The James Webb Space Telescope (JWST) has taken its first direct image of a planet orbiting a distant star. The planet, known as HIP 65426 b, is a gas giant several times larger than Jupiter, orbiting its star at a distance three times greater than the distance between Neptune and our sun. HIP 65426 b is only about 15 million years old – astronomically newborn – and about 350 light years from Earth.
You may not be impressed by the level of detail in these new planetary images, but the researchers who took the images certainly were. “I had to make sure I wasn’t looking at a simulated image,” says Sasha Hinckley, a professor of astrophysics at the University of Exeter in England who helped lead the study, when the results came back. “It looked like the pictures of the model when we wrote our proposal five years ago.”
HIP 65426 b images reveal that JWST is exceeding expectations for studies of exoplanets, which are one of the telescope’s four central research areas. This means that JWST’s scheduled attempts to observe other exoplanets will likely be more successful than the researchers had hoped, and that astronomers could become more ambitious when submitting proposals to the JWST Board of Directors in future research cycles.
The JWST is not the first telescope to take direct images of the exoplanets, but it is already proving to be the best. Hinckley has seen the field evolve: he’s been working on imagery of exoplanets for nearly 20 years. “I was really impressed by the technical challenges of this research – from having to block out these incredibly bright host stars, which are 10,000 or a million times brighter than the faint planets they orbit,” he says.
Such a feat seems almost impossible – like spotting a faint glowing firefly fluttering under the bright stadium light from your seat across the field. However, with the right technique, exoplanets can be detected.
“We can go and observe a nearby star that has similar properties to the target star,” says study co-author Arin Carter, a postdoctoral researcher at the University of California, Santa Cruz, who led Analyze this extrasolar imaging. “Then we can basically build a model of what starlight looks like and put it away to just leave the planet.”
This sounds deceptively simple, but there are a lot of things that have to go right for this method to work. And in this case, they went well – even more than Carter and Hinckley had planned.
The imaging sensitivity of JWST was shown to be greater than expected. The advanced hungraf succeeded in blocking the majority of the host star’s light. And perhaps most importantly for this particular study, the JWST was incredibly stable when its observations were taken. Stability is critical to getting a clean starlight cast from a second star to subtract from the first.
“What we’ve seen is that James Webb is so incredibly stable that [starlight] So the pattern is stable from star to star,” Hinckley says. “And this is really due to the amazing work that has actually been done by thousands of scientists, technicians, and engineers over the past 20 years all over the world.”
Charles Beechmann, director of NASA’s Exoplanet Science Institute, helped develop the JWST research tools that Hinckley and Carter used for the imaging. He says, “When you launch something, you build it according to a set of requirements. And then you have a set of what we call ‘desires’.”
Thanks to the latest images of the exoplanets, it is now clear that the JWST instruments meet everyone’s wishes. “You have tighter images; you have less tension. The detectors do a little better,” says Bechman. Because of its level of sensitivity and proven stability, JWST has the ability to directly observe much smaller exoplanets than any other telescope in the past — even smaller than it had hoped researchers.
This is excellent news for future studies, including one that Beichman will command between July and August 2023 that will use direct imaging to search for planets within our nearest star system, Alpha Centauri.
So far, astronomers have only been able to image exoplanets that are several times larger than Jupiter and orbit very far from their stars. “But what we now know from these observations is that James Webb will most likely lead us to our isotopes of Saturn or perhaps our Neptune to the nearest stars,” Hinckley says.
Sebastian Marino, a research fellow in astronomy at Jesus College, University of Cambridge, is one likely beneficiary of the JWST’s astonishingly over-performance of expectations. Between April and June, Marino and his colleagues plan to observe stars surrounded by broad debris disks that resemble giant versions of Saturn’s rings. Marino’s team will focus on a few particular disks that contain noticeable gaps, working on the hypothesis that as-yet-undiscovered exoplanets are responsible for “carving” these gaps as they orbit their host stars.
Based on the width of the gaps, Marino predicts that these exoplanets (if any) are about the same mass as Saturn or Neptune. While their discovery began as an ambitious target, the latest imaging results indicate that JWST is capable of detecting planets at those sizes, Hinckley notes.
“The fact that the performance is better than we thought is really encouraging,” Marino says. And even if JWST doesn’t find the exoplanets it’s hoping for, Marino is happy that the telescope will be able to confirm that they don’t exist. (An important, but often overlooked, aspect of searching for planets is knowing when to stop searching for worlds around any given star.) Marino says that a weaker telescope would be much more likely to produce inconclusive results that only extend what would ultimately be useless. Search.
The latest images of exoplanets also bode well for Elizabeth Matthews, a postdoctoral researcher at the University of Geneva. “For my own software, we are sure to see that the tool will really work as we expected when we designed the software,” Matthews says.
Between April and May 2023, Matthews will use the James Webb Space Telescope to observe a nearby star that holds a planet – Epsilon Indy A, just 12 light-years away. This star’s exoplanet, Epsilon Indy Up, is known only by the subtle wobbles in gravity that its size induces on the star. No one has seen this planet firsthand, but astronomers’ best estimates suggest that it must have been fairly cold, which means it’s fairly old. Giant exoplanets are believed to be hot and radiate huge amounts of thermal energy left over from their recent creation. (The glowing planetary bubble seen in infrared images of HIP 65426 b at JWST is mostly heat energy emitted by the planet itself, not light reflected from the tops of its clouds.)
The older, cooler planets were generally too faint to image – drowned out by the bright light of their host stars. Thus, Matthews’ plan to image a more mature planet is challenging, but JWST’s recent performance indicates that it should certainly be possible. Matthews says she designed her study to take the minimum time needed to be able to produce a planetary image — but is now more confident that it will succeed in that time frame because the JWST’s greater-than-expected sensitivity is like giving more observation time.
It’s too late to easily change plans for the JWST’s opening “cycle 1” observations to take advantage of higher-than-expected high-contrast imaging performance, but these early results will certainly make astronomers more confident when planning future research. Marino and Matthews both suggest that they might set bolder research goals next time. Research proposals for the second cycle of feedback are scheduled to be submitted at JWST in late January.
Before then, Sasha Hinckley plans to reach out to the astronomical community with advice on how to make the most of the James Webb Space Telescope based on his team’s updated understanding of its capabilities. “We expect that our recommendations will enable the community to come up with the strongest possible set of suggestions for making these observations,” Hinckley says.
In future research cycles, targets deemed too small or out of reach may be considered within reach. Ultimately, JWST’s ultra-imaging work of extrasolar planets should help guide efforts to develop more ambitious observatories that can image not just gas giants but smaller and fainter targets: potentially habitable and more Earth-like worlds.
The proposals that were ‘cool, she’d be lucky if we could do that’ enter the realm of ‘yes, we should be able to do this,’ and a new set of things that were ‘there’s no way we can do this’ enter the realm,” says Bechman. Yes, we have a chance to make it happen.”
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