The James Webb Space Telescope (JWST) launched on December 25, 2021, and began sending scientific images in July 2022. It does not replace Hubble but complements it: Hubble is powerful in visible and ultraviolet light, while Webb is designed for infrared.
Why infrared
The universe is expanding, so light from distant galaxies has its wavelength stretched — redshifted. Visible light emitted by the first galaxies, after more than 13 billion years, has shifted completely into the infrared region by the time it reaches us.
Infrared also penetrates dust clouds much better than visible light, allowing for observations inside star-forming regions.
The heat problem
Infrared instruments must be extremely cold; otherwise, the telescope's own heat will overwhelm the signal. Webb solves this in two ways:
- A five-layer sunshield the size of a tennis court, reducing the temperature from about 85°C on the Sun-facing side to -233°C on the observing side
- An orbit around the L2 Lagrange point, 1.5 million km from Earth, where the Sun, Earth, and Moon are always on the same side
The trade-off: at that distance, there is no possibility of repair as was done with Hubble. Everything had to work correctly the first time — including 344 single points of failure during the deployment process.
Segmented mirror
No rocket could fit a monolithic 6.5 m mirror. Webb uses 18 gold-plated hexagonal segments, folded for launch and then unfolded and aligned in space with nanometer-level precision.
What has been found
- Galaxies formed just 300 million years after the Big Bang, which are brighter and more mature than many models predicted
- Exoplanet atmospheric analysis using transmission spectroscopy, detecting CO₂, water, and methane
- Unprecedentedly detailed images of the "Pillars of Creation" and star-forming regions
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References
- [1]Webb Space Telescope — NASA (2024)
NASA, ESA, CSA — public domain
