Fourth anniversaries usually aren’t reasons for celebration. However, in the case of the James Webb Space Telescope (JWST), which launched on December 25, 2021, this anniversary represents an important transition.
Up until now, JWST has been in discovery mode. It took a generation to develop and cost a significant amount. It is the most powerful telescope in history, capable of observing at distances and with levels of detail never seen before.
But like any major new scientific instrument, astronomers had to see JWST in operation before they could answer the fundamental question that will drive research for decades to come: How much of our universe can we observe?
JWST builds upon the progress the Hubble Space Telescope has made since its launch in 1990. The Hubble mainly observes space through the visible part of the light spectrum – the part our eyes have evolved to perceive. JWST, on the other hand, primarily sees in the infrared, enabling it to penetrate cosmic dust, observe cooler objects, and look into the early universe.
Since the speed of light is finite, observing objects at greater distances means looking further back in time. And because the expansion of the universe – the expansion of space itself – has stretched the visible light from the most distant objects into the infrared, JWST can search for the first sources of light, approximately 100 million years after the Big Bang.
Four frontiers
Edwin Hubble, the American astronomer after whom the Hubble Space Telescope is named, stated in 1936 that “The history of astronomy is a history of receding horizons.” NASA, with the assistance of the European Space Agency and the Canadian Space Agency, has identified four such horizons, frontiers that they designed JWST to cross.
The first is the frontier that Galileo crossed in the early 17th century when he pointed a primitive perspective tube (what we would call a telescope) at the night sky and bridged the ancient, previously unbridgeable gap between the terrestrial and the celestial. By discovering evidence that the Earth orbits the Sun rather than the other way around, Galileo implicitly redefined the Earth as just one more member of a system of planets.
Now, thanks to JWST, the deep history of the solar system is coming into clearer view. By studying the surface chemistry of numerous icy objects far beyond Neptune, the most distant planet, JWST researchers can trace the emergence and evolution of the entire solar system. Meanwhile, the discovery of water among asteroids – a belt of “debris” between the orbits of Jupiter and Mars – raises the possibility that comets weren’t the only objects providing the ingredients for life in Earth’s primordial atmosphere.
But our Sun is just one star. Beyond the solar system’s horizon lie the hundreds of billions of other stars in our Milky Way galaxy, many of them having planetary systems. Astronomers are using JWST to study systems in various stages of development – from primitive “protostars” that are just starting to gather the gas and dust that will eventually form a disk of orbiting objects, to fully mature planetary systems like our own. Or unlike our own.
JWST has discovered, in one planetary system after another, a type of planet that is different from those in our system. Our system has traditionally been divided into two categories: gas giants (Jupiter, Saturn, Uranus, Neptune) and small rocky planets (Mercury, Venus, Earth, Mars). But thanks to JWST, we now know that other planetary systems include variants that astronomers call a mini-Neptune (gas surrounding a rocky core) or a super-Earth (perhaps a former mini-Neptune that has lost its atmosphere).
But our Milky Way is just one galaxy. Beyond that horizon – as Hubble the astronomer himself discovered in the 1920s – there are other galaxies. Similar to the planetary systems in the Milky Way, astronomers are also using JWST to study galaxies across the universe that are in various stages of development, from clouds of gas, to collisions of clouds of gas, to star births, to star deaths. Some of those deaths – exploding stars, or supernovae – might help explain a problem that has puzzled astronomers for half a century: The universe seems to have more dust than astronomers can account for, yet that dust must be coming from somewhere. Could that source be supernovae? Preliminary studies have been promising.
Supernovae themselves offer another clue to the universe’s evolution. Scientists have known since the 1950s that successive generations of supernovae, due to thermonuclear forces breaking apart and rearranging the basic building blocks of matter, create heavier and heavier elements. Since its inception, JWST’s ultimate goal has been to find the first, “pristine,” galaxies, containing only hydrogen and helium. To do so, JWST would have to cross the horizon that the visible-light Hubble Space Telescope itself couldn’t reach: a cut-off around one billion years after the Big Bang.
So far, JWST has been able to observe galaxies, supernovae, and black holes as far back as 300 million years after the Big Bang. Although that might seem like a long time, it’s just a short period in a universe that’s 13.7 billion years old.
And JWST researchers are just beginning. They expect the JWST project to continue well into the 2040s. That means there will be many more anniversaries. We should hope they’ll all be as worthy of celebration as this one.
