Astronomers used the James Webb Space Telescope (JWST) to try to directly image young giant planets that were suggested by gas motions seen with ALMA. They targeted five well-studied protoplanetary disks and used a mid‑infrared coronagraph to block starlight and look for faint companions. The main result is a non-detection of any point source that would match the previously inferred protoplanets.

The team observed HD 163296, RXJ1615.3–3255, RXJ1842.9–3532, SY Cha, and LkCa 15 with JWST’s Mid-Infrared Instrument (MIRI) using the F1140C filter at 11.3 microns. The targets were chosen because earlier ALMA observations of carbon monoxide (CO) gas showed local departures from the expected orbital motion. Those departures, or kinematic perturbations, have been interpreted as the gravitational wakes of forming giant planets at wide separations (roughly 70–300 astronomical units).

To see faint planets next to bright stars, the observers used a coronagraph with a four-quadrant phase mask (a device that suppresses the star’s light) and a careful subtraction of the star’s point spread function (PSF) — the pattern of starlight left in the image. They combined standard reference‑star subtraction with forward modeling of light coming from partially resolved inner disk material. Because inner disk emission can change the star’s diffraction pattern, this extra modeling was needed to improve sensitivity near the star. The team also expanded their library of reference stars to help remove residual starlight.

No compact source consistent with an embedded protoplanet was detected in any of the five systems. Instead, three disks show extended 11.3‑micron emission that traces the outer disk out to radii similar to those probed by ALMA’s CO maps. The authors ran injection tests — they added fake planets to the data to see what would be detectable — and derived upper mass limits of roughly 3 to 20 Jupiter masses at separations of a few hundred AU. Those limits assume there is no extra heat coming from material immediately around a forming planet (a circumplanetary environment).