New method shows the known planet 51 Eridani b at 4.3 microns

A team led by Northwestern University has found the giant planet 51 Eridani b in images the James Webb Space Telescope had already taken, at a wavelength of 4.3 microns where the standard way of removing starlight had not found it. It is the first image of the planet at that wavelength. The planet itself is not new: it was first found with telescopes on the ground.

The study, led by Rodrigo Ferrer-Chavez with colleagues at Caltech, MIT and the Space Telescope Science Institute, was published in Nature on November 4, 2026. Its subject is less the planet than the method that found it, which the team calls FLIP.

Subtracting a star's glare

A planet next to its star is lost in the star's glare. Webb's NIRCam camera carries a coronagraph, a mask that blocks most of the starlight, but the leftover glare still has to be modeled and subtracted from the image before a faint planet shows up.

The standard method, called KLIP, builds its model of the glare from images of other stars, known as reference stars. The telescope changes slightly between the reference picture and the target picture, and those small changes limit how faint a planet KLIP can find.

FLIP also starts from reference stars, but it adds a physical model of the coronagraph's optics. The team first calibrates that model on the reference images, then lets it adjust for small changes in the telescope's aberrations, the tiny flaws in how its optics focus light, until it better matches the target image. The team tuned about a million model parameters this way. Northwestern's news release calls the result a digital twin of the telescope.

From a miss to a detection

The team tested FLIP on Webb images of three stars. Two, HIP 65426 and 51 Eridani, have known planets. The third, TYC 5899, has none, so the team planted fake planets in its data to measure how much fainter a planet FLIP could pick out.

On these published Webb data, FLIP was 2 to 15 times more sensitive than the standard method as used in the original analyses. At the position of 51 Eridani b in the 4.3-micron image, sensitivity improved by a factor of about four, and the planet appeared with a signal-to-noise ratio of 6.3, a measure of how strongly it stands out from the leftover noise. In the original analysis, the standard method had detected the planet at 4.1 microns, but not at 4.3 microns or at longer wavelengths.

Why it matters

Light at 4.3 microns is infrared, far beyond the colors our eyes can see. It is where carbon dioxide absorbs light, and Earth's own atmosphere blocks that wavelength for telescopes on the ground, so only a telescope in space like Webb can look there. The team plans to measure the planet's brightness in the new image and use it to study its atmosphere and how it formed.

The method could matter more for the future. To image planets like Earth, the proposed Habitable Worlds Observatory may need optics 100 to 1,000 times more stable than Webb's. If FLIP can be extended to the much fainter planets such a telescope would hunt, the authors write, that stability requirement may be partially lifted.

What is not settled

The gains were measured on three stars, all observed with one instrument, Webb's NIRCam coronagraph. A model this flexible can also remove some of a planet's own light, the authors found. They planted fake planets in each image to measure that loss and stopped the fitting early to limit it, and farther from the star FLIP sometimes lost more planet signal than the standard method.

The benefit for a future Earth-imaging telescope is conditional, and the authors say it holds only if FLIP can be extended to the much fainter planets such a telescope would look for. The new detection of 51 Eridani b is a first step, and the measurements of its atmosphere at 4.3 microns are still to come.