There is a distant world where quartz crystals float above a red-hot, puffy atmosphere. Evaporated grains of sand, not water droplets, form the clouds that fill the sky on Wasp-107b, a planet 1,300 light-years from Earth.
Then there is GJ1214, the sauna planet. With a mass eight times that of Earth, it orbits its parent star at a distance one-seventieth the distance between Earth and the Sun, and appears to be covered in a thick, dense atmosphere that contains enormous amounts of steam.
Or there are the gigantic, Jupiter-sized planets of the Orion Nebula discovered floating free in space, rogue worlds that appear to have no connection to any parent star – to the bafflement of astronomers.
These strange, remote planets couldn’t be more diverse or dramatically different from each other, though they share one common feature. Their wonders are now being revealed by the James Webb Space Telescope (JWST).
Launched on Christmas Day 2021, the $10 billion robotic observatory is currently transforming our understanding of the planets in our Milky Way. “It took six months to position the telescope and get the systems working properly – meaning 2023 was the first full calendar year of operation,” said astrophysicist Dr Hannah Wakeford from the University of Bristol. “The results have exceeded all our expectations.”
The JWST consists of a gold-plated mirror of 6.5 meters; a sunshade the size of a tennis court; and a series of complex instruments cooled to temperatures just a few degrees above absolute zero. These features allow the telescope to observe the sky in infrared radiation, revealing details of the universe just after the birth of the Big Bang 13.8 billion years ago, and images of stars being born in dust clouds.
However, the JWST gives science an extra gift: infrared radiation also turns out to be ideal for studying extrasolar planets, or exoplanets, as worlds orbiting other stars are known. The telescope thus unleashes an astronomical revolution.
For centuries, the only planets known to man were the few we could see in our solar system. But was the Sun’s family typical, scientists wondered? Were planets plentiful or rare elsewhere in the Milky Way? These questions were crucial because the last scenario – a cosmic scarcity of planets – would mean that extraterrestrial life would probably also be scarce.
The problem for astronomers was the simple fact that stars are very bright, but planets are much smaller and much fainter, and could not be detected next to their brilliant celestial parents. It was not until the end of the last century that a new generation of highly sensitive cameras, mounted on telescopes and orbiting observatories, could detect the slight dimmings of exoplanets as they passed in front of stars.
After the first few of these transit observations were made, discoveries began to multiply dramatically. Today, the total number of observed exoplanets stands at 5,566, according to NASA’s Extrasolar Planet Archive.
Crucially, several hundred are relatively close to Earth and these are now ripe for study by the JWST, astronomers say. Wasp-107b and its quartz clouds and the rogue worlds of the Orion Nebula have already been scrutinized along with a host of other exoplanets.
‘Having found all these worlds, we are now in the fortunate position of being able to study them in detail, analyze their atmospheres and even map their features, whereas 30 years ago we weren’t sure if they were at all existed,” he says. astrophysicist Prof. Jayne Birkby from the University of Oxford.
An early target for astronomers using the JWST was Trappist-1, a small, cool star of the type known as a red dwarf. Forty light years from Earth lies a family of seven small rocky worlds, three of which lie in an area known as the habitable zone. Here, conditions are neither too hot nor too cold to prevent water from existing as a liquid, a prerequisite for life to flourish, astrobiologists say.
However, analyzes – using the JWST – of two of the star’s inner planets, Trappist-1b and Trappist-1c, have shown that they have no or only a very thin atmosphere. Further JWST studies of the rest of the system are now being planned. “The Trappist-1 system still looks promising if you’re looking for a world that might support life,” says astronomer Dr Jo Barstow of the Open University.
However, there is one special problem that affects studies of stars like Trappist-1. Red dwarfs are spotty. This may not sound like a terminal condition, but it does have serious consequences, Barstow added. “Our own sun has sunspots associated with intense solar activity, but they are relatively few. Trappist-1, on the other hand, has dozens of spots that are constantly changing, making it very difficult to distinguish between these and features of a planet’s atmosphere. The Trappist-1 system will not reveal its secrets easily.”
Ultimately, astronomers using the JWST to look for signs of extraterrestrial life are looking for a series of biological markers known as the Big Four: oxygen, carbon dioxide, water and methane. Their presence in an exoplanet’s atmosphere would be a strong sign that some life exists there.
“The exact proportions would vary, however,” Birkby said. “The Earth has an atmosphere that is 21% oxygen, but that would have been very different 2.5 billion years ago when there would have been very little oxygen. The great oxidation event – which occurred when cyanobacteria in the oceans began producing oxygen through photosynthesis – had not yet begun. However, there was still life on Earth at that time.”
What scientists will make of a world whose atmosphere contains all the Big Four remains to be seen. “In current Earth quantities it would be hard not to get excited,” Birkby added.
Others, however, are sounding a note of caution. “Even if you get a perfect profile of gases and water vapor in the atmospheres of exoplanets, you will still only be making indirect measurements, and to say that you have definitively found life on that basis is difficult to justify,” says Barstow .
“Even if you were 99% certain of the claim, there would still be a nagging doubt that what you observed was due to non-biological phenomena.”
The life of the James Webb Space Telescope promises to be an intriguing one – and a long one. JWST’s flight, on an Ariane 5 rocket, from the European Space Agency’s launch pad at Kourou in French Guiana to its current position in orbit around the sun was virtually flawless. The observatory used very little fuel to maneuver itself to the exact target location – and that means there will be extra fuel to keep the telescope oriented for much longer than expected. Aerospace engineers have calculated that the expected lifespan of the JWST could be doubled in ten years.
“In many ways that is very good news,” says astronomer Professor Stephen Wilkins of the University of Sussex. “We will now be able to do a lot more science with it. However, the telescope will decay over the years as it is hit by meteorites and cosmic rays. That will slowly degrade performance, so we have to make the most of it while it is operating under near-optimal conditions.”
Wilkins’ own specialty is the study of galaxies and black holes. “Still, I think the most exciting science that will be accomplished by the JWST concerns exoplanets,” he said. “We’re going to learn so much about the chemistry of their atmosphere and discover some very strange and bizarre worlds out there. It is extremely exciting.”