Interstellar Comet 3I/ATLAS: new sun-facing jet, imminent perihelion, and what scientists hope to learn

A rare visitor from another star system is putting on a fresh display. Interstellar comet 3I/ATLAS—only the third confirmed interstellar object—has unveiled a prominent sun-facing jet in recent images, just days before its closest approach to the Sun. The activity ups the scientific stakes as multiple spacecraft and observatories ready to probe its chemistry, dust, and interaction with the solar wind.

3I/ATLAS: where it came from and why it matters

3I/ATLAS (also cataloged as C/2025 N1) was discovered in early July and quickly identified on a hyperbolic, one-time pass through our solar system. That alone makes it invaluable: each interstellar object carries unaltered material from a distant planetary nursery, offering a laboratory for comparing how worlds and comets form across the galaxy. With 3I/ATLAS, researchers get a second true cometary benchmark after 2I/Borisov, following the enigmatic—possibly asteroidal—1I/ʻOumuamua.

Latest development: a powerful jet aimed toward the Sun

The newest telescope views reveal a large jet of gas and dust pointing sunward, a geometry that can occur when sunlight heats an active region on the nucleus whose spin and orientation drive material into a narrow outflow. The jet’s structure and brightness encode clues about the grain sizes and volatile ices involved. A sunward jet can also seed fine dust into the coma, where radiation pressure then reshapes it into curved features—patterns modelers will use to derive the comet’s rotation and the location of active vents.

Perihelion timing and visibility window

3I/ATLAS reaches perihelion in late October (around October 29–30, UTC). As it dives to this turning point, activity typically peaks, making the next several days prime time for spectroscopy and imaging. For ground observers, brightness and sky position remain challenging, but professional facilities in both hemispheres are tracking the coma and tail evolution. Schedules are fluid, and viewing prospects can change quickly with outbursts; if you’re planning backyard attempts, look for updated finder charts from reputable astronomy sources and expect modest binocular-class visibility at best.

Key milestones (subject to refinement)

• Discovery: Early July 2025

• Peak activity window: Late October through early November, centered on perihelion

• Post-perihelion science: Weeks to months of monitoring to watch dust fading and volatile depletion

Spacecraft angles: Mars and Jupiter as opportunistic sentinels

A Mars-orbiting imager recently delivered the closest view yet of the interstellar visitor, capturing the jet-fed coma structure at high resolution. Downstream, the Jupiter environment offers a different probe: if 3I/ATLAS’s outflow intersects magnetic field lines that extend into the Jovian system, instruments there could detect enhanced streams of charged particles and dust, providing an indirect sample of the comet’s exosphere. Even a non-detection helps constrain how far the comet’s influence reaches.

What the chemistry is already telling us

Early ultraviolet observations flagged hydroxyl (OH)—a byproduct of water ice being broken apart by sunlight—when the comet was still far from the Sun. That implies water activity turned on unusually early, with inferred water loss rates on the order of tens of kilograms per second at large distance. As perihelion nears, researchers will compare water-driven activity with other volatiles such as carbon dioxide (CO₂) and carbon monoxide (CO) to map how ices are layered in the nucleus. The ratio of these gases, combined with dust color and grain size distributions, can hint at the birth environment—for example, whether the comet formed in a colder, outer disk around another star.

How 3I/ATLAS compares with 1I and 2I

• 1I/ʻOumuamua (2017): Non-cometary appearance, subtle non-gravitational acceleration; composition remains debated.

• 2I/Borisov (2019): Classic long-tailed comet with abundant volatiles; chemistry broadly similar to solar-system comets, suggesting common building blocks.

• 3I/ATLAS (2025): Exhibits robust, structured activity including a sunward jet and early water signatures; offers a second clear cometary template from beyond the Sun.

This progression matters: with each interstellar object, scientists test whether our solar system’s recipe for comets is typical or exceptional. If 3I/ATLAS shows familiar ratios of water to carbon-bearing ices and similar dust properties, it supports universality. If it diverges—say, by displaying unusual volatile ratios or grain compositions—that would point to different protoplanetary conditions in its home system.

What to watch in the coming days

• Jet evolution: Does the sunward jet persist, split, or fade post-perihelion? Changes reveal spin state and vent dynamics.

• Spectral fingerprints: Tracking water, CO₂, and CO near perihelion will refine production rates and thermal models.

• Solar-wind interaction: Look for reports of ion tails and pickup ions; their shapes encode the interplanetary magnetic field and outgassing rate.

• Nucleus constraints: High-resolution sequences may tighten estimates of the nucleus size and rotation period.

Interstellar 3I/ATLAS is entering its most revealing phase right now. The newly observed sun-facing jet, early-onset water activity, and coordinated campaigns from ground and space together promise a detailed case study of a comet forged around another star. Whatever the verdict—familiar chemistry or surprising outliers—the next week will significantly expand our picture of how planet-forming materials are assembled across the Milky Way.