Imaging exoplanets below the telescope stability limit
Abstract
Exoplanet imaging is the main method for detailed characterization of planets orbiting beyond 1 au (ref. 1) but it requires suppressing the bright glare of the star to see the faint planet light. As well as sophisticated instrumentation2,3, effective image processing is necessary for starlight suppression, which continues to be a substantial limitation4. Standard algorithms use reference images for starlight modelling and thus they are limited by inevitable telescope instabilities that change from reference to science observation5,6. Addressing this challenge will increase the number of planets amenable to direct imaging and will be a notable step towards imaging exo-Earths with future observatories7. Here we present a new physics-based method for starlight subtraction. Our method combines a multistep optimization with a flexible physical model to produce a starlight model, allowing modelling and compensation of instrument instabilities. We use automatic differentiation (autodiff)8 to optimize millions of model parameters. We demonstrate our method on observations from the James Webb Space Telescope (JWST) Near-InfraRed Camera (NIRCam)9, 10–11 coronagraph instrument. We achieve sensitivity 2–15 times superior to standard techniques, including the first detection of 51 Eridani b (ref. 12) at 4.3 μm. This is the first time, to our knowledge, that such an approach has demonstrated substantially improved sensitivity on real, on-sky coronagraphic imaging. Our framework can be extended to other current and future ground-based and space-based observatories, including the Nancy Grace Roman Space Telescope and the Habitable Worlds Observatory (HWO), potentially relaxing the unprecedented stability requirements needed to make these a success. A new physics-based method combining the use of automatic differentiation to optimize millions of model parameters with a flexible physical model is described for starlight subtraction from real, on-sky coronagraphic images to greatly improve sensitivity.