by There’s a distant world where quartz crystals float above a warm, puffy atmosphere. The clouds that fill the sky on Wasp-107b, a planet 1,300 light-years from Earth, are evaporated grains of sand, not water droplets.
Then there is GJ1214, the sauna planet. With a mass eight times that of Earth, it orbits its parent star at one-seventh the distance between Earth and the sun and appears to be enveloped in a thick, dense atmosphere containing vast amounts of steam.
Or the giant, Jupiter-sized planets of the Orion Nebula that have been found floating freely in space, in rogue worlds that appear to be unrelated to any parent star – to the emancipation of astronomers.
These strange, remote planets could not be more diverse or different from each other – although they do have one thing in common. Their wonders are now being revealed by the James Webb space telescope (JWST).
Launching on Christmas Day 2021, the $10bn robot observatory is currently changing our knowledge of our galaxy’s planets. “It took six months to set up the telescope and get its systems working properly – meaning 2023 was the first full calendar year in operation,” said astrophysicist Dr Hannah Wakeford, from the University of Bristol. “The results have exceeded all our expectations.”
The JWST is made up of a 6.5-meter, gold-plated mirror; a sun shield the size of a tennis court; and a range of complex instruments cooled to a temperature just a few degrees above absolute zero. These features allow the telescope to look at the heavens in infrared radiation, revealing details of the universe just after its Big Bang birth 13.8bn years ago, and images of stars being born in clouds of dust.
However, the JWST is providing an additional gift to science – its infrared radiation is ideal for studying exoplanets, or exoplanets, as life orbiting other stars is known. In doing so the telescope is sparking an astronomical revolution.
For centuries, the only planets known to humans were the few we could see in our solar system. But was the solar family typical, scientists wondered? Were planets abundant or rare elsewhere in the galaxy? These questions were particularly important because the latter scenario – a cosmic scarcity of planets – would mean that extraterrestrial life would likely be scarce as well.
The difficulty for astronomers was the simple fact that the stars are very bright but planets are much smaller and much dimmer, and could not be detected near their great celestial parents. It was not until the end of the last century that a new generation of highly sensitive cameras, equipped with telescopes and orbiting observatories, were able to detect tiny points of exoplanets as they passed in front of the star.
After the first few of these transit observations were made, discoveries increased dramatically. Today the total number of observed exoplanets stands at 5,566, according to NASA’s extrasolar planet archive.
Hundreds of objects relatively close to Earth are critical and are now ripe for study with the JWST, astronomers say. Wasp-107b and its quartz clouds and rogue life in the Orion Nebula have already been scrutinized along with many other exoplanets.
“Having discovered all these worlds we are now fortunate enough to be able to study them in detail, analyze their atmospheres and even map their features when, three decades ago, we didn’t know for sure if they existed at all,” said astrophysicist Professor Jayne Birkby of the University of Oxford.
An early target for astronomers using the JWST is Trappist-1, a cool little star of a type known as a red dwarf. Forty light years from Earth, it has a family of seven small rocky worlds, three of which lie within a region known as the habitable zone. Here conditions are not too hot and not too cold to prevent water from already existing as a liquid, a key requirement for life to flourish, say astrobiologists.
However, analyzes – using the JWST – of two of the planets furthest into the star, Trappist-1b and Trappist-1c, have shown that they have no atmosphere or only a very thin atmosphere. Further JWST studies of the rest of the system are now being planned. “The Trappist-1 system looks very promising if you’re looking for a world that could support life,” said astronomer Dr Jo Barstow of the Open University.
However, one special problem plagues studies of stars like Trappist-1. Red dwarfs are spotty. This may not seem like a terminal condition but it has serious implications, Barstow said. “There are sunspots on our own sun that are associated with intense solar activity but there are very few of them. In contrast, Trappist-1 has many spots that change all the time and make it very difficult to distinguish these from the features of the planet’s atmosphere. The Trappist-1 system is not going to give up its secrets easily.”
Ultimately, astronomers using the JWST to look for signs of extraterrestrial life are looking for a set of biological markers known as the Big Four: oxygen, carbon dioxide, water and methane. Its presence in an exoplanet’s atmosphere would be a strong indication of the existence of some kind of life.
“However, the exact proportions would vary,” Birkby said. “Earth has an atmosphere of 21% oxygen but it would have been very different 2.5bn years ago when there was very little oxygen. The great oxidation event – which occurred when cyanobacteria in the oceans began to produce oxygen through photosynthesis – had not yet begun. There was still life on Earth at that time, though.”
What will scientists make of a world where the atmosphere of all the Big Four can be seen. “In sizes similar to Earth today, it would be hard not to be excited,” Birkby said.
Others warn, however. “Even if you get a perfect profile of gases and water vapor in an exoplanet’s atmosphere, you’re still only making indirect measurements, and it’s hard to justify life based on those,” Barstow said.
“Even if you were 99% sure of the claim, there would still be a doubt that what you were observing was caused by non-biological phenomena.”
The life of the James Webb space telescope is likely to be an interesting one – and a long one. The JWST’s flight, on an Ariane 5 rocket, from the European Space Agency’s launch pad in Kourou in French Guiana to its current position in orbit around the sun was almost flawless. The observatory used very little fuel to maneuver itself into its precise target position – and that means there will be more to allow the telescope to aim itself much further than expected. Space engineers calculated that JWST’s expected 10-year lifespan could be doubled.
“That’s good news in many ways,” said astronomer Professor Stephen Wilkins, of the University of Sussex. “We’ll be able to do a lot more science with it now. However, the telescope will deteriorate over the years as it is hit by meteorites and cosmic rays. That will slowly degrade its performance so we should make the most of it while it’s operating in the best possible conditions.”
Wilkins’ own specialty is the study of galaxies and black holes. “However, I think the most exciting science the JWST will do is exoplanets,” he said. “We’re going to learn so much about the chemistry of their atmosphere and we’re going to find a strange and strange world out there. It’s really exciting.”
