Nickel is detected in an interstellar comet, confusing NASA scientists

Astronomers have spotted nickel gas streaming from comet 3I/ATLAS, an interstellar object, a body from outside our solar system, while it was still far from the Sun.

In a new study, researchers used the Very Large Telescope in Chile to catch the signal earlier than ever for an interstellar visitor.

The same campaign confirmed something else unusual. NASA’s Webb telescope found that the comet’s gas cloud is unusually rich in carbon dioxide compared with water, a chemical profile rarely seen so far from the Sun.

That combination raises fresh questions about how a comet can release metal atoms in such cold conditions.

How nickel got into this comet

The work was led by Rohan Rahatgaonkar, a doctoral researcher, at the Institute of Astrophysics of Pontificia Universidad Católica de Chile (PUCC). His research focuses on comet chemistry and interstellar visitors.

Nickel atoms usually hide inside tough minerals that require high temperatures to vaporize. Detecting free nickel out where sunlight is weak suggests a gentler release route that can operate in the cold.

One possibility involves photodissociation, light driven breakup of molecules, that frees nickel from fragile carriers as sunlight hits dust grains.

Another possibility is low temperature chemical processing on grain surfaces that primes nickel for easy escape.

What the telescopes saw

The team first detected multiple nickel lines in late July when the comet was nearly four times farther from the Sun than Earth.

Weeks later they recorded cyanogen, or cyanogen, a simple carbon nitrogen molecule seen as the CN band in many comets, as the comet brightened.

Their measurements show nickel production growing rapidly as the comet moved inward, while iron stayed below the detection limit. That mismatch hints at a nickel specific carrier that breaks apart more readily than iron based ones.

Webb’s Near Infrared Spectrograph found an extraordinary CO2 to H2O ratio, about eight to one, in the comet’s coma, the diffuse gas and dust shroud surrounding a comet’s nucleus.

The paper reports CO2, water vapor, carbon monoxide, and water ice grains, a mix that is more typical closer to the Sun.

3I/ATLAS swung through its perihelion, closest approach to the Sun, near 130 million miles from the Sun. NASA notes that the comet stayed far from Earth throughout its pass.

Uncommon chemistry

If iron is absent while nickel is present, the source is unlikely to be hot sublimation of metal rich dust. The data point toward low activation energy processes that start working at modest surface temperatures.

One candidate is a metal carbonyl, a volatile metal plus carbon monoxide complex that breaks apart easily under light.

Nickel tetracarbonyl is especially volatile, so a small reservoir trapped in or on dust could release nickel atoms when warmed slightly.

Another route could be photon stimulated desorption, where UV light flicks atoms out of surface sites.

That fits the steep increase of nickel with decreasing heliocentric distance, distance from the Sun, because the illumination rises and near surface chemistry speeds up.

These mechanisms also match the timing. The team saw nickel well before classic water driven activity dominated, which argues for carriers that activate early in the inbound leg.

Clues from other comets

Earlier research showed that iron and nickel atoms appear in many solar system comets, even far from the Sun. Heavy metal lines turned up in cold comae where metals were not expected to vaporize.

For the previous interstellar visitor, a report documented atomic nickel in 2I/Borisov’s coma at similar distances. That parallel suggests that low temperature metal release might be common beyond our system.

Normally, there is about ten times more iron than nickel in comets, but researchers noted nearly equal amounts of both elements. That imbalance helps explain why detecting nickel without iron is so striking.

Taken together, these comparisons help separate effects of observation from genuine chemistry. They show a pattern where nickel can appear early, before stronger water activity takes over closer to the Sun.

What it means for planetary systems

Comets lock away the raw stuff of planets in ices and dust. When one from another star system wakes up here, it brings a chemical fingerprint of its birthplace.

The CO2 heavy coma hints that 3I/ATLAS formed or stored ice where carbon dioxide freezes efficiently. That environment may expose metals and organics to radiation that sets up low temperature release pathways later.

Nickel without iron invites a rethink of how metals travel in comae. Weakly bound organometallic carriers, or fragile nanophases, could be widespread, shaping the earliest steps of metal chemistry around young stars.

Future observations should track whether nickel flux rises and falls with carbon monoxide or carbon dioxide. A tight correlation would support low temperature carriers over hot dust evaporation.

Testing these ideas

High resolution spectra can map the spatial profile of nickel lines relative to gas jets. A nucleus centered spike would point to short lived parents that break near their source.

Deep infrared scans could hunt for faint signatures of suspected carriers. Even non detections would set useful limits on those fragile molecules.

Coordinated monitoring across instruments matters. The VLT’s optical spectrograph, a device that spreads light into fine wavelengths, complements Webb’s infrared view to link metals with the driver gases.

As 3I/ATLAS fades, modeling can test which energy barriers fit the observed rise in nickel. That will tell us whether sunlight alone explains the chemistry or if extra triggers are needed.

Nickel in comet 3I/ATLAS

Nickel atoms are not just curiosities. They are tracers of specific chemical pathways that unlock metals at low temperatures.

Seeing them this far out opens a window into reactions that textbooks often treat as niche. It shows that gentle processes can leave sharp signatures across millions of miles.

For planetary science, interstellar comets are natural probes. Each one samples a different disk, adding points to a map of how planets take shape around other stars.

That is why this detection matters. It challenges comfortable assumptions and gives chemists and astronomers a shared target for the next round of tests.

The study is published in The Astrophysical Journal Letters.

Image credit: NASA/ESA/David Jewitt (UCLA)/ Image Processing: Joseph DePasquale (STScI).

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