Webb directly images a young giant next to its star

Most exoplanets are known only as shadows. The transit method watches a star dim for a few hours as a planet passes in front of it, and the radial velocity method wobbles the star’s light by the tug of an unseen companion. Direct imaging, which takes an actual photograph of the planet separated from its star, is the hardest of the detection methods, and until 2025 it had only worked for young, massive, self-luminous gas giants sitting far from their host stars. The paper published in Nature on 25 June 2025, led by Anne-Marie Lagrange of the Paris Observatory and the CNRS, reports that the James Webb Space Telescope has broken that barrier by imaging a planet roughly ten times lighter than any directly imaged before.

The target is TWA 7, a young star about 110 light-years away in the TW Hydrae association, formed roughly 6.4 million years ago. It hosts a bright, nearly face-on debris disk with rings and gaps, the kind of disk structure that models predict is sculpted by embedded planets. The team used the Mid-Infrared Instrument on Webb, equipped with a French-built coronagraph that blocks the starlight, to look for a faint companion in the gap between the disk’s first and second rings. What they found is TWA 7b, a sub-Jovian world estimated at about 0.3 Jupiter masses, orbiting at a projected separation of 52 astronomical units from its star.

The sub-Jovian mass is the headline. Every exoplanet directly imaged before 2025 has been at least several Jupiter masses, young enough and hot enough to glow in the infrared with the leftover heat of formation. TWA 7b at 0.3 Jupiter masses is closer to Saturn than to Jupiter, and it sits at the edge of what the MIRI coronagraph can detect. The paper notes that planets as light as 25 to 30 Earth masses would have been detectable if present at 1.5 arcseconds or more from the star, which means Webb’s direct imaging reach is now approaching the regime of Neptune-like worlds, not just gas giants.

Why does this matter? Direct imaging is the only method that can actually measure a young planet’s light spectrum, which constrains its temperature, luminosity and atmospheric composition. Transit spectroscopy, the workhorse of atmospheric characterization, is biased toward planets that orbit close to their stars, because short orbits produce frequent transits. The population of wide-orbit, young, low-mass planets that Webb can now image is almost entirely inaccessible to transits and radial velocity. TWA 7b sits at 52 astronomical units, far beyond the orbit of Neptune, where a transit would be a once-in-a-lifetime event and the radial velocity signal would be buried in stellar jitter.

The discovery also feeds a formation debate. The disk around TWA 7 shows rings and gaps, and TWA 7b sits in the right gap at the right mass to be the object carving it out. Core accretion models struggle to build a 0.3-Jupiter-mass planet at 52 astronomical units in only 6.4 million years, because the disk material is sparse and the accretion timescale is long. Gravitational instability, which forms planets more rapidly in the outer disk, is a natural explanation but requires more disk mass than is typically observed. TWA 7b is the kind of data point that helps choose between the two.

The planet is still a candidate. The paper’s title uses the careful phrasing of evidence for a sub-Jovian planet, and follow-up astrometry to confirm that the object is co-moving with the star rather than a chance alignment is underway. But the detection sensitivity that Webb has demonstrated is the lasting result: a coronagraph in space can now see planets that belong in our own solar system’s outer neighbourhood, orbiting other stars, in the infrared light they glow with as they cool.