The Carina nebula is a cloud of gas and dust where new stars are born. Denser parts collapse under gravity, forming protostars that draw more material into a disk from which planets form.NASA; ESA; CSA; STSCI
Pictures showcase start of science campaign for NASA’s largest space telescope
At long last, eager astronomers—and the public—get to view snapshots of the universe provided by the James Webb Space Telescope, the largest, most complex, and most expensive space telescope ever built. Yesterday, in a sneak preview, the White House released one picture, a deep image bristling with thousands of distant galaxies. Today, NASA
released four more that demonstrate Webb’s ability to scrutinize gas clouds and planetary systems closer to home.
The images—a product of Webb’s giant, majestic, gold-plated mirror—are not only sharper than those of the Hubble Space Telescope, but are also essentially different, capturing the longer, infrared wavelengths that are important for many branches of astronomy. For Webb’s engineers and designers, who have endured years of delay and a nerve-wracking 6 months of launch, deployment, and commissioning, the relief is palpable. “I’m feeling a mix of excitement and emotion. [Webb] has really delivered, and there will be a rush of new discoveries,” says Brant Robertson of the University of California (UC), Santa Cruz, who helped develop Webb’s near-infrared camera.
For most astronomers, the wait isn’t quite over yet, as their scheduled observations may not happen for weeks or months. Exoplanet researcher Laura Kreidberg of the Max Planck Institute for Astronomy (MPIA) is one of the lucky ones. As part of a large collaboration doing “early release science” with Webb, she’ll get to see their first tranche of data in 2 days. Nevertheless, “It’s a long wait from Tuesday to Thursday,” she says. But come Thursday afternoon when the data start to pour in, “I’ll make a big pot of coffee, put out some snacks, and we’ll sit and look at it.”
Originally conceived in the 1990s and built with European and Canadian contributions, Webb at times seemed like a cursed mission, buffeted by cost overruns, schedule slips, and technical hitches. Beset by criticism, “It was hard to keep the team at the edge of excellence,” NASA science chief Thomas Zurbuchen said at a recent briefing. But after a flawless launch on 25 December 2021, those trials are almost forgotten. “I don’t think any of us expected how well it went,” Zurbuchen says.
The accuracy of the launch, on a European Ariane 5 rocket, meant Webb didn’t have to use much fuel for course corrections and now has more to keep itself in a gravitational pocket on the opposite side of Earth from the Sun, about 1.5 million kilometers away. Planned as a 10-year mission, Webb is now expected to last at least twice as long.
The launch of the $10 billion instrument did not end the tension. To unfurl its giant sunshield, swing six of the 18 segments in the 6.5-meter-wide mirror into position, and extend the secondary mirror on its booms, engineers had to navigate some 300 steps, any one of which could have doomed the mission. “Every day the risk level has gone down and my ability to sleep has increased,” says Charlie Atkinson, the project’s chief engineer at Northrop Grumman, NASA’s prime contractor for the mission.
Tiny motors adjusted the position, tilt, and curvature of the mirror segments by fractions of a hair’s breadth until they could together focus on targets as a single mirror. Operators then had to check out Webb’s four instruments, a mix of cameras and spectrographs, which split incoming light into its component wavelengths. “We have an observatory in excellent shape, that meets or exceeds expectations,” Bill Ochs, Webb’s project manager at NASA’s Goddard Space Flight Center, announced today.
Not everything went according to plan. Some computer glitches required a few hours’ pause. The mirror has been dinged by a handful of micrometeorites—that was expected but one was larger than models predicted and operators are working to mitigate its impact. “There have been some issues,” Ochs says. “But when you have a good team, you can get through it.”
By 21 June, Webb was taking data for the 286 teams of scientists who had been allotted time on the telescope in its first year, known as cycle one. “We’ve got some amazing science in the can,” Zurbuchen says. Researchers have reported seeing that some of their scheduled observations have taken place, but NASA sat on the data until this week, when commissioning officially ends. Now, Atkinson says, “We hand over the keys. It’s ready. Go do science.”
