When you think of the results from NASA’s James Webb Space Telescope (JWST), images of swirling colorful clouds in nebulae, galaxies older than we’ve ever seen before, and infant stars being born probably come to mind. In its first year in space, results from NASA’s new powerhouse telescope have graced the cover of Scientific American, billboards in Times Square, and the computer screens of avid astronomy enthusiasts and casual readers alike. Viewers across the world, including even the president of the United States, have marveled at the cosmos as seen by this marvelous machine.
Yet, one of JWST’s most incredible results has slipped by mostly unnoticed and underappreciated. You may have missed it, or even dismissed the image as a drab dot—nothing near the splendor of sights like the Carina nebula.
I believe the most exciting JWST result yet is that dot—the telescope’s first image of an exoplanet, a planet around another star.
Sure, maybe I’m a little biased as an astronomer whose research focuses on this precise topic. But hear me out; I quite literally shouted in joy at my computer upon seeing that first image.
Those small lumpy blobs are light from an actual planet, one almost 10 times the size of Jupiter and almost 400 light-years from Earth, known as HIP 65426 b. It orbits a star much larger than our sun, and is very young—so young, in fact, that it’s still warm from the primordial heat of its formation, glowing brightly in infrared light. Those infrared photons traveled directly from another world to reach JWST’s magnificent golden honeycomb mirror, creating the images we see. They are so much more than simple dots.
It’s incredible that humanity has managed to directly view another planet—a task likened to photographing a firefly buzzing amid a city’s lights from hundreds of miles away. Planets are extremely faint compared to the bright stars they orbit, so to view them we must sift through the starlight to uncover the planets underneath. Astronomers solve this problem by filtering starlight with an item known as a coronagraph, which blocks out the bright central area of the star, and by keeping images steady and crisp with adaptive optics technology.
The first directly imaged planet was 2M1207b, a gas giant five times larger than Jupiter, discovered in 2004 by a telescope high in the Chilean desert. Around 10 years later, the smallest directly imaged planet to date was discovered: 51 Eridani b, only two times the size of Jupiter. Direct imaging is currently limited to these sorts of larger planets. While telescopes like Kepler and TESS, which find planets by searching for small dips in starlight, called transits, have discovered thousands of exoplanets, direct imaging’s tally hovers around a mere 50.
Given the difficulty, why is direct imaging appealing? Because exoplanets’ orbits are beautifully on display with direct imaging, for starters. There’s no need to disentangle complicated secondary signals as with many other detection techniques—instead, you can simply watch the planets move, like those within the HR 8799 system, a scaled-up version of our outer solar system.
More important, direct imaging gives a unique window into exoplanets’ atmospheres through spectra. Spectra are astronomers’ most prized tool for exploring the cosmos, since they provide information on the chemical makeup of celestial objects, their temperatures, magnetic fields and so much more. A spectrum is simply the light from an object spread out into a whole rainbow—and usually, some chunks of the rainbow are missing. Those are clues. As atoms absorb light, they create spectral lines specific to the element absorbed, creating a distinct fingerprint for each chemical. Exoplanet spectra reveal what’s going on in a planet’s atmosphere, even including possible signs of life.
JWST’s first exoplanet image, released last fall, was followed by the first direct spectrum of an exoplanet in March, described as the “highest fidelity spectrum to date of a planetary-mass object.” Although this exoplanet, VHS 1256b, is far from habitable—it’s a tormented world of hot, sandy winds—its exquisite spectrum proves how much information we can now obtain for distant worlds, far beyond previous capabilities. JWST has the distinct advantage of being in space, above Earth’s pesky atmosphere; the air around our planet blurs images and blocks out certain wavelengths of light, like longer-wavelength infrared, which are extremely useful for directly characterizing exoplanets. The space telescope also can resolve details in planetary spectra around 100 times finer than previous direct imaging instruments on the ground.
JWST’s first directly imaged planet and first direct spectrum of a planet-sized object are both huge steps forward for direct imaging, the underdog of exoplanet detection, showing its promise. As we search for life and move towards holistically characterizing planets instead of simply identifying them, direct imaging will drive new discoveries.
Although other exoplanet-hunting methods (such as transit spectroscopy) can retrieve spectra, high-contrast imaging is unparalleled in its ability to peer past clouds and obtain atmospheric data in pristine detail. That will be crucial to the hunt for biosignatures, signs of life—a goal so important that a major committee from the National Academies, known as the Decadal Survey on Astronomy and Astrophysics, recently identified the search for habitable worlds as a top priority for the entire astronomical community.
The Decadal Survey also mapped out two main telescope projects with high-contrast imaging as a key capability: the extremely large telescopes (ELTs) on the ground, and a large ultraviolet, optical and infrared space telescope. ELTs are the next generation of major telescopes on Earth, with mammoth mirrors around 30 meters or more in diameter, such as the Thirty Meter Telescope, the Giant Magellan Telescope and the European Extremely Large Telescope. These facilities will be a huge improvement on our current largest optical telescopes like the Keck Observatories in Hawaii, which are around 10 meters in diameter.
To build a mirror that large, engineers must combine separate mirror segments into a honeycomb shape, like JWST’s famous golden mirror. Such a complex contraption introduces more engineering challenges than a solid mirror, requiring scientists to align all the segments with painstaking precision. Although we have years of practice with this technology on the ground, JWST is our first major test of a segmented mirror in space, and it’s performing beautifully—a step in the right direction for these future large observatories.
NASA is also already planning for its next major space observatory, the Habitable Worlds Observatory (HWO), hopefully coming in the 2040s. Both the ELTs and HWO aim to take the first images of an Earth-like exoplanet and will build off current direct-imaging technology developed for observatories like JWST. The observations taken now with JWST are important pathfinders for exoplanet science, too, as astronomers will need to learn as much as possible about exoplanets now in order to choose the best targets for HWO.
Direct imaging is the future of exoplanet exploration, and quite possibly how we’ll find the first signs of extraterrestrial life. The first directly imaged planets from JWST are a monumental step on the thrilling path ahead of us. Although they might appear as inconsequential dots, they promise the fulfillment of our wildest sci-fi dreams.
This is an opinion and analysis article, and the views expressed by the author or authors are not necessarily those of Scientific American.