El comet 3I/ATLAS continues to accumulate observations that break the usual patterns. New data from large telescopes and space platforms point to unusual behavior, both in its morphology as in his chemistry, which makes it a first level objective for the scientific community.
Far from any sensationalism, the results published in recent weeks reinforce the image of a interstellar visitor peculiar but natural, and above all, safe for the Earth. Below, we review the most solid findings and upcoming observations.
What telescopes have observed
On August 24, with 3I/ATLAS about 2,75 AU from the Sun and ~2,6 AU from Earth, the KCWI Spectrograph observed the comet between 0,3425 and 0,55 micrometers. These images show an antitail extending toward the Sun, an unusual structure that challenges the simplest view of cometary tails.
Unlike what is expected for dust ejected and pushed by solar radiation, the white light image does not show a typical queueThe emission profiles also showed asymmetries in solar and antisolar directions, a signature consistent with this antitail.
A puzzling chemistry: nickel without iron
the spectrum of gas column Around 3I/ATLAS, it is notable for its intense nickel emission and the absence of iron lines. In narrowband images, the nickel appears more concentrated in the center than cyanide (CN): emissions extend up to approximately 600 km radius for Ni and ~840 km for CN.
To explain this oddity, the authors suggest that near the core there could be a carbonyl process natural, with the in situ formation of nickel tetracarbonyl, Ni(CO)â‚„, which would concentrate the nickel in regions close to the nucleus and give rise to the observed spectral signature.
Another notable anomaly is that the Ni production rate relative to CN It is larger than that measured in 2I/Borisov and several orders of magnitude larger than the median for comets in the Solar System, reinforcing the atypical nature of 3I/ATLAS within the known cometary family.
Active water far from the Sun
The Neil Gehrels Swift Observatory detected hydroxyl (OH), the characteristic ultraviolet echo of the dissociation of water, when the comet was located at ~2,9 AU. At that distance, activity is usually low, but calculations suggest a water loss of around 40 kg/s, a remarkable figure for an object so far from the Sun.
A plausible explanation is that radiation is heating and evaporating fine grains of ice released by the core, generating a persistent gaseous envelope. Initial observations with the James Webb probe also suggest a high CO₂/H₂O ratio compared to the usual one, which would reinforce the idea of ​​an unusual mixture of volatiles.
Photometric and spectral analyses, on the other hand, draw an object with reddish tone and dust similar to that of the D-type asteroidsEstimates of the nucleus size range from a few hundred meters to several kilometers (up to ~5,6 km), consistent with an active comet.
Its hyperbolic trajectory and its speed, of the order of 210.000 km/h (about 58 km/s), confirm the interstellar origin and fit with the diversity already seen in 'Oumuamua and 2I/Borisov, although 3I/ATLAS is showing a own chemical and dynamic profile.
What's next?
The camera HiRISE, aboard the Mars Reconnaissance Orbiter, captured images on October 2 with a resolution close to 30 km per pixel, about three times better than the best previous images from Keck and Hubble, taking advantage of the move from 3I/ATLAS to ~30 million km from MarsThese side views of the glow will provide clues about the structure of the coma and antitail.
Contributions are planned later from (November) and Juno (March), which will help outline its evolution after the peak of solar activity. The comet will go through a period of low visibility from late September to early December as it moves behind the Sun from Earth's perspective, and will be visible again afterward. At all times, the anniversaries indicate a closest approach to Earth of ~1,8 AU (about 270 million km), without risk scenarios.
With a growing data set and several instruments lined up, 3I/ATLAS is shaping up to be a exceptional natural laboratory: Persistent anti-tail, unusual chemistry and long-distance activity create a portrait that challenges classic patterns and promises answers—and new questions—in the coming months.
