James-Webb: what we expect from the giant space telescope

NASA will send a new space telescope called James-Webb into space on December 18. It will take over from Hubble, which has been in service since 1990. A hundred times more sensitive than its ancestor, it has a larger mirror and capacities designed for the study of the deep universe and exoplanets. It will orbit 1.5 million km from Earth.

A giant among telescopes

The James-Webb Space Telescope (JWST) will be the largest telescope ever launched, by far. Weighing 6.5 tonnes on the scale, it deploys a primary mirror 6.5 m wide (2.4 m for Hubble) made up of eighteen hexagonal mirrors. Its thermal shield, which protects it from the heat and sunlight, is 22 m long and 10 m wide, about the size of a tennis court.

Where will it be positioned?

The launch will take place aboard an adapted Ariane 5 rocket. Once the mirror is folded back on itself, it just holds (the maximum width is 5.4 m). The James-Webb will take its freedom at an altitude of 1,400 km, twenty-seven minutes after takeoff. Before embarking on a four-week journey to its destination: the Lagrange L2 point, 1.5 million km from Earth. At this point, the gravity fields of the Earth and the Sun balance each other and an object of negligible mass can remain motionless with respect to these two reference points.

What are its main missions?

“We will be able to capture the light of the first galaxies formed in the Universe,” enthuses astrophysicist Thomas Zurbuchen (Nasa). But also much better to study the extrasolar planets: “The question of the origins of life worries us all. With the JWST, we will not only study the orbits of extrasolar planets, but also their chemical composition. Not to mention the observation of our own solar system. “We expect to be surprised. »

For Antonella Nota (Esa, the European space agency): “With a hundred times more sensitivity than Hubble, we can imagine what we are going to find. "She gives an example, in the pillars of creation", famous star nursery and one of the most famous images of space, the gas hides the nascent stars: "In the infrared, the telescope will be able to all detail them. It will be a space data paradise. »

What are his tools?

The telescope is equipped with several instruments installed in a structure fixed behind the main mirror: the NIR-Cam (camera for the near infrared), the NIR-Spec spectrometer (observation of very distant galaxies and compact sources), the camera/spectrometer Miri (exoplanets and first galaxies) and the near infrared imager Niriss.

How long ?

Five years at the base, but the JWST carries enough fuel to rectify its position for at least a decade. Hubble is still working after thirty years of service. But, if we have done maintenance on Hubble (which crosses at an altitude of 600 km), reaching the JWST will be impossible.

Who is the boss ?

The James Webb Telescope is a NASA device, but it was developed with the help of the European Space Agency (Esa) and the Canadian Space Agency.

It's for when ?

With nearly fifteen years behind the initial schedule, the James-Webb is no longer within a week. But still. Announced in the spring for October 31, the launch is now scheduled for December 18. “Then we will have thirty days of terror until it is well positioned”, jokes (halfway) Thomas Zurbuchen. Once in place, the tests will begin and it will be necessary to wait until the telescope is perfectly cooled so that it is operational. The telescope will deliver its first images only between four and seven months after its departure.

But who is James Webb?

The telescope is named in honor of the second administrator of NASA, from 1961 to 1968. James Edwin Webb (1906-1992) had a crucial role in the success of the Apollo missions. Despite recent controversies, the name will not be changed.