Sciences. James-Webb Space Telescope ready to take off

The countdown has begun. In less than a month, on December 18, an Ariane 5 rocket will take off from the Kourou base in French Guiana, with the most powerful space telescope ever created on board. Intended to take over from Hubble, overtaken by breakdowns and the age limit (it has been operational since 1990), the James-Webb Space Telescope should usher in a new era of astronomical observation.

Why is it an event?

Because this telescope has been awaited by astronomers for almost twenty years. In development since 1996, the James-Webb Space Telescope (JWST) was initially to be launched in 2007. But delays and technical problems had accumulated, to the point that the project had ended up becoming a kind of Arlesian of observation. celestial.

The costs had also exploded. From an initial estimate of $ 500 million, they finally reached nearly $ 10 billion. A painful for the most part settled by NASA, the main architect of the JWST. But the European Space Agency (ESA) and its Canadian counterpart (CSA) are also closely associated with the project. In particular, Europe has provided several instruments. It will also ensure the launch of the telescope, arrived in mid-October by boat at the Guyanese space center, using an Ariane 5 rocket.

What will this telescope be used for?

Among other things, to observe the past of our universe. In astronomy, looking far is like looking at the past, as light or radiation from deep space can take billions of years to reach us. The study of the formation of the first galaxies, which appeared just after the Big Bang, is thus one of the main missions of the JWST.

But the latter should also make it possible to better understand the formation and evolution of galaxies, to study the birth of stars, and to observe exoplanets – a new field of astronomical observation which, in recent years, has the wind. in the stern.

What are the differences with Hubble?

The two space telescopes do not have much in common, and can moreover be seen as complementary. In orbit around the Earth, Hubble operates primarily in visible light. It is, roughly speaking, a giant astronomical telescope. The instruments of the James-Webb telescope, on the other hand, operate in the infrared, which will allow them to study older objects with unparalleled precision. Light from objects moving away from our solar system are in fact shifting towards red, making their observation with a traditional telescope impossible.

The physiognomy of the two tools is also very different. Starting with the size of the mirror: that of the JSWT is three times larger than that of Hubble. In fact, it is so large (6.5m in diameter) that the engineers had to resort to the technique of segmented mirrors. Without it, he would never have been able to fit into the fairing of a rocket. The JSWT mirror is actually an assembly of 18 mirrors, which will unfold in space to form a sort of giant mirror. It also has a huge sun visor, 22 meters long.

Where will he position himself?

No way, like Hubble which hovers 570 km above our heads, of remaining in Earth orbit. To avoid interference from the Earth’s atmosphere, the JSWT will move away a bit. As soon as it is launched, it will set course for the Lagrange L2 point (more explanations on this site), around which it will be maintained. This imaginary point, where the gravitational fields of the Earth and the Sun cancel each other out, will allow it to remain aligned in the same position with respect to our planet and our star. The journey, of around 1.5 million km, will take him 29 days.

However, this positioning has a drawback: at this distance, it is impossible to send humans to repair the telescope, as was the case for Hubble, which was revealed to be totally myopic at the start. Suffice to say that the scientific community risks holding its breath during the four weeks that its crossing will last and during its commissioning.

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