why the James Webb telescope will revolutionize space observation by succeeding Hubble

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Astronomers have been talking about it for twenty years. After multiple postponements and delays, the James Webb telescope must be launched this Saturday, December 25, thanks to an Ariane 5 rocket. Franceinfo explains why this new telescope, the cost of which has exploded to reach 10 billion dollars (8, 9 billion euros) – funded by NASA, the European Space Agency and the Canadian Space Agency – will revolutionize space observation, whether to scan objects relatively close or very distant.

Because it’s the most powerful telescope ever to go into space

The James Webb space telescope (JWST), also simply referred to as the James Webb, is considered like a gem of space engineering. It is equipped with a large mirror made up of 18 small hexagonal mirrors. Once in space, the whole must unfold like an origami, as shown in this video (in English).

When deployed, the JWST is 8 meters tall, and its sunshade, which is five layers thick, spans an area the size of a tennis court. “Normally, mechanisms like those present on the JWST are the haunt of space engineers. ” by that they fear that they will block or that they open badly, remark to franceinfo Olivier Berné, astrophysicist at the CNRS. “There are a hundred of them. It is unprecedented and it is already an extraordinary mission from this point of view “, comments the one who is also responsible for a scientific project on the James Webb.

Above all, the JWST, which weighs 6 tons, is the most powerful telescope ever to be sent into space. To come back to the mirror, which measures the power of a telescope, that of Hubble, launched in 1997, is 2.4 meters wide while that of the JWST is 6.5, as explained in this video from NASA (in English).

Concretely, since James Webb’s mirror is larger than Hubble’s, it can capture more light and therefore see much further. What also to have a better resolution.

“It’s a gap technology which is achieved with the James Webb, thanks to instruments never built before. “

Anthony Boccaletti, astronomer at the Meudon Observatory

to franceinfo

Unlike its cousins ​​on Earth, the JWST will not be hampered by the light and atmosphere of our planet: it will be placed 1.5 million kilometers from us, at the second point of Lagrange (while Hubble is in orbit at 570 km above our heads).

Because it will allow us to see the universe in an unprecedented way

“One of the scientific goals of JWST is to look at the light of the first stars that formed soon after the big bang, explains Olivier Berné. We do not really know how these first stars were created, necessary for the enrichment of the universe in heavier chemical elements “, he continues.

However, in order to be able to look at such ancient and distant objects, you have to place yourself in the infrared. Indeed, the universe is expanding, the planets, the galaxies are constantly moving away from us. With this distance, the light of these celestial objects shifts towards the red, a phenomenon called “Doppler effect” in French (“red shift “ in English).

Designed to work in the infrared, the JWST will thus be able to probe the universe very deeply and observe for the first time very old objects formed 13.5 billion years ago (compared to 12.5 billion years for Hubble ). In other words, we will be able to observe the universe when it was very young since the big bang took place about 13.7 billion years ago. Michel Blanc, astronomer emeritus at the Institute for Research in Astrophysics and Planetology, evokes a “formidable breakthrough”.

“If Hubble has kept observation in visible light and ultraviolet very well, James Webb works mainly in the infrared. He opens new doors.”

Michel Blanc, astronomer

to franceinfo

To better understand the contribution of infrared, here is an example of what it allows compared to visible light. In these two photos taken by Hubble and shared via James Webb’s official Twitter account, the image on the left is in visible light. The one on the right, in infrared light. We notice that, on the second, the visible objects are much more numerous and that the infrared makes it possible to see through the dust.

And here’s a simulation of what James Webb might be able to do. The image on the left shows visible light, the image on the right gives an idea of ​​what the JWST might produce.

Working specifically in the infrared is nothing new. The Spitzer telescope is specialized in this field. But the James Webb is 1,000 times more powerful than the latter, according to NASA (in English).

Such detailed observations will have multiple repercussions. If he is cautious about the content of the discoveries to come, Anthony Boccaletti, astronomer at the Observatory of Meudon (Hauts-de-Seine), told franceinfo to be “certain” that the JWST will be the source of significant advances in our knowledge.

“There are going to be major breakthroughs in many areas of astrophysics thanks to the JWST.”

Anthony Boccaletti

to franceinfo

Because it will make it possible to rediscover already known celestial objects

His ability to work in the infrared also allows James Webb to observe cold bodies, which are more difficult to detect. This is what Thierry Fouchet, from the Laboratory for Space Studies and Instrumentation in Astrophysics in Paris, will show.

He is working on a project illustrating the capabilities of JWST. He will not point it in the direction of a distant object, but will focus on those relatively close to us and cold: Jupiter, its rings and its moons. By pushing the tools of James Webb to its limits, he will, among other things, study the satellites of the largest planet in our solar system, such as Io, Ganymede and Callisto. Its objective: to map the ice sheets that are on their surface, to establish their age, their temperature, and the speed at which they recompose.

For the study of Jupiter, he admits that he does not expect any astonishing novelties. “We will be more in the refinement” of our current knowledge, he concedes. The discoveries are rather expected for the satellites.

“I wouldn’t be surprised if we were surprised. We have very little information. It’s not clear what to expect and nothing has yet been robustly verified.”

Thierry Fouchet, astrophysicist at the Paris Observatory

to franceinfo

Because it will help us to better understand exoplanets

Since the discovery of the first planet outside our solar system in 1995, new finds have been raining down. Except that these often very distant stars are still unknown. “The JWST will allow them to be observed with unparalleled precision”, comments Olivier Berné, astrophysicist at the CNRS and in charge of the scientific project on the telescope.

“We’re going to be able to look inside planetary systems as if we were looking at our own. This is something particularly new.”

Olivier Berné, astrophysicist

to franceinfo

Astrophysicists will obtain precise information on the composition of the atmospheres of exoplanets, such as temperature and density. They will also have data on the presence or absence of “organic molecules which can be precursors of life”, notes the astrophysicist.

Targeted exoplanets “are very young, very big and very hot. So they cannot shelter life nor be habitable”, tempers Anthony Boccaletti. “Discovering a habitable exoplanet and telling yourself that there is life elsewhere in the universe is the ultimate goal, but it is not the majority of the observations that we will make with James Webb”, he adds.

Because it opens the way to the observation of very little studied phenomena

Nicole Nesvadba, astrophysicist at the Côte d’Azur Observatory, is interested in supermassive black holes, which are found at the center of galaxies and form between a million and several billion solar masses. If the first direct image of a supermassive black hole was published in 2019, “we don’t know much about these quite exceptional phenomena“, she explains to franceinfo.

Here is the first image of a black hole ever presented. It was produced as part of the international EHT project and unveiled on Wednesday April 10, 2019. (EHT COLLABORATION)

According to her, the JWST will most likely be “revolutionary” to understand how supermassive black holes interact with their environment. It will allow to observe “in detail” a phenomenon that has not been studied “seriously” that once thanks to the Spitzer telescope, about ten years ago, she explains.

With the JWST, researchers will in particular be able to examine the “galactic winds” generated by the supermassive black hole of the galaxy 3C326N, which is about 1 billion light years from Earth. In line of sight: gases which cannot be observed from the ground. Their behavior could shed light on why this galaxy hasn’t formed stars for ten billion years.


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