Researchers image known planet 51 Eridani b in Webb data

Researchers have recovered the first image of the known giant planet 51 Eridani b at 4.3 micrometers, an infrared wavelength where standard processing had failed to detect it, from James Webb Space Telescope observations.

The team used a method called Physics-based Learning for Imaging Planets, or FLIP, on observations from Webb’s Near-Infrared Camera. In a paper published in Nature, the researchers say their method improved sensitivity to faint planets by 2–15 times over standard processing across the tests; the gain varied with the observation and the distance from the star.

Analysis

Removing the star’s glare

A star’s glare can overwhelm the faint light of a planet orbiting it. Conventional processing estimates that glare from reference observations and subtracts it, but changes in telescope pointing and temperature can alter the pattern between observations. The remaining glare can hide a planet.

As The Register explains, FLIP instead models how light passes through the telescope. It uses measurements of the incoming light to simulate the glare, calibrates that model against a reference observation, then adjusts it to fit the image under study before subtracting the modeled glare.

The method uses automatic differentiation to calculate efficiently how changes to the model affect its fit, enabling researchers to repeatedly adjust it through gradient descent beyond the glare patterns available in reference images. To reduce the risk of removing real planet light along with the glare, they also add artificial planets and track their signal-to-noise ratio as the model is adjusted, stopping when it peaks or plateaus. The artificial planets also serve in recovery tests to quantify signal loss.

Limits and next steps

The authors say FLIP has not yet reached the fundamental sensitivity limit set by photon noise—the random variation in detected light—in any of the observations tested. They identify reducing computational cost and handling the larger data volumes from ground-based observations as areas for further work.

The new image covers a wavelength range that includes a carbon dioxide absorption band and cannot be measured from the ground because of Earth’s atmosphere. The researchers plan to measure the planet’s brightness at that wavelength and use it for further study of its atmosphere.