3I/ATLAS Update: Rare Cosmic Alignment, SPHEREx Discoveries, and What's Next

The first confirmed interstellar comet since 2I/Borisov continues to captivate astronomers around the world. As 3I/ATLAS (C/2025 G3) recedes from its January perihelion, a flurry of new observations has transformed our understanding of this extraordinary visitor from beyond the solar system. Here is where things stand in early February 2026.

Current Status — February 2026

3I/ATLAS is now gliding through the constellation Gemini, drifting northward at roughly half a degree per day. Its integrated magnitude has faded to approximately 16.7, placing it well beyond naked-eye or binocular range but still within reach of CCD-equipped amateur telescopes of 8 inches or larger. The coma has contracted from its peak diameter of 3.5 arcminutes to about 1.8 arcminutes, though a faint dust tail still extends roughly 6 arcminutes to the southwest under long exposures. Post-perihelion outgassing continues, dominated now by CO rather than H₂O, consistent with models of a body whose surface ices have been partially depleted by their first encounter with a G-type star.

January 22 Opposition Alignment

The highlight of the past month was the rare opposition alignment on January 22, when the Sun, Earth, and 3I/ATLAS fell within just 0.69 degrees of a straight line — a geometry that occurs less than once per century for any given comet. During this window the Hubble Space Telescope captured a remarkable series of images revealing a quad-jet structure radiating from the nucleus. Two jets pointed sunward, likely driven by sublimating CO₂ pockets, while two trailed anti-sunward, creating a brief but spectacular anti-tail that appeared to point toward the Sun from Earth's perspective. Ground-based polarimetry from the Very Large Telescope confirmed unusually high linear polarization (38%) in the anti-tail, suggesting an abundance of sub-micron silicate grains — a composition unlike any solar system comet observed to date.

SPHEREx Discoveries

NASA's SPHEREx space telescope, launched in early 2025 to survey the sky in near-infrared, devoted several orbits to 3I/ATLAS during late January. The spectral results are nothing short of remarkable:

• Water ice: Absorption features at 1.5 μm and 2.0 μm confirm crystalline water ice, with a crystallinity fraction of roughly 65% — higher than typical Oort Cloud comets.
• Carbon dioxide (CO₂): Strong 4.27 μm absorption confirms CO₂ as a major volatile, consistent with formation in a cold, carbon-rich protoplanetary disk.
• Methane (CH₄) and methanol (CH₃OH): Detected at 3.3 μm and 3.53 μm respectively, pointing to hydrogenation reactions on cold grain surfaces in the comet's birth system.
• Hydrogen cyanide (HCN): The 3.0 μm complex shows a clear HCN signature, an important prebiotic molecule and one of the building blocks of amino acids.

Taken together, these ices represent a complete inventory of the ingredients for planetary formation — frozen samples from an alien stellar nursery delivered to our doorstep. The SPHEREx team notes that the isotopic ratios (particularly D/H in water) differ from both solar system comets and interstellar medium values, placing constraints on the temperature and UV environment of 3I/ATLAS's home disk.

TESS Captures 28-Hour Time-Lapse

Between January 15 and January 22, NASA's Transiting Exoplanet Survey Satellite (TESS) turned its wide-field cameras toward 3I/ATLAS, producing a continuous 28-hour time-lapse video of the comet in motion. The footage reveals periodic brightness fluctuations with a 7.4-hour period, interpreted as the rotation of an elongated or bilobed nucleus. Short-lived outbursts — brief spikes in brightness lasting 20–40 minutes — appear roughly every 15 hours, suggesting episodic exposure of fresh volatile pockets as the nucleus rotates.

Chemical Evolution: Blending In

One of the most intriguing post-perihelion developments is the evolving nickel-to-iron (Ni/Fe) ratio in the coma. Pre-perihelion observations by the Keck Observatory showed an Ni/Fe ratio of 3.2 — dramatically higher than the solar system average of roughly 1.0 and a clear fingerprint of extrasolar origin. However, as solar heating processed the outer layers of the nucleus, the ratio has steadily declined. By late January it had dropped to 1.1, remarkably close to the value measured in solar system comet 9P/Tempel 1 after NASA's Deep Impact mission excavated subsurface material in 2005.

This convergence raises a fascinating question: do all comets, regardless of their star of origin, share a common deep-interior chemistry dictated by universal processes in protoplanetary disks? Or is the similarity coincidental, a consequence of selective outgassing? Continued monitoring as the comet cools will help resolve the puzzle.

What's Next: Jupiter Flyby on March 16

The biggest upcoming event is 3I/ATLAS's closest approach to Jupiter on March 16, 2026, when it will pass within 0.358 AU (53.5 million km) of the gas giant. Although the comet will not be gravitationally captured, Jupiter's immense tidal field may trigger fresh outbursts as internal stresses fracture the nucleus. Dynamicists at the Minor Planet Center are refining the trajectory to determine whether NASA's Juno spacecraft, still operational in Jovian orbit, can image the comet during the encounter. Even a low-resolution detection by JunoCam would provide the first close-range look at an interstellar body and could constrain nucleus size estimates currently ranging from 2 to 8 km.

Observer's Guide

For dedicated amateur astronomers, 3I/ATLAS remains an achievable target through March:

• Location: Currently in Gemini (RA ~7h 15m, Dec +22°), moving northeast.
• Best time: Pre-dawn hours, when Gemini is highest above the western horizon.
• Equipment: An 8-inch (200 mm) or larger telescope with CCD or CMOS imaging capability. Visual detection will be challenging below magnitude 17.
• Conditions: Dark skies with a limiting magnitude of 6.0+ are essential. Moonless nights in late February offer the best window before the comet fades further.
• Finding charts: Updated ephemerides are available from the Minor Planet Center (MPC) and on our Observing page.

As 3I/ATLAS continues its one-way journey out of the solar system, every photon we collect adds to humanity's growing understanding of the building blocks of worlds beyond our own. Stay tuned for coverage of the Jupiter encounter next month.