The pictures and spectra released today are the result of a yearlong selection process that Zurbuchen calls “bottom-up.” NASA wanted to show off the telescope’s capabilities and offer a taste of the different fields of astronomy it will transform. So managers asked the instrument and science teams for a range of targets that would show “the best of this thing,” Zurbuchen says. Some 70 were suggested and these were whittled down by a committee to the five released so far.
Stephan’s Quintet is a compact group of four galaxies with another in the foreground. Filaments of glowing gas are signs of shock waves as the galaxies interact. One day the four will likely merge.NASA; ESA; CSA; STSCI
The Southern Ring nebula is a glowing shell of ionized gas blown off by a giant star at the end of its life. A white dwarf at its center—the stellar cinder of the giant—emits ultraviolet light that causes the nebula to fluoresce.NASA; ESA; CSA; STSCI
SMACS 0723 is a deep field containing thousands of galaxies. The gravity of galaxies in the foreground acts as a lens to magnify and distort more distant galaxies.NASA; ESA; CSA; STSCI
One picture, of the galaxy cluster SMAC 0723, showcases Webb’s ability to peer into the most distant corners of the universe and hence the furthest back in time. It shows a field crowded with thousands of galaxies, some with shapes distorted by the intense gravitational field of a galaxy cluster in the foreground. A spectrum from a 13.1-billion-year-old galaxy in the image showed it contained oxygen, hydrogen, and neon—the most distant galaxy for which we know the constituents. Dominika Wylezalek of Heidelberg University calls the image “mind-blowing.” “The level of detail is really breathtaking.”
Hubble saw much further back than its designers ever imagined, spying a galaxy that existed just 400 million years after the big bang—3% of the universe’s current age. But Webb will see many more galaxies that are even younger, not just because of its larger mirror, but also because of its sensitivity to infrared light. Photons emitted by the earliest stars are stretched in their journey by the expansion of the universe, pushing them into infrared wavelengths that Hubble cannot see. Previously, says Sarah Bosman of MPIA, “We could only see the very bright galaxies, and the biggest. With Webb, we’ll see the whole array.”
Galaxy surveys will help astronomers understand the early history of these agglomerations: when they started to form stars and how quickly they organized into the disklike spirals such as the Milky Way. “Webb is capable of filling in the gaps,” Robertson says. Webb will also help figure out what ionized the neutral hydrogen gas that filled the universe before the stars turned on. By the time of the universe’s billionth birthday, that hydrogen was ionized. Astronomers think this was mostly the work of high-energy ultraviolet photons from the first generation of stars, which were huge and bright and made solely of this primordial hydrogen. But Hubble hasn’t seen enough early galaxies to account for the needed photons. “Webb is the only facility that can see” this early era, Robertson says.
Another one of the released pictures is of the well-known Stephan’s Quintet, a cluster of four interacting galaxies 290 million light-years away that sits behind a fifth galaxy in the foreground. Seen with Webb, it is possible to discern glowing gas and dust heated by two of the merging galaxies and areas of active star formation generated by that turmoil. “It is this sort of interaction that drives the evolution of galaxies,” says Giovanna Giardino of the European Space Agency.
Alice Shapley of UC Los Angeles will use Webb’s near-infrared spectrograph (NIRSpec) to tease apart the light from galaxies to find out how hot they are, how they’re moving, and what they’re made of. She’s interested in faint emission lines from interstellar oxygen gas, which show up as spikes in spectra. The oxygen is created in massive stars and scattered when they die. “It tells you how many stars are made,” she says, and is a good marker for the flows of gas in and out of a galaxy.
The information will help researchers understand why some galaxies are prolific creators of stars, whereas others are subdued or even dead. Earth’s atmosphere clouds the view of these oxygen lines for most ground-based spectrographs. NIRSpec uses a mask covered with tiny shutters to gather light and generate spectra from dozens of galaxies simultaneously, which should increase the number of galaxies with known oxygen lines by an order of magnitude. “Webb allows us to go so much further,” Shapley says. “It’s going to be amazing.”
