supplied by Europe), in the shade of a heat shield, will operate continuously at -253 ° C, a temperature close to absolute zero, fixed at – 273.15 ° C.

You will understand, the main interest of L2 is that the Sun, the Earth and the Moon will be constantly « behind » the sun visor, so that the telescope and its instruments will be constantly in the cold and the dark. As the JWST will accompany the Earth around the Sun, all places in the sky will become observable over periods of at least 50 days. The entire sky will therefore be accessible to astronomers during the year, with the exception of Solar system internal, i.e. the Sun, Mercure, Venus and Earth.

This space observatory is to operate for at least five years. It has enough « fuel » to run for 10 years.

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