A planet that had become invisible in images from the James-Webb Space Telescope has reappeared, without any new observations.
Photographing a planet around another star remains difficult, even with a space telescope as powerful as this one. The reason is simple: the star shines much more brightly than the planet. Its light floods the image and can hide anything located right next to it.
Artist's impression of an exoplanet.
Pixabay
To reduce this interference, James-Webb uses a device that blocks a large portion of the star's light. But this filter is not always enough. Bright traces remain in the images, to the point of making a planet that is nevertheless present in the data disappear.
Astronomers usually try to remove these traces by comparing the image with one of another star. The problem? The telescope moves and deforms very slightly, especially when its temperature changes. The two images therefore never look perfectly alike, and traces of the star's light remain visible.
A team led by Northwestern University has developed a new method to achieve this. Its software, called FLIP, reproduces on a computer the path of light through the telescope. It adjusts this reproduction to account for the instruments' tiny imperfections, then removes the unwanted light from the image.
Specifically, the software seeks to reproduce the star's parasitic light traces as faithfully as possible. It then only needs to subtract those parasitic light traces from the captured image to eliminate them. Once they have been removed, much fainter objects become easier to distinguish.
The researchers tested their method on observations previously recorded by James-Webb. In particular, they recovered 51 Eridani b, a giant planet previously discovered with a ground-based telescope. In these images, taken two years earlier, conventional processing could not reveal it at the wavelength studied.
According to the observations, the new method improved the ability to distinguish faint objects by a factor of between two and fifteen.
The method could also help examine the atmospheres of certain planets. The light being studied is notably absorbed by carbon dioxide, making their detection even more difficult. The researchers now plan to use old observations and are also considering applying this approach to future telescopes capable of searching for Earth-like planets.