The universe was born in light. If modern cosmology is right, for the first forty thousand years or so after the Big Bang the most important component in the young, hot universe was electromagnetic radiation, a situation that continued until the universe had cooled sufficiently for the first hydrogen and helium atoms to form. Temperatures were still high enough at that point for the cosmos to be filled with an opaque, glowing plasma. After a few hundred thousand years, as the universe continued to expand and cool, the first neutral atoms formed and a great darkness began, broken perhaps a billion years later by the appearance of the first stars. These pioneers are thought to have been much more massive than their descendants in today’s night sky, each several hundred times the mass of the Sun. They would have been short-lived, as the enormous temperatures at their cores drove nuclear fusion fast enough to exhaust their reserves of fuel in less than a million years, finally exploding in brilliant supernovae. Extreme conditions during the explosion would have stimulated further nuclear reactions, producing carbon, oxygen and a rich variety of other elements which, scattered throughout a nascent galaxy by the power of the explosion, were incorporated into subsequent generations of stars. Though their lives were brief and their existence solitary, with perhaps just one forming per galaxy, the first stars have a long legacy. The Sun, the Solar System and the Earth, not to mention our bodies and much of what we see around us, probably include material that was produced in the dramatic death of the Milky Way’s first star.
In a few months, for the first time, light from some of those first stars will encounter a device capable of recording it. The James Webb Space Telescope, a $10 billion observatory and plausibly the most complex uncrewed spacecraft ever, was launched on Christmas Day and has now completed the most nerve-wracking and complex stages of its preparation.
Because of the expansion of the universe, stars and galaxies which shone brightly thirteen billion years ago in the range of wavelengths detectable by the human eye are now best seen in the infrared. (Crudely put, the light has been stretched into longer waves.) To make the observatory sensitive to this redshifted light, the hexagonal segments that make up JWST’s primary mirror are coated with a thin layer of gold, which is much better at reflecting infrared than visible light. A telescope’s collecting power is dictated by the size of the primary mirror: astronomers, both amateur and professional, suffer from ‘aperture fever’, an insatiable yearning for bigger and bigger mirrors. JWST has a mirror 6.5 metres across, larger than any telescope on Earth built before the 1990s, but also wider than any rocket can hold. On the launch pad, therefore, much of the telescope structure was folded in on itself, stowed in an extremely expensive and fragile piece of origami.
JWST’s launch vehicle was part of the European Space Agency’s contribution to this international project: the Ariane 5 rocket, which launches from Kourou in French Guiana. (Devil’s Island, the site of the penal colony where Alfred Dreyfus and many others were held in the late 19th and early 20th centuries, is a few miles off the coast.) From ‘Europe’s spaceport’ in South America, rockets are launched east over the Atlantic on a trajectory designed to reduce the risk of debris causing damage should anything go wrong. The first Ariane 5 to take to the skies, in 1996, blew itself up less than a minute after launch, leaving its payload – a set of satellites intended to study the solar wind – to be recovered in pieces from the swamps surrounding the spaceport. Several lumps of mangled metal are on display outside ESA facilities as space-age memento mori.
The walls of Nasa’s mission control in Houston are decorated with the mission patches of prior triumphs. European mission control at Kourou memorialises successful launches with a shelf of champagne corks, interspersed with water bottle caps for failures. The main control room, known as Jupiter, follows the style set by Houston in the Apollo era: experts in headsets sit at consoles facing giant screens showing maps and telemetry. (Staff in a less glamorous and windowless bunker nearer the launch pad keep an eye on the rocket too, but it is telegenic Jupiter that always features in reports.) From there, the team watched the launch early on Christmas morning, and – in the clipped and precise language of French astronautics – broadcast confirmation that the rocket’s performance and the placing of JWST into orbit was ‘nominale’ – just as expected.
The rocket’s final act was to return images of the folded telescope sailing into space above the blue curve of the Earth. The spacecraft glints and sparkles in sunlight, but its infrared-sensitive imagers can only work in the dark, at temperatures below -220°C, to prevent the glow of a warm telescope outshining its celestial targets. The solution is a sunshield the size of a lawn tennis court which, to use the measure that appears on bottles of sun cream, provides a solar protection factor of one million. The sunshield, like the mirror, had to unfold after launch to fit in the Ariane nose cone. Engineers dislike dealing with fabrics which can stretch or snag unpredictably. In Spacesuit: Fashioning Apollo (2011), Nicholas de Monchaux documented the material history of the suits worn by astronauts on the Moon, contrasting the flexible garments produced by Playtex with the rigid and clunky options that aeronautical engineers had envisaged. Most components of JWST could snap and lock into place like Meccano, but the sunshield was different and had caused problems before, tearing during testing in 2018 and causing a significant delay to launch.
