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TEXTThe James Webb Space Telescope
The James Webb Space Telescope: Seeing the Light of the First Galaxies
The James Webb Space Telescope (JWST) is the largest observatory ever sent into space. It is a partnership between NASA, the European Space Agency (ESA), and the Canadian Space Agency (ASC). It launched on December 25, 2021, aboard an Ariane 5 rocket from the Guiana Space Centre in Kourou. Its total cost is estimated at nearly $10 billion.
Why Observe in the Infrared?
The light from the most distant galaxies has traveled for over 13 billion years. With the expansion of the Universe, its wavelength has stretched: light emitted in the visible spectrum reaches us today in the infrared. Infrared light also pierces through the dust clouds that conceal the birth of stars and planetary systems. Webb observes between 0.6 and 28.5 micrometers, ranging from visible red to mid-infrared.
A Giant, Foldable Mirror
The primary mirror measures 6.5 m in diameter, compared to 2.4 m for Hubble. It consists of 18 hexagonal beryllium segments coated with a thin layer of gold, which reflects infrared light exceptionally well. Its collecting area reaches approximately 25 m², more than five times that of Hubble (about 4.5 m²). Too large to fit inside the rocket's fairing, the mirror was folded like origami and then unfolded in space.
A Shield Against the Sun
To detect faint heat from vast distances, the telescope itself must remain extremely cold. A five-layer Kapton sunshield, about the size of a tennis court (roughly 21 m by 14 m), protects the instruments from the light of the Sun, Earth, and the Moon. On the shaded side, the temperature drops below 50 kelvins, around −223 °C. The MIRI instrument is cooled even further, down to about 7 kelvins, using a cryocooler.
Far From Earth, at the L2 Point
Hubble orbits the Earth at an altitude of about 540 km. Webb, on the other hand, orbits the Lagrange point L2, roughly 1.5 million km from Earth on the side opposite the Sun. At this location, the Sun, Earth, and Moon always stay on the same side, behind the sunshield. However, unlike Hubble, no astronaut servicing missions are planned.
A High-Risk Deployment
After launch, the telescope had to deploy autonomously over several weeks: opening the sunshield, tensioning its five layers, and deploying the secondary mirror, followed by the two wings of the primary mirror. Engineers identified 344 single points of failure—critical steps where failure would compromise the entire mission. Webb reached its orbit around L2 on January 24, 2022. It then took several months to cool the instruments and align the 18 segments to function as a single mirror.
Four Scientific Instruments
- NIRCam, the near-infrared camera, which captures the bulk of the images.
- NIRSpec, a spectrograph capable of analyzing light from dozens of objects simultaneously.
- MIRI, the mid-infrared instrument, serving as both a camera and a spectrograph.
- NIRISS, paired with the FGS guidance sensor, which maintains the telescope's ultra-precise pointing.
First Images and Discoveries
The first full-color images were released on July 12, 2022, including the deep field of galaxy cluster SMACS 0723, the Carina and Southern Ring Nebulae, and Stephan's Quintet. Since then, Webb has identified galaxies that existed just a few hundred million years after the Big Bang, and it analyzes the atmospheres of exoplanets—detecting, for instance, carbon dioxide around exoplanet WASP-39 b.
Hubble and Webb: Two Complementary Telescopes
Hubble, launched in 1990, observes primarily in the ultraviolet and visible spectra, with some near-infrared capabilities. Webb is optimized for the infrared. Astronomers frequently combine data from both: Hubble reveals stars and hot gas, while Webb uncovers dust, forming stars, and the most distant objects.
Unexpected Longevity
The mission was designed for a minimum of five years, with a goal of ten. Thanks to the launch's precision, the telescope conserved fuel, and NASA estimates it has enough propellant for well over ten years of science operations.
Sources: NASA, "James Webb Space Telescope" (science.nasa.gov/mission/webb) and European Space Agency (esa.int, Webb section).
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The James Webb Space Telescope: Seeing the Light of the First Galaxies
The James Webb Space Telescope (JWST) is the largest observatory ever sent into space. It is a partnership between NASA, the European Space Agency (ESA), and the Canadian Space Agency (ASC). It launched on December 25, 2021, aboard an Ariane 5 rocket from the Guiana Space Centre in Kourou. Its total cost is estimated at nearly $10 billion.
Why Observe in the Infrared?
The light from the most distant galaxies has traveled for over 13 billion years. With the expansion of the Universe, its wavelength has stretched: light emitted in the visible spectrum reaches us today in the infrared. Infrared light also pierces through the dust clouds that conceal the birth of stars and planetary systems. Webb observes between 0.6 and 28.5 micrometers, ranging from visible red to mid-infrared.
A Giant, Foldable Mirror
The primary mirror measures 6.5 m in diameter, compared to 2.4 m for Hubble. It consists of 18 hexagonal beryllium segments coated with a thin layer of gold, which reflects infrared light exceptionally well. Its collecting area reaches approximately 25 m², more than five times that of Hubble (about 4.5 m²). Too large to fit inside the rocket's fairing, the mirror was folded like origami and then unfolded in space.
A Shield Against the Sun
To detect faint heat from vast distances, the telescope itself must remain extremely cold. A five-layer Kapton sunshield, about the size of a tennis court (roughly 21 m by 14 m), protects the instruments from the light of the Sun, Earth, and the Moon. On the shaded side, the temperature drops below 50 kelvins, around −223 °C. The MIRI instrument is cooled even further, down to about 7 kelvins, using a cryocooler.
Far From Earth, at the L2 Point
Hubble orbits the Earth at an altitude of about 540 km. Webb, on the other hand, orbits the Lagrange point L2, roughly 1.5 million km from Earth on the side opposite the Sun. At this location, the Sun, Earth, and Moon always stay on the same side, behind the sunshield. However, unlike Hubble, no astronaut servicing missions are planned.
A High-Risk Deployment
After launch, the telescope had to deploy autonomously over several weeks: opening the sunshield, tensioning its five layers, and deploying the secondary mirror, followed by the two wings of the primary mirror. Engineers identified 344 single points of failure—critical steps where failure would compromise the entire mission. Webb reached its orbit around L2 on January 24, 2022. It then took several months to cool the instruments and align the 18 segments to function as a single mirror.
Four Scientific Instruments
- NIRCam, the near-infrared camera, which captures the bulk of the images.
- NIRSpec, a spectrograph capable of analyzing light from dozens of objects simultaneously.
- MIRI, the mid-infrared instrument, serving as both a camera and a spectrograph.
- NIRISS, paired with the FGS guidance sensor, which maintains the telescope's ultra-precise pointing.
First Images and Discoveries
The first full-color images were released on July 12, 2022, including the deep field of galaxy cluster SMACS 0723, the Carina and Southern Ring Nebulae, and Stephan's Quintet. Since then, Webb has identified galaxies that existed just a few hundred million years after the Big Bang, and it analyzes the atmospheres of exoplanets—detecting, for instance, carbon dioxide around exoplanet WASP-39 b.
Hubble and Webb: Two Complementary Telescopes
Hubble, launched in 1990, observes primarily in the ultraviolet and visible spectra, with some near-infrared capabilities. Webb is optimized for the infrared. Astronomers frequently combine data from both: Hubble reveals stars and hot gas, while Webb uncovers dust, forming stars, and the most distant objects.
Unexpected Longevity
The mission was designed for a minimum of five years, with a goal of ten. Thanks to the launch's precision, the telescope conserved fuel, and NASA estimates it has enough propellant for well over ten years of science operations.
Sources: NASA, "James Webb Space Telescope" (science.nasa.gov/mission/webb) and European Space Agency (esa.int, Webb section).