After numerous delays, the biggest space telescope ever has blasted off on Christmas Day, and will begin its science mission in mid 2022


25 December 2021

The James Webb Space Telescope sits atop an Ariane 5 rocket on the launchpad in French Guiana on 23 DecemberP PIRON/ESA/CNES/Arianespa​ce
The James Webb Space Telescope (JWST) has finally launched. After a long string of delays and budget overruns, the biggest space telescope ever is on its way to begin unravelling some of the toughest mysteries of the cosmos.
After its launch on an Ariane 5 rocket from French Guiana at 1220 GMT, the spacecraft is heading to a gravitationally stable location called a Lagrange point – in this case, the Lagrange point called L2 – that that orbits the sun about 1.5 million kilometres beyond Earth. This distance from the sun will help ensure that the instruments aboard JWST stay cold, a necessity for them to capture clear images.

The massive telescope was carefully folded to fit inside the rocket it launched on, and during its first week in space it will slowly unfurl. Its huge mirror, made up of 18 gold-plated beryllium hexagons, will unfold, along with the five razor-thin, aluminium-coated layers of a specialised polymer film called Kapton which serve as a shield to block light from the sun, Earth and moon in order to keep the telescope cool. Without this shield, the heat absorbed and re-radiated by the observatory would be enough to ruin its pictures of the universe.
Once the telescope is fully deployed, JWST’s operators will turn on the various electronics and scientific instruments and test them. At the end of January, JWST will reach L2, where operators will continue calibrating its instruments for an additional five months or so, after which – if all goes well – it will begin its science mission.

That mission has four main pillars, encompassing many of the most pressing questions in astronomy. To accomplish these goals, it will observe in infrared frequencies, eschewing the visible and ultraviolet light that the Hubble space telescope includes in its repertoire. Its huge mirror will allow it to see objects that are between 10 and 100 times fainter than what Hubble can spot, and in detail 10 times more precise.
That will enable it to glimpse stars and galaxies located up to 13.6 billion light years away to accomplish the first of the mission’s four pillars: figuring out how the first stars and galaxies formed in the hundreds of millions of years after the big bang. The second pillar is to study the formation and evolution of galaxies over time, from the cosmic chaos of the early universe to the relatively peaceful galaxies we see today.
This is not only important for understanding the history of the universe, but also for determining its large-scale structure. Astronomers will be able to use JWST to probe the dark matter content and movement of distant galaxies, which could help solve the question of how fast the universe is expanding and what its ultimate fate may be.
The third pillar of JWST science is understanding how stars and the planetary systems around them form, allowing us to compare our solar system with the countless others across the universe. Finally, JWST will point towards exoplanets orbiting distant stars to peer through their atmospheres and look for potential signs of alien life. The observing time for the first year of operations has already been allotted, and if all goes well, the spacecraft’s fuel reserves should allow for at least 5.5 years of investigating the cosmos from the first stars to now.
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