Misty Bentz of Georgia State University will test a different NIRSpec capability: taking a spectroscopic “image” in which every pixel has its own separate spectrum. Her project involves staring for 9 hours at a single galaxy, the nearby NGC 4151—dubbed the Eye of Sauron because of the eerie glow of the supermassive black hole at its heart, which shines brightly as it heats up gas being drawn into its maw. Bentz will look for subtle changes to the spectrum of the swirling gas that reveal the black hole’s mass, showcasing NIRSpec’s ability to take faint spectra of the gas while blocking the bright area around the black hole itself.
Webb will also study targets within the Milky Way—objects like the Carina nebula, one of today’s released pictures. Webb’s image of the vast stellar nursery, 7600 light-years from Earth, contains hundreds of newly born stars that have never been seen before, as well as swirling dust and gas buffeted by stellar wind. Hubble also imaged this local landmark, but Webb’s image has “so much more detail,” says NASA deputy project scientist Amber Straughn.
Within such stellar nurseries, dense clumps of gas gradually collapse to form stars. Melissa McClure of the Leiden Observatory will use Webb to peer into such clouds to see whether they are factories for complex molecules that could give life a head start even before star and planet formation begins. Hundreds of different molecules have been detected as gases, but gases don’t react efficiently unless frozen onto solid interstellar grains of dust. The grains are like singles bars, McClure jokes, where atoms and simple molecules go to join up. So far, only methanol ice has been detected in space, but McClure expects Webb will routinely find ices for molecules such as methane and ammonia. The real prize would be finding complex carbon-based molecules with more than six atoms, such as ethanol or acetaldehyde. “A conclusive detection would be really awesome,” McClure says.
Among NASA’s offerings this week, the most tantalizing taste of what’s to come is the spectrum of an exoplanet. It’s from a giant planet known as WASP-96b orbiting close to a star 1150 light-years from Earth. During regular passes in front of its home star, some starlight is absorbed by gases in WASP-96b’s atmosphere, leaving telltale dips in the star’s spectrum. Theoretical models suggest carbon monoxide and dioxide, as well as methane, may be present, but Hubble and ground-based telescopes couldn’t see them. The first spectrum of WASP-96b shows clear signatures of water vapor in the planet’s atmosphere, and features that indicate the presence of clouds and vapor haze. Astronomers will have to wait for future transits to see what else is there. “I’m really excited to see if the predictions bear out,” Kreidberg says.
Using the Hubble and Spitzer space telescopes, researchers have only been able to spy water and sodium in exoplanet atmospheres. “It’s been like reading a poem and only seeing every third word,” Kreidberg says. Webb is expected to find a wealth of molecules, some of which can hint at a planet’s potential habitability: carbon monoxide and dioxide, methane, ammonia, phosphine, and more. They will be able to probe the atmospheres of every kind of planet from hot Jupiters, through mini-Neptunes, to rocky planets like Earth. “Webb can do everything,” Kreidberg says. Hundreds of exoplanet researchers are preparing feverishly for the expected data deluge from other transiting exoplanets, organizing hackathons and data challenges, and devising data processing pipelines. “We’ve done a huge amount of work to make sure we’re ready,” Kreidberg says. “There’s no calm before the storm.”
A small fraction of Webb’s time will go to objects in the Solar System, but for targets so close and so large—from Webb’s point of view—saturating the instruments is a real problem, says Imke de Pater of UC Berkeley. She will study Jupiter’s thin ring, which may still be rippling in the wake of the 1994 impact of Comet Shoemaker-Levy 9. Imaging the faint ring next to the much brighter planet will be a challenge, but she hopes to discover more ripples, which could signal more recent, unseen comet impacts. De Pater’s fondest wish would be detecting new moonlets of just a few hundred meters diameter or less. “That would be a dream,” she says.
For many more, the dream has already come true—an effort that took 30 years and some 20,000 people around the world to bear fruit. “Beyond the science, [Webb] is rekindling a sense of beauty and wonder about the universe that inspired me to become an astronomer,” Robertson says. “I couldn’t be happier.”
