January 20, 2026 — The third known interstellar object to visit our solar system, 3I/ATLAS, has undergone a remarkable transformation. New observations from NASA's SPHEREx mission show the once-quiet visitor has developed all the classic signs of a fully active comet following its close pass by the Sun in late October 2025. The latest findings, published yesterday (January 19, 2026) on Sci.News and based on a freshly submitted scientific paper, reveal surging water ice sublimation and a rich gaseous coma — marking a dramatic shift from its pre-perihelion state.
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| The SPHEREx 0.75-5.0μm imaging of 3I/ATLAS taken on December 8 to 15, 2025. Image credit: NASA / arXiv: 2601.06759 / Lisse et al., arXiv: 2601.06759. |
A Dramatic Post-Perihelion Transformation
Discovered in July 2025 by the ATLAS survey, 3I/ATLAS quickly earned its "interstellar" designation due to its hyperbolic orbit — confirming it originated from outside our solar system. Like its predecessors 1I/'Oumuamua and 2I/Borisov, it offered a rare glimpse into materials from another star system.
SPHEREx, NASA's infrared all-sky survey mission, observed the object both before and after its perihelion (closest approach to the Sun) on October 29-30, 2025. The pre-perihelion data from August 2025 showed modest activity dominated by highly volatile ices like CO and CO₂. But the new December 8-15, 2025 observations paint a very different picture.
According to lead author Dr. Carey Lisse of the Johns Hopkins Applied Physics Laboratory and co-authors: "SPHEREx re-observed 3I/ATLAS post-perihelion, finding a much more active object... with marked evidence for development into a cometary body fully sublimating all its ices."
The coma — the fuzzy envelope of gas and dust — is now rich in multiple species: cyanide (CN), water vapor (H₂O), organic compounds (C-H stretches), carbon dioxide (CO₂), and carbon monoxide (CO). Water emission, barely detectable earlier, is now 20 times stronger, while CO flux has also increased dramatically. The CO/CO₂ ratio has shifted 15-fold.
Distinct Morphologies and What They Reveal
Infrared images show intriguing differences in shape. Most gas comae (H₂O, CO₂, CO) appear nearly spherical and symmetric around the nucleus. In contrast, the dust continuum and organic emissions form a distinct pear-shaped structure, with the narrow end pointing toward the Sun — suggesting larger dust grains influenced by solar gravity rather than radiation pressure.
No obvious jets or anti-solar tails were detected, which the team notes is consistent with a uniformly active nucleus now evaporating its full inventory of ices after spending months inside the solar system's "ice line."
The researchers conclude that 3I/ATLAS now behaves like a typical solar system comet, with ice ratios matching those seen in most known comets. "Bulk matrix comet material was evaporating, releasing everything the comet contains," they write.
Alternative Perspectives and Ongoing Debate
Harvard astronomer Professor Avi Loeb, not involved in the study, commented on the new cyanide and organic features, suggesting they likely reside in water-rich phases. In a recent Medium post, Loeb highlighted what he sees as an anomaly: the pear-shaped dust distribution and the massive dust mass needed to explain the brightness, raising questions about whether interstellar objects might differ fundamentally from familiar comets.
While the primary study interprets the data as natural cometary evolution, the discussion underscores the excitement — and open questions — surrounding these rare visitors. Further SPHEREx observations planned for April 2026 may provide more clarity.
Sources and Further Reading
- Primary scientific paper: SPHEREx Re-Observation of Interstellar Object 3I/ATLAS (arXiv:2601.06759)
- Latest news coverage (January 19, 2026): Sci.News – 3I/ATLAS Shows Signs of Full Cometary Awakening after Perihelion
- Avi Loeb's commentary on potential anomalies: SPHEREx Images and a New Anomaly Regarding the Gas Plume Around 3I/ATLAS
- NASA SPHEREx mission overview: spherex.caltech.edu
Оригинальная статья: Interstellar Comet 3I/ATLAS Awakens Fully After Perihelion on Planet Today 🚀
Автоматически переопубликовано из основного блога.
