07/02/2026
New data from Hubble and Webb just made 3I/ATLAS significantly heavier and chemically stranger than we thought.
Hubble successfully detected the nucleus of 3I/ATLAS using post-perihelion observations from December 2025 to January 2026. After subtracting the glowing coma, the nucleus became visible with an effective diameter of 2.6 kilometers. That makes Atlas about 40 times more massive than 2I/Borisov and at least 20,000 times more massive than 1I/'Oumuamua. This isn't a small icy fragment drifting through space. This is a massive body carrying substantial material across interstellar distances.
Webb's MIRI spectrometer observed Atlas on December 15-16 and December 27, 2025. The spectra show water, carbon dioxide, nickel, and methane. Methane production rates measured at 13.7% and 27% of water production during the two observation periods. That's robust detection. Methane is definitely outgassing from Atlas in significant quantities.
But here's the problem. Methane wasn't detected in August 2025. Webb observed Atlas pre-perihelion in August and found carbon dioxide and carbon monoxide, but no methane. SPHEREx spectrophotometry from the same period also detected no methane signature. Methane only appeared after perihelion, months later than it should have.
This is backwards. Methane is hyper-volatile with a significantly lower sublimation temperature than carbon dioxide or carbon monoxide. When a comet approaches the Sun and heats up, methane ice should sublimate first, followed by CO, then CO2, then water ice as temperatures rise. Atlas did the opposite.
Carbon monoxide appeared first in August 2025 despite being more volatile than methane. Carbon dioxide appeared in massive quantities representing 87% of total mass loss. Water appeared later. Methane appeared last post-perihelion in December 2025, despite being the most volatile of all these molecules. Natural sublimation doesn't work this way.
The delayed methane detection suggests methane is depleted in the outermost layers of Atlas and was only exposed to sunlight close to the Sun or after perihelion. This implies a layered composition with outer surface layers containing CO2 and CO but lacking methane, and methane buried deeper inside protected from early sublimation.
But that creates another puzzle. Carbon monoxide is more volatile than methane. If both were buried under outer layers, CO should have been depleted from the surface just like methane. Yet CO was detected early while methane wasn't. The chemistry doesn't follow natural patterns.
Beyond the nucleus size, Hubble observations revealed asymmetric behavior. Atlas faded more rapidly after perihelion than it brightened before perihelion. This activity asymmetry suggests different processes operating before and after closest approach to the Sun. Natural comets typically show symmetric brightening and fading curves.
On January 22, 2026, when Sun, Earth, and Atlas aligned, scattered light from dust grains displayed a 20% opposition surge with a three-degree width, exactly as predicted. The nucleus light-curve shows temporal variations from the 7.1-hour rotation period detected in previous analysis.
Based on Atlas's size and detection, researchers estimate at least one Atlas-sized interstellar object within 4.5 AU of the Sun at any instant. That's likely conservative since inactive objects would be far harder to detect. Multiple objects resembling Atlas probably passed through undetected even before 1I/'Oumuamua was discovered in 2017.
Atlas is at least 20,000 times more massive than 'Oumuamua. It's releasing methane months later than thermodynamics predicts. It showed asymmetric activity before and after perihelion. The chemical timeline is backwards. The mass is unprecedented. And methane appeared exactly when it shouldn't have.
Natural sublimation follows volatility order. Atlas doesn't. That's the problem.
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