That incident was just one of a string of delays and near disasters that afflicted a mission initially intended for launch in 2007. Problems also affected the most famous of JWST’s predecessors, the Hubble Space Telescope, which was found shortly after first light in 1990 to have a deformed mirror. Telescope mirrors are made with incredible precision – you could stretch Hubble’s to the size of the continental United States without finding a bump an inch high – but the lack of a single washer, no more than a millimetre thick, missing from a piece of test equipment, had led Hubble’s team to fashion with exquisite care a mirror of the wrong shape. The result was blurred images no better than those achieved from the ground. But Hubble in low Earth orbit could be reached by astronauts on the Space Shuttle, who were able to install a set of corrective optics. This was not an easy task: it involved fumbling with components not designed for manual repair through thick spacesuit gloves, and some nifty design work to fit the necessary components in the thin barrel of the telescope. (The solution, hit on by a senior Nasa engineer while staying at a German hotel, drew inspiration from an unfolding showerhead.)
In the end, the servicing missions were a success, making possible such images as the Pillars of Creation in the Eagle Nebula, and the Hubble Deep Field, the result of a set of observations carried out over Christmas in 1995, when the telescope was pointing at an apparently empty patch of the northern sky, near the bowl of the Plough asterism in the constellation of Ursa Major. The target field is tiny, but staring at it with Hubble for 140 hours revealed more than three thousand galaxies, among the most distant ever seen. The Deep Field gives us a picture of a time when black holes were growing rapidly, galaxies like the Milky Way were still assembling and star formation was at its peak. The universe has been less exciting ever since.
One of the big projects that will occupy JWST during its first year of observation is a long look at the patches of sky where Hubble has already made this kind of deep image, adding the missing opening pages of the cosmic story to those we can already read. In the COSMOS field, a patch of sky the size of three full moons, the new telescope is expected to find half a million galaxies. JWST’s infrared capability makes it an ideal companion to the older observatory, but no astronauts will be on hand to fix its systems if they fail. Low Earth orbit, where Hubble and the International Space Station fly, is nearby – at a few hundred miles up, space is closer to me in Oxford than Edinburgh is – and from there the Earth fills much of the sky. JWST is headed instead for an orbit around the Sun nearly a million miles away. At this position, near the L2 Lagrange point (as theorised by Joseph-Louis Lagrange in his essay on the three body problem), the gravitational pulls of Earth and Sun are in balance, so a spacecraft will orbit in lockstep with the Earth, allowing JWST to turn its back on us, using its sunshield to block out the Earth and Sun. (The precise orbit chosen means the Moon can be hidden too.)
For most spacecraft, the launch is the riskiest phase of the mission, but for JWST the process of unfolding the mirror, sunshield and optical system while beyond the reach of repair was perilous. In the weeks after Christmas, mission control in Baltimore commanded the telescope, hundreds of thousands of miles away and receding at up to a mile per second, to deploy its solar panels, providing power; to fire its rockets twice to adjust its course; to deploy its antenna so it could talk to Earth; to stretch its diamond-shaped sunshield and tension it to separate its layers; to lift the main mirror away from the spacecraft bus; to swing a radiator out from its storage place; to deploy the secondary mirror responsible for guiding light into the telescope’s cameras; and finally to unfold the primary mirror. In all, there were more than three hundred single points of failure: things that simply had to work for the observatory to function. To the team’s palpable surprise, all went well, and Bill Ochs, the project manager, reported to the conclave in mission control after the secondary mirror was latched into place: ‘We have a telescope.’
There is much still to do. A final rocket burn is needed to place JWST in its final orbit, and it will take another five months for the primary mirror to be collimated, the instruments to be put into commission and the telescope to cool down. Soon afterwards, JWST will peer into the heart of stellar nurseries in the Milky Way and its neighbouring galaxies. It will help us understand the ultimate fate of stars like the Sun, destined not for a supernova but for long senescence as a white dwarf. JWST includes a coronagraph that can block out starlight, creating an artificial eclipse, which should reveal any alien Jupiters that exist around nearby stars. Planets beyond the solar system – exoplanets – will be important targets for JWST, as it will measure the presence of carbon dioxide, water and oxygen in the atmospheres of planets orbiting nearby red dwarf stars, probing the suitability of those systems for life. Such observations need fair weather – clouds in the atmospheres of the target worlds will scupper even a space telescope’s attempts at observational astronomy – but they are immensely exciting, with targets including putative planets around Proxima Centauri, the nearest star to the Sun, and Tau Ceti, the home system of the double planets Anarres and Urras in Ursula Le Guin’s The Dispossessed.
When work started in earnest on what was then called the Next Generation Space Telescope in 1996, the first planets around normal stars had only just been identified; the JWST will spend about a third of its time chasing the new worlds that have been discovered since. Much of what the telescope will do over the next two decades – a lifetime doubled by the fuel-saving precision of the launch from Kourou – is still to be determined, but among its most important results will be the first image of light emitted by the universe’s first stars and galaxies, collected by a fragile golden mirror that now sits, unfurled, in the remoteness of space, waiting in the dark to report secrets nearly 14 billion years old to Earth’s astronomers. Telescopes are time machines, bringing ancient light from the universe’s past to be observed in the present, and JWST is our most powerful yet.
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