Science

James Webb Telescope Launch: “We look forward to learning about the childhood of the first stars”

The James Webb Space Telescope (JWST), the most anticipated scientific instrument since the early 21st century, will finally take off. The launch, initially scheduled for December 18, has been postponed to December 22, then to December 24 and finally to December 25 … But this time (it should) be the right one. Installed in the fairing of an Ariane 5 rocket, the telescope will launch from the Kourou Space Center in French Guiana to begin a six-month journey to its destination, Lagrange point 2, which is located 1.5 million miles away. kilometers, almost four times farther than the distance that separates us from the Moon.

There he will begin a mission that will last at least five and a half years. It promises to revolutionize our understanding of the history of the universe. A turning point for the US Space Agency (NASA), but also for its European and Canadian partners. Pierre Ferruit, scientific director of the telescope of the European Space Agency (ESA) interviewed by L’Express, describes the objective of this space telescope and tells us his expectations and hopes.

L’Express: It took thirty years of development and almost $ 9.7 billion in investment … The initial launch was scheduled for 2007! Even recently, it has been rejected three times. What is the current voltage level?

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Pierre Ferruit: The pressure and excitement are mounting: we’ve been waiting for this moment for so long! I have been working on this project since 1999 (22 years!), Which represents the majority of my scientific career. There will likely be a bit of tension as well, because all pitches are risky. But the JWST is in good hands, it will depart aboard an Ariane 5 rocket, one of the most reliable launchers in the world. It is reconfortable. There is also pride, because JWST is as exceptional as it is unique, its mission fascinates people and will contribute a lot scientifically.

The telescope’s deployment, currently dubbed as a giant origami on the rocket’s fairing, promises to be the most complex in the history of space exploration. NASA evoked 344 possible “points of failure,” including 144 mechanisms that must fit together perfectly. It’s new.

It is the most complex scientific mission ever launched involving thousands of researchers. And this scientific ambition goes hand in hand with building something technically extraordinary. Due to its size, JWST must be folded up before launching. Most of the mechanisms he talks about are a consequence of the fact that he has to unfold in space. It will take us about four weeks, because we will do it very carefully.

Especially since it will not be possible to go to repair it if there is a problem. [le point Lagrange 2 est trop éloigné de la Terre, NDLR]. Therefore, it was necessary to make sure before that everything was going to work well: think about the robustness of the telescope, have multiple systems in case of failure, multiply the tests as NASA did until the last hours before launch. Field teams have even been trained to deal with potential problems! But all this groundwork indicates that we are ready.

Europe is a partner with the United States in this mission, but to what extent will it benefit from these discoveries?

In exchange for our contributions – providing a team of fifteen people, but also the Ariane 5 launcher and two of the four instruments – we are entitled to a minimum of 15% of the observation time. We even improved a bit. We will use this time to observe the galaxies and the supermassive black hole they host at their center, in order to better understand the relationship between the two. We will also examine areas where stars form, or even auscultate exoplanets. [des planètes qui ne se trouvent pas dans notre système Solaire, NDLR]. This will be distributed to approximately one third for each project.

The special thing about JWST is that it is seen in the infrared spectrum, why is this so important?

In the 1990s, thanks to the Hubble Space Telescope, we began to better understand the evolution of galaxies. But in our quest to look beyond, therefore, to go further back in the history of the universe, we have run into the limits of Hubble. Because to observe objects far away from us, we needed a bigger mirror and therefore a bigger telescope. For the JWST, its pupil is its main mirror, the size of which allows it to collect more light.

The second thing is that the further the light is, the more it shifts towards the red, all the way to the infrared. So if we want to look inside the universe and therefore go very far back in time, we need an infrared observatory. Infrared vision is essential for observing the galaxies that were born first in the history of the universe. It also allows us to see the star nurseries better, because the infrared passes through the clouds of dust and gas that are very present in these areas.

This technology will also allow us to better study exoplanets that we did not know existed when JWST was designed. Infrared will help us learn more about the composition of your atmosphere and will be able to detect possible chemical signatures of water, methane, etc., what we call biological signatures, that is, indicate the ingredients that can give life. In our quest to find out whether or not we are alone, we know that life as we know it needs liquid water, so logically we will try to find out if there are any on the exoplanets we will observe. It will not show that there is life elsewhere, but it will be a first step.

Ground-based telescopes, like the VLT in Chile’s Atacama desert, can also look into the infrared spectrum and see objects more than 11 billion light-years away. Why launch a telescope into space?

It’s true, ground-based telescopes have infrared vision. But Earth’s atmosphere contaminates these observations, because water molecules in our atmosphere absorb some of the infrared light, so some of the information is missing. James Webb will have a sensitivity 10 to 100 times greater than any existing instrument. Thus, it will detect less luminous objects, but it will also be able to go very far back in time, seeing objects located 13.5 billion light-years away. We are already approaching 13 billion years, but we have not necessarily been able to observe these objects accurately. But, like humans, knowing what happened in the infancy of the first stars or galaxies explains what they are today. This will allow us to better understand the evolution of the universe.

How do the four instruments on board the telescope work?

There are three instruments that will look at space in the near infrared spectrum and one in the mid infrared. The NIRCam (Near Infrared Camera) was provided by the University of Arizona (USA). It is the main instrument for near infrared imaging. It is also equipped with a coronagraph, which allows starlight to be masked when observing exoplanets, allowing us to see relatively young gas giants.

The NIRISS imager (Near Infrared Imager and Slitless Spectrograph) manufactured in Canada will act as a support for NIRCam. It will also perform spectroscopy, which captures the image of an object and breaks it down into different shades in order to detect signatures that inform us in particular about its physical and chemical composition. It has a dedicated mode for observing exoplanets and another for galaxies.

The NIRSpec (Near Infrared Spectrometer) spectrometer developed by ESA is a pure spectrograph. It will allow you to observe between 50 and 200 objects at a time, which is particularly important since when we observe very distant objects, hours, even days of observation are required. But Webb’s time is precious.

The fourth instrument, MIRI (Mid InfraRed Instrument), is American-European. It allows you to see even more in red than the others – it is the only one that will search in the mid-infrared. It is a Swiss Army knife, because it is an imager, a spectroscope, and a coronagraph.

James Webb will also be equipped with a heat shield, which will cool your equipment, why?

Because heat emits infrared. Detection of a human body in the dark is possible, for example, with infrared glasses. If James Webb does not cool down, his own heat could alter his observations. Just like if you want to look at the sky at night, you shouldn’t stand under a streetlight. The heat shield will allow it to cool to -230 ° C, while on the side exposed to the sun, it will heat to + 80 ° C. Our Miri instrument will even have a cryocooler, built by the United States, an active device that will keep it at – 266 ° C.

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Once the launch into orbit is successful and the JSWT is officially handed over to scientists, when do you expect to get the first results?

The first scientific communications will take place from June, the official start date of the scientific program. This has already been established for the period June 2022 to June 2023. But depending on the findings, the schedule that will follow may change: as for all ground-based observatories, new calls for tenders will be opened for the JWST each year. Research teams may apply proposing new scientific projects. Science adapts but thus advances, in small steps. And for durations that seem to defy understanding. In hindsight, what is interesting to note is that since the Hubble epic, all unanswered questions fully validate the James Webb telescope. Hence this exceptional investment. Trust me, the game is worth the effort.

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