The James Webb Space Telescope captures a spectacular image of a newborn planet.

If a single field of study were to be chosen as representative of modern astronomy, it would undoubtedly be the search for exoplanets, with the ultimate goal of finding life on one of them or even, why not, a "second Earth." All these distant worlds (close to six thousand at the time of writing) also offer an enormous amount of information about the intricate mechanisms that govern the formation of planetary systems, including our own. For decades, detecting these elusive celestial bodies has been a Herculean task, but the arrival of the James Webb Space Telescope four years ago marked a turning point. And now, despite the telescope having already discovered other exoplanets in 2022 , 2023, and 2024 , the James Webb has just obtained an exceptional direct image of a young exoplanet embedded in the debris disk surrounding a newborn star. This is the direct image of the smallest exoplanet detected so far using this technique.

The discovery, made by French astronomer Anne-Marie Lagrange of the CNRS at the Paris-PSL Observatory in collaboration with the Université Grenoble Alpes and recently published in Nature , is yet another example of the seemingly infinite capabilities of the space telescope. Named TWA 7 b, the new planet is the lowest-mass planet observed by direct imaging to date, an achievement that represents a major step forward in the detection and characterization of increasingly smaller, and therefore more Earth-like, worlds.

But why is direct imaging of an exoplanet so extraordinarily difficult? The answer lies in the intense light of stars and the small size of planets compared to them. Directly viewing an exoplanet would be like trying to see a firefly dancing around a lighthouse several kilometers away. The lighthouse is the star: its brightness is so overwhelming that it completely drowns out the faint light of any planets orbiting it. That's why the vast majority of exoplanets discovered so far have been detected through indirect methods, such as transit (when a planet passes in front of its star, causing a slight dimming of its light) or radial velocity (which measures the 'gravitational wobble' a planet causes on its host star).

However, these techniques don't provide a true image of the planet. This is something that direct imaging does, which seeks to capture the planet's own light, either reflected from its star or, more commonly, its own residual heat, which can be observed in the infrared.

And this is where James Webb's extraordinary infrared capabilities come into play. To overcome the problem of starburst, Lagrange and his colleagues used a novel coronagraph (made in France) installed on the telescope's Mid-Infrared Instrument (MIRI), a powerful infrared detector. Just as during a total solar eclipse the Moon blocks its light and allows scientists to study its otherwise invisible atmosphere (the corona), a coronagraph is essentially an opaque disk, or mask, placed on the telescope to block the light from a distant star while observing it. This maneuver allows the much fainter light from objects close to the star, such as exoplanets or debris disks, to be detected by the infrared instrument.

MIRI's coronagraph on Webb, however, is not a simple dish, but incorporates a host of advanced technologies, including a Lyot-type coronagraph and three four-quadrant phase mask (4QPM) coronagraphs. These masks allow for a much smaller 'internal working angle'. This means they can block the star's light at very close angular distances, making it possible to observe planets orbiting much closer to their star than previously possible.

The observation process with MIRI's coronagraph is extremely meticulous. After blocking most of the starlight, there are still traces of reflected light that can interfere with observations. To eliminate this residual light and obtain a sharper image of the exoplanet, astronomers use the "reference star subtraction" technique. This involves observing a nearby, planet-free reference star, using exactly the same instrument configuration. By subtracting the image of the reference star from the image of the target star (the one with the exoplanet), researchers are able to isolate the faint signal from the planet.

As if that weren't enough, Webb also employs a technique called Angular Differential Imaging (ADI), which involves rotating the telescope slightly during observation. This causes the planet to move in the field of view while the telescope's residual light patterns remain static, making them easier to eliminate later. Thanks to the combination of these methods, the telescope can detect objects up to a million times fainter than the star itself.

The study's authors focused their attention on targets that seemed most favorable for direct imaging. These were young systems, only a few million years old, that could be observed "from the pole" (i.e., their disks seen "from above"), which is very important because newly formed planets in these disks are still hot and therefore emit more infrared light, making them "brighter" to Webb's instruments than older, cooler planets would be.

Among the several disks that could be observed face-on, two particularly attracted researchers' attention, as previous observations had already revealed concentric ring-like structures within them. This led to the suspicion that these structures were the result of the gravitational interaction between unidentified planets and small rocky and icy bodies ('planetesimals'), precursors to planets that collide and clump together in protoplanetary disks. One of these systems, called TWA 7, stood out from the others due to its three clearly distinguishable rings, one of which is particularly narrow and surrounded by two empty areas with almost no matter.

The image obtained by James Webb revealed a source of infrared light right in the heart of the narrow ring. After carefully ruling out the possibility of observational biases (such as the presence of a background star or an instrument artifact), Lagrange and his team concluded that it was most likely an exoplanet. Detailed simulations confirmed the hypothesis: a planet of the estimated mass and position could indeed create a thin ring and a "gap" exactly where it was observed.

The new exoplanet, dubbed TWA 7 b, is a true lightweight compared to the giant worlds that have been directly imaged so far. In fact, it is up to ten times lighter than previously directly imaged exoplanets. Its mass, comparable to that of Saturn, is approximately 30% that of Jupiter, the most massive planet in our Solar System. This means that, while still a gas giant, TWA 7 b is significantly less massive than many of the "hot Jupiters" or "super Jupiters" that dominated the lists of directly imaged exoplanets. For example, systems like HR 8799, which hosts four directly imaged giant planets (the first of which, Beta Pictoris b, was discovered in 2008), are significantly more massive than TWA 7 b. Even Epsilon Indi Ab , discovered in 2024 by Webb himself with his MIRI instrument and one of the coldest exoplanets we have direct images of, has several times the mass of Jupiter.

The new result, therefore, marks a new stage in the detection of increasingly smaller exoplanets by direct imaging. Worlds that are more similar to Earth than to the gas giants in our own Solar System. While TWA 7 b is not a "super-Earth," its mass of approximately 0.3 times that of Jupiter (about 100 times the mass of Earth) places it in a significantly lower range than the giants previously detected using the same method.

The limits of the James Webb Space Telescope, however, have not yet been reached. In fact, scientists hope to capture images of planets only 10% the mass of Jupiter, and therefore even closer to the mass of Earth. Added to this are the new capabilities that future generations of telescopes, specifically designed for the search for exoplanets, will have. Not surprisingly, astronomers already have a list of the most promising systems for these future observations.