3I/ATLAS Jets: How an Interstellar Comet's Outgassing Revealed Alien Chemistry

When Comet 3I/ATLAS swept through our solar system in 2025, it didn't arrive quietly. As the Sun's heat reached its ancient interstellar ices, the comet erupted with spectacular jets of gas and dust — giving astronomers an unprecedented window into the composition of material from another star system.

These cometary jets have become one of the most scientifically valuable aspects of 3I/ATLAS. Here's what they've revealed about this extraordinary interstellar visitor.

What Are Cometary Jets?

Cometary jets form when solar radiation heats a comet's surface, causing volatile ices beneath the crust to sublimate — transforming directly from solid ice into gas. This gas erupts through cracks and vents in the nucleus, carrying dust particles with it and creating focused streams of material that can extend thousands of kilometers into space.

For most solar system comets, these jets are powered primarily by water ice. But 3I/ATLAS proved to be different from the very beginning, and its jets told a story of alien chemistry.

JWST Reveals an Alien Composition

In August 2025, the James Webb Space Telescope turned its powerful infrared instruments toward 3I/ATLAS and made a startling discovery: the comet's outgassing was dominated by carbon dioxide (CO₂), not water.

This was immediately significant. Solar system comets are overwhelmingly water-driven — H₂O typically accounts for 80% or more of their volatile emissions. But JWST's spectroscopy showed that 3I/ATLAS was CO₂-rich, with additional detections of:

• Water ice and vapor — present but not dominant
• Carbon monoxide (CO) — a common cometary volatile
• Carbonyl sulfide (OCS) — a sulfur-bearing molecule rarely detected in comets
• Hydrogen cyanide (HCN) — a prebiotic molecule that plays a role in the chemistry of life

This composition fingerprint tells us that 3I/ATLAS formed in a cold, CO₂-rich environment around its parent star — likely farther from its star than where most of our solar system's comets formed. It's essentially a frozen sample from an alien protoplanetary disk, preserved for billions of years in the deep freeze of interstellar space.

The Wobbling Jets: A Spinning Nucleus

One of the most intriguing observations came from ground-based telescopes studying the spatial distribution of 3I/ATLAS's outgassing. Astronomers at the Keck Observatory and the Institute for Astronomy (IfA) in Hawaii found that the comet's cyanide (CN) emissions weren't uniformly distributed around the coma — instead, they appeared concentrated in two distinct jets.

These jets exhibited a characteristic wobbling pattern, creating a helical or corkscrew-like structure as the nucleus rotated. This is a telltale signature of a spinning comet with active vents on specific regions of its surface. As the nucleus rotates, the jets sweep through space like a cosmic lawn sprinkler.

The wobbling behavior told astronomers several things:

• The nucleus is actively rotating, with a measurable spin period
• Active regions are localized — not the entire surface is outgassing equally
• The jet geometry is asymmetric, suggesting an irregularly shaped nucleus with distinct active zones

Observations by Keck and VLT also detected emissions of nickel (Ni) and cyanide (CN) at remarkable rates — nickel was being released at approximately 4.6 grams per second, while cyanide emission reached 17.6 grams per second during the August 2025 peak.

Post-Perihelion: The Jets Intensify

After 3I/ATLAS reached perihelion (its closest approach to the Sun at 1.36 AU) on October 24, 2025, observers expected the jets to gradually fade as the comet moved away from the Sun. Instead, the post-perihelion period brought some of the most dramatic activity yet.

By November 8, 2025, astrophotographers and professional observers documented multiple distinct jets emanating from the nucleus, accompanied by a bright halo of gas and dust extending approximately 500,000 kilometers into space — roughly 1.3 times the distance from the Earth to the Moon.

This extended halo was visible in both broadband imaging and narrowband filters targeting specific molecular emissions. The fact that 3I/ATLAS remained so active well after perihelion suggests that the solar heating had penetrated deep into the nucleus, continuing to liberate volatile ices even as the comet receded from the Sun.

What Makes 3I/ATLAS's Jets Different?

Compared to the jets of solar system comets, 3I/ATLAS's outgassing stands out in several ways:

Feature	Solar System Comets	3I/ATLAS
Primary volatile	Water (H₂O)	Carbon dioxide (CO₂)
Jet structure	Often single dominant jet	Multiple asymmetric jets
Nickel emission	Rarely detected	4.6 g/s at peak
OCS detection	Very rare	Confirmed by JWST
Post-perihelion activity	Typically fading	Intensified with extended halo

The CO₂-dominated composition is particularly telling. In our solar system, CO₂-rich comets tend to originate from the outer Oort Cloud or were formed beyond the CO₂ snow line. For 3I/ATLAS, this composition suggests it formed in the equivalent cold outer regions of its home planetary system — a place where CO₂ could freeze but water may have been less abundant or already depleted.

The Anti-Tail: Jets Facing the Sun

Perhaps the most visually striking phenomenon was 3I/ATLAS's anti-tail — a spike of material that appeared to point toward the Sun rather than away from it. While anti-tails are an optical illusion caused by viewing geometry (we see dust left behind in the comet's orbital plane projected against the sky), the wobbling jets contributed real material to this feature.

Space.com reported that the "weird wobbling jets" were observed in the comet's sun-facing direction, creating an unusual forward-scattered appearance. This anti-tail became one of the most photographed features of 3I/ATLAS during its peak visibility period.

Why the Jets Matter for Science

The jets of 3I/ATLAS represent something remarkable: they are direct samples of material from another star system, liberated from billions of years of cold storage by our Sun's warmth. Every molecule detected in these jets — every grain of dust, every wisp of gas — carries information about:

• The chemistry of the alien protoplanetary disk where 3I/ATLAS formed
• The temperature and pressure conditions in that distant nursery
• The building blocks available for planet formation around other stars
• Whether prebiotic chemistry (molecules like HCN that are precursors to life) is common across the galaxy

As astronomers continue analyzing the data gathered during 3I/ATLAS's passage, the jets will remain a central focus. They transformed what could have been a brief sighting of a distant dot into a rich, multi-wavelength study of alien material — one of the most valuable datasets in the history of cometary science.

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Explore the full journey of 3I/ATLAS through our solar system on the interactive orbit tracker, and follow the complete timeline of discoveries and observations.