Not a day goes by without the interstellar comet 3I/ATLAS providing a new surprise. As the closest to Earth on December 19thEarth’s largest telescopes are peering tirelessly at this rare visitor, trying to gather as much data as possible before it vanishes forever into cold interstellar space. The latest discoveries in chronological order suggest that 3I/ATLAS is composed of carbonaceous chondrites enriched with metals and water icea combination that spawned episodes of cryovolcanism as the comet approached the Sun, behavior similar to that of objects trans-Neptunians of our Solar System. Furthermore its period of 16 hour brightness variationpreviously associated with its elongated shape, could also be generated by a “swarm” of fragments which orbits the comet, as recently suggested by Avi Loeb. Finally, new observations with the James Webb Space Telescope show how the cometary surface shows the effects of billions of years of exposure to cosmic rayswhich changed its composition compared to the original one. In short, 3I/ATLAS remains a scientific puzzle whose pieces we are still trying to put together.
Signs of cryovolcanism and trans-Neptunian chemical composition
Photometric and spectroscopic observations from 3I/ATLAS show a striking similarity to the pristine carbonaceous chondrites from NASA’s Antarctic collection. It would therefore be a question of primitive materialsrich in carbon and native metals such as iron and nickel. Scientists, comparing these samples with the comet’s spectra, found a strong match with the trans-Neptunian bodies (TNO), i.e. the objects that populate the outermost and icy regions of the Solar System. According to scientists, 3I/ATLAS would therefore be a “primordial” object which never passed close to its parent star, was never heated or thermally transformed. This means that under its crust reprocessed by cosmic rays it preserves primordial materiala sort of time capsule of the chemistry of the protoplanetary disk from which it was born.
The study was led by the astronomer Josep M. Trigo-Rodríguez who used telescope images Joan Oró in Catalonia to show how jets of dust and gas rose from the comet’s surface as it approached the Sun, a clear sign of cryovolcanismi.e. eruptions of ice on the cometary surface. This behavior is typical of icy worlds in the outer Solar System which have enough internal heat to melt some of the ice, producing plumes and geysers. In the case of 3I/ATLAS, the process may have been triggered by sublimation of thesolid carbon dioxidewhich allowed theinternal oxidizing liquids to react with reactive metals present in the comet to create an activity similar to “ice volcanoes”produced by a containing body abundant water ice, native metals and “primordial” carbon-based materials.
If this interpretation is confirmed, it will mean that the comet, despite coming from another star system, it bears a striking resemblance to icy objects in our cosmic neighborhood. Furthermore, this would show how carbon-based materials, fundamental to prebiotic chemistry on Earth, may also have come to us from other star systems.
3I/ATLAS is very ancient: it has been exposed to cosmic rays for billions of years
Simulations and observations from the James Webb Space Telescope have shown that 3I/ATLAS has a thick irradiated crustdeeply altered by billions of years of bombardment by galactic cosmic rays. If in the Solar System the heliosphere protects the Earth and other bodies from most of these high-energy rays, in interstellar space this protection does not exist. As a result, the comet absorbed so many galactic cosmic rays during its interstellar journey through the Milky Way that it developed a deep irradiated crust which no longer resembles the material of its star system of origin. These cosmic rays have interacted with carbon monoxide present in cometary ice transforming it into carbon dioxidea, which would explain its observed anomalous abundance. This modification appears to have significantly altered the physical state of the ice of comet 3I/ATLAS, up to a depth of approximately 15-20 meters. What we see externally of 3I/ATLAS is therefore not its primordial version, representative of the environment in which it was formed, but rather a version heavily altered by the bombardment of cosmic rays lasting billions of years.
Is 3I/ATLAS a swarm of objects?
It has been known since July that comet 3I/ATLAS It varies in brightness by 0.3 magnitudes with a period of about 16 hours. Initially this oscillation was interpreted as the signal of a body elongated rotating. But new images ofanti-tail pointing towards the Sun and a drop-shaped glow led physicist Avi Loeb to propose an alternative and much more extreme hypothesis, namely that 3I/ATLAS may not be a single object, but a “swarm” of debrisa group of fragments traveling together, held together by a weak force of gravity. According to this interpretation, what Avi Loeb defines as a “luminous heartbeat” would be the rate at which the cloud of debris rotates in space. This is an interpretation yet to be verified but may be compatible with some irregularities observed in the light of the comet’s coma.
