Webb Studies Keep Saturn-Mass S1 Plausible After 2 Non-Detections at Alpha Centauri A
Updated
Updated · spacedaily.com · Aug 16
Webb Studies Keep Saturn-Mass S1 Plausible After 2 Non-Detections at Alpha Centauri A
2 articles · Updated · spacedaily.com · Aug 16
Summary
Two Astrophysical Journal Letters papers argue S1 could still be a planet around Alpha Centauri A, even though Webb saw the mid-infrared source once in August 2024 and failed to recover it in February and April 2025.
Millions of simulated orbits showed a 52% chance that, if S1 is the same object as the 2019 NEAR candidate C1, orbital motion would have carried it into Webb’s low-sensitivity regions during both follow-up visits.
The original signal was faint—more than 10,000 times dimmer than Alpha Centauri A—with a reported significance of about 3.3 to 4.3 sigma after tests against asteroids, background objects and image-processing artifacts.
Model-dependent estimates place S1 at roughly 90 to 150 Earth masses, near 225 kelvin, on a 2-to-3-year orbit spanning about 1 to 2 AU, making it a temperate gas giant rather than an Earth-like world.
The papers stop short of confirmation: future Webb observations must recover the source at predicted positions, while added filters, astrometry and radial-velocity work could distinguish a real planet from dust or a transient artifact.