Recent telemetry from NASA’s SPHEREx initiative indicates a profound behavioral metamorphosis in the interstellar body 3I/ATLAS, exhibiting characteristics of a fully active comet following a proximate solar transit.
The SPHEREx 0.75-5.0μm imaging of 3I/ATLAS captured between December 8 and 15, 2025. Image attribution: NASA / arXiv: 2601.06759 / Lisse et al., arXiv: 2601.06759.
The SPHEREx observatory documented 3I/ATLAS from December 8 through 15, 2025, subsequent to its closest astronomical proximity to the Sun, a point termed perihelion.
“During December 2025, SPHEREx reassessed 3I/ATLAS post-perihelion, discerning a significantly more dynamic entity when contrasted with the August 2025 SPHEREx pre-perihelion assessments. This revealed pronounced indications of its evolution into a cometary corpuscle undergoing complete sublimation of its volatile ice content,” stated Dr. Carey Lisse, an astrophysicist affiliated with the Johns Hopkins University Applied Physics Laboratory, in conjunction with his collaborators.
The newly acquired SPHEREx data unveil a coma densely populated with gaseous and particulate matter, exhibiting spectral signatures of cyanide (CN), dihydrogen monoxide (H2O), hydrocarbons (C-H), carbon dioxide (CO2), and carbon monoxide (CO).
“The emergent presence of cyanide and organic signatures suggests that these molecular species are enmeshed within the aqueous phases,” remarked Professor Avi Loeb of Harvard University, who was not a participant in this particular investigation, in a related communication.
Investigators observed a substantial augmentation in water vapor activity. Concurrently, emissions from carbon monoxide experienced a precipitous escalation.
“The spectral feature associated with H2O gas, which was marginally discernible in August, is now 20 times more intense, implying the wholesale sublimation of water,” the research team posited.
“The emitted flux of CO has surged by a factor of 20, indicating that the CO/CO2 abundance ratio has concomitantly risen by fifteenfold.”
The contemporary imagery procured by SPHEREx further illustrates a considerable spatial expansion of the celestial body’s gaseous halo.
“The gas-rich comae identified by SPHEREx were fully resolved, extending outwards from 1 to 3 arcminutes in radius. All except the CN and C-H organic comae presented a markedly spherical morphology relative to the Sun and orbital velocity vectors,” the scientific group noted.
“In contrast, the SPHEREx continuum dust and organic images exhibited a distinctly pear-shaped configuration, with the narrower end oriented sunward.”
“The disparities in these forms suggest that CN and C-H originate from the dust particles, while the H2O, CO2, and CO gases emanate from a symmetrically distributed region centered on the nucleus.”
“No discernible jet or anti-solar tail structures were detected.”
The observed alterations, as documented by SPHEREx, point towards a fundamental recalibration of 3I/ATLAS’s physical state.
“The December 2025 observational findings are congruent with a comet that has attained full cometary activity, including the sublimation of even water ice,” the paper’s authors asserted.
“The chemical constitution now aligns with that of conventional Solar System comets, with ice abundance ratios mirroring typical values encountered in the majority of cometary bodies.”
The researchers attribute this transformative evolution to the object’s traversal through the inner Solar System.
“By December, 3I/ATLAS had resided for 3.5 months within the Solar System’s ice line, triggering activity not only in the highly volatile CO2 and CO ice components but across all cometary constituents,” they explained.
“Consequently, the bulk matrix material of the comet began to evaporate, liberating its entire embedded content.”
“A more comprehensive analysis will be undertaken prior to 3I/ATLAS’s next passage through SPHEREx’s planned observational trajectory in April 2026,” the team concluded.
Their dissertation has been submitted for peer review and publication in the Research Notes of the AAS.
_____
C.M. Lisse et al. 2026. SPHEREx Re-Observation of Interstellar Object 3I/ATLAS in December 2025: Detection of Increased Post-Perihelion Activity, Refractory Coma Dust, and New Coma Gas Species. Research Notes of the AAS, submitted for publication; arXiv: 2601.06759
