James Webb : 13 questions pour comprendre la mission du télescope spatial

James Webb : 13 questions pour comprendre la mission du télescope spatial

The James Webb Space Telescope (JWST) is located 1.5 million kilometers from Earth. In mid-July 2022, the first official photos of the observatory were published. The result is fabulous. Hubble’s succession is assured.

James Webb has finally shown what he’s capable of. The space telescope, which is now 1.5 million kilometers from Earth, obtained the first historical photo of the bottom of the Universe, released on July 11, 2022. The event was so historic that even Joe Biden, the president of the United States, participated in the parties. Even in France, Emmanuel Macron went there with his tweet.

Then, on July 12, the observatory further delighted astronomers, the public, and journalists with snapshots showing the remains of a dying star, a cosmic ballet between four galaxies, the secrets of a giant exoplanet, and what they’re like. cosmic cliffs, where stars are born. , in vast nebulae. These shots of James Webb are dizzying.

The capabilities of the telescope, developed by the US Space Agency with the help of its European and Canadian counterparts, are colossal. Just make a simple comparison between James Webb and Hubble. Or to see how the area imaged by the observatory is only a small fraction of the entire Universe. And yet, the details are incredibly precise.

Here you will find everything you need to know about the exciting JWST mission, which will provide astronomers around the world with spectacular observations from space.

What about the James Webb telescope?

It’s done: the James Webb Telescope is in space! The launch was successful on December 25, 2021. Then it remained to be fully operational. In total, more than 300 critical points have been identified as potentially problematic during its deployment; obviously, they were closely examined by NASA.

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What is the James Webb Telescope used for?

This observatory was designed to advance research in four main areas:

  • Detect the light of the first galaxiesthat appeared shortly after the Big Bang,
  • For study the formation and evolution of galaxies,
  • Better understanding the birth of stars,
  • As much as exoplanets.

To do this, the JWST observes in the infrared range (that is, the radiation between visible light and microwaves) and in space. Thus, the observatory is able to go back into the past of the Universe, see the first galaxies in formation – “baby galaxies” – and inspect the interior of the dust clouds in which stars and planets are formed.

What are the instruments of the James Webb Telescope?

The observatory has four scientific instruments on board:

  • A near infrared camerathe NIRCam (for “Near Infrared Camera”), which will, among other things, detect stars that appeared after the Big Bang, search for supernovae, measure distorted light due to dark matter,
  • A near infrared spectrometerthe NIRSpec (“Near-Infrared Spectrometer”), which allows, for example, to study the chemical elements in distant galaxies or clusters of young stars,
  • A mid infrared instrumentthe MIRI (“Mid Infrared Instrument”), with which it is possible to observe in particular brown dwarfs, exoplanets and the evolution of stars and protoplanetary systems,
  • And a near-infrared imager and slitless spectrographsays NIRISS (“Near Infrared Imager and Slitless Spectrograph”), which helps study exoplanets and distant galaxies.

Why does the James Webb telescope have a segmented mirror?

The sumptuous primary mirror of the James Webb telescope, with an estimated diameter of 6.5 meters, does not go unnoticed with its golden coloration and its 18 segments assembled in a hexagonal shape. In astronomy, the mirror is said to be segmented. It is not a technical choice, because it would have been possible to build it in a single block.

There is a logistical motivation behind this choice: it would have been impossible to fit a mirror of this size made up of a single block on the rocket that launched the JWST into space. Therefore, for the first time, it was decided to launch a telescope with a segmented mirror into space.

Will the James Webb Telescope replace Hubble?

It would not be entirely accurate to say that the James Webb Space Telescope is intended to replace Hubble. You have to see it more as a successor. It is true that JWST exceeds a limit of Hubble, which turns out to be unable to see beyond the near-infrared (thus going back less than JWST). It is also larger than Hubble in size.

But the day Hubble is no longer working, the James Webb Telescope will not have the means to completely replace it. Hubble is currently the only telescope capable of observing in the ultraviolet, and JWST is not equipped to do the same.

When was the James Webb telescope launched?

The launch of the James Webb Space Telescope was originally scheduled for December 18, 2021. Finally, its launch took place on Christmas Day, December 25, 2021.

Where was the James Webb telescope launched from?

It took off from the Kourou space center in French Guiana, transported aboard an Ariane 5 ECA rocket. The observatory had to be transported by ship from California to reach its launch site.

How much does the James Webb telescope cost?

The total cost of the telescope is estimated at 9.7 billion dollars, or 8.2 billion euros. Since the beginning of the project, this budget has been periodically revised upwards.

NASA mentions that it participates in the total cost of the JWST in the amount of 7,998 million dollars. She estimates that the first five years of operation of the observatory, added to the two years necessary for the exploitation of its data, will generate an additional cost of 8,835 million dollars, knowing that the JWST will certainly have to double its useful life.

Why was the launch of the James Webb Telescope postponed?

The JWST flight into space has been repeatedly postponed. In 2003, the planned date for its departure to space was 2011. However, that year the calendar had to be readjusted due to regular problems and the budget increase. US congressional representatives have even considered canceling the project, which has become too costly. However, the release was delayed until 2018.

And since then, takeoff has been continually postponed. The covid-19 pandemic has further disrupted the pace of work, forcing the launch date into space to be further postponed to the end of 2021.

Why is the name of the James Webb Telescope controversial?

At the beginning of the project, the telescope received the temporary designation “Next Generation Space Telescope” (NGST, for “Next Generation Space Telescope”). It was so named to symbolize the continuity of its activities, compared to those of Hubble.

The JWST received its official name on September 10, 2002, in reference to James Webb (1906-1992), NASA’s second administrator. He is known for leading Apollo. However, this choice of name is questioned by many scientists, since James Webb would have favored a policy of exclusion of LGBTQI+ people within the space agency. However, NASA does not intend to change the name.

Why is it necessary to send the James Webb telescope into space?

It was necessary to make the JWST a space telescope, and not a terrestrial one, because this observatory requires very specific observation conditions. The Earth’s atmosphere could cloud the images obtained by the telescope, because it is almost opaque and shines in the infrared wavelengths that James Webb will observe. Currently, the technologies used in ground-based telescopes do not allow to circumvent this problem.

This need to send it into space makes the mission even more complex: all the mechanisms of the JWST must work perfectly.

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The JWST, in the stowed position.  // Source: Northrop Grumman via Flickr (cropped photo)

Where is the James Webb Telescope placed in space?

It took about a month for the telescope, after its launch, to reach its intended location: the Lagrange point L2, located about 1.5 million kilometers from our planet. It is essential to place the JWST very far away, since it needs a low temperature to work properly (-223°C). Its 5-layer shield helps keep it cool by blocking light emitted by the Sun, Earth, and Moon (it could, by heating the telescope, distort your observations).

But in addition to the shield, the position of the space telescope plays a role: it is positioned behind the Earth, relative to the Sun. Therefore, the JWST is approximately aligned at all times with our planet and the Sun.

At that distance, repairs in space, such as the maintenance missions carried out with Hubble, are not foreseen.

How long should the James Webb Telescope mission last?

Since its launch, the telescope has been designed so that its mission lasts at least 5.5 years (including the first six months of commissioning). Rather, the goal would be for its useful life to exceed 10 years. Unlike the Hubble telescope, it is not so much the functioning of its various components that is likely to become problematic over time. Rather it is the amount of fuel embarked by the observatory to maintain its orbit that will be decisive. Therefore, the JWST carries enough fuel to be operational for about ten years.

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Final primary mirror wing folding tests.  // Source: Northrop Grumman via Flickr (cropped photo)

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