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Giant exoplanet emerges from the dark when the James Webb Space Telescope turns out the starlight
"We showed that we can actually recover a planet that people previously couldn’t see."
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Sometimes science can seem really counter-intuitive. For example, occasionally in astronomy, you can see more with less light. Case in point: the emergence of a giant planet in observations made by the James Webb Space Telescope (JWST), when astronomers found a way to block out light from the planet's parent star.
The extrasolar planet, or exoplanet, in question is 51 Eridani b (51 ERI b), a gas giant with the same mass as around 11 Jupiters that orbits a star located around 97 light-years away. 51 ERI b was discovered back in 2015 by ground-based telescopes, but the planet was missing from observations of the system made by the JWST. That wasn't a failing of the JWST itself; no one is doubting the observing capabilities of the most powerful telescope humanity has ever hoisted into orbit around Earth. Instead, it was a result of starlight from the star 51 ERI A obscuring this intimidatingly massive world.
The brightest planets are 100,000 times fainter than their host stars, meaning spotting them is like observing a firefly hovering around a lighthouse. Even using a tool called a coronagraph to block the star isn't enough to reveal the planet, as that doesn't stop all the starlight.
The only solution to this glaring problem is a computer program to wipe out the starlight. "For the past 20 years, astronomers have tackled this problem by observing a different star and using its image as a reference," Jason Wang of Northwestern University explained in a statement. "Then, they subtract that reference image from the original observation to remove the unwanted glare to reveal faint planets that otherwise might be hidden."
There is a problem with this process, however. Even the most stable telescopes "wobble." For instance, the JWST requires cryocoolers to keep its NIRCam instrument super cold, and those coolers have little motors that can cause the mirrors to vibrate. This movement, however slight, causes a scatter in starlight. The result is enough glare remaining to obscure a planet, but Wang and colleagues developed a new approach to this problem.
The new approach taken by the team is dubbed Physics-based Learning for Imaging Planets (FLIP), and it involves creating a digital "twin" of a telescope. Essentially a virtual replica that simulates how starlight travels through the telescope's mirrors and reaches its detectors.
This twin is then fine-tuned to account for millions of tiny imperfections in the original telescope. The digital twin is then tweaked until it aligns with observations from the actual telescope. Astronomers can then remove the simulated glare from the original image.
To assess the validity of the technique, the researchers took a second look at JWST observations of two star systems with known exoplanets, HIP 65426 and 51 Eridani, and one system, TYC 5899, with no known planets.