The third confirmed visitor from outside our solar system continues to baffle astronomers. Comet 3I/ATLAS reached its perihelion – the closest point to the Sun – around October 29, displaying behavior that once again defies scientific expectations and revealing clues about its ancient interstellar journey.
In this new chapter of its journey, what has surprised researchers most is the speed with which the comet has illuminated as it approached the Sun.
Between mid-September and late October, as 3I/ATLAS approached from about twice the Earth-Sun distance to 1.36 astronomical units, its brightness increased much more dramatically than expected, showing atypical behavior even for such an exotic object.
Observations reveal unprecedented brightness increase
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From Earth, the comet has remained virtually invisible for the past month, lying almost directly behind the Sun. However, an ingenious team of astronomers found a way to continue observing it during this critical period.
Qicheng Zhang of Lowell Observatory and Karl Battams of the US Naval Research Laboratory turned to solar monitoring satellites – STEREO-A, SOHO and GOES-19 – to capture the comet’s spectacular transformation, they reported. Universe Today.
The result was astonishing: according to their calculations, according to the space media, the comet’s brightness increased in inverse proportion to the heliocentric distance raised to the 7.5 power, approximately twice as fast in its brightness increase as a typical comet.
“The reason for the rapid brightness increase of 3I, which far exceeds the rate of brightness increase of most Oort cloud comets at a similar radial distance, remains unclear,” Zhang and Battams state in a paper published in the Scientific Prepublications Repository arXiv, still pending peer review.
By comparison, common comets tend to gradually brighten as they approach the Sun, when heat turns ice into gas. However, this interstellar visitor is shining at about twice the usual speed, indicating that something unusual is happening on its surface.
Unique chemical composition
Observations showed that comet 3I/ATLAS shines with a bluish hue, different from the golden reflection of the Sun. This color indicates that its luminosity comes not only from dust, as is often the case in comets, but also from gases that are actively being released as it heats up.
The curious thing is that in previous observations the comet’s dust showed a reddish tone. The change to a more bluish color suggests that its surface is undergoing some change, probably – although still unconfirmed – caused by the release of molecules such as cyanogen or ammonia, responsible for that colder and brighter tone.
On the other hand, images from the GOES-19 satellite confirmed that the comet is surrounded by a large envelope of gas and dust – the so-called coma – that extends several arc minutes in the sky.
This is a clear sign that 3I/ATLAS is very active and that solar heat is causing its surface to release material at high speed. During its closest point to the Sun, its brightness reached approximately magnitude 9, enough to be visible with small telescopes.
The team of researchers considers several possible mechanisms to explain the unusual and rapid increase in brightness. It could be related, in part, to the speed at which the comet approaches the Sun, although it could also reflect characteristics of its internal composition.
This is particularly exciting because if the internal composition of 3I/ATLAS differs from that of comets in the Oort cloud, it could suggest that the planetary system it comes from also has a different chemical composition.
In addition, astronomers believe that its sublimation process – the direct conversion of ice into gas – occurs in an unusual way: 3I/ATLAS would continue to expel carbon dioxide even at a relatively close distance to the Sun – about three times the Earth-Sun distance – when water vapor would normally predominate. That behavior could have altered its heating rate and explained its unexpectedly intense glow.
Cosmic rays transformed its surface
Beyond its unusual luminous behavior, 3I/ATLAS hides invisible scars: a crust deeply altered by cosmic rays during their billion-year journey through the galaxy.
This is suggested by another recent study, based on observations from the James Webb Space Telescope and still awaiting peer review, it indicates that the comet has accumulated such an amount of interstellar radiation that its outer shell has been chemically transformed to a depth of between 15 and 20 meters.
“It is very slow, but over billions of years, the effect is very strong,” explains Romain Maggiolo, from the Royal Belgian Institute of Space Aeronomy, Live Science.
According to experts, cosmic rays would have converted the carbon monoxide on its surface into carbon dioxide, significantly altering its original composition.
The authors consider that these findings could represent a “paradigm change” in the study of interstellar objects, since, if confirmed, the comet would no longer show the pristine material of its star system of origin, but would be a product of its long journey.
“We have to be careful and take into account the aging processes,” warns Maggiolo.
Even so, there remains hope that the erosion caused by solar heat during its passage through perihelion can remove the surface layer and reveal original materials, which would allow us to better understand what these cosmic travelers are made of and, with this, infer the conditions of the star systems from which they come.
Upcoming observations of the interstellar comet
Discovered on July 1 by the ATLAS network in Chile, the comet is now traveling at more than 210,000 km/h – about 68 km per second – following an unusually flat and straight path.
Some studies suggest that 3I/ATLAS could be one of the oldest comets ever observed, formed about 3 billion years before the solar system.
Now that it emerges from behind the Sun, ground-based observatories will be able to study it in detail during November and December. In parallel, ESA’s JUICE mission, heading to Jupiter, will observe it from deep space between November 2 and 25, with a maximum approach on November 4, at 64 million kilometers.
As reported IFL Science, The full JUICE data will not be published until February 2026, due to low transmission rates, but could reveal whether solar erosion has exposed pristine material from the comet’s core.
While scientists continue to be baffled by its rapid increase in brightness – which could be due to its unique composition, its speed or quirks acquired during its interstellar journey – one thing is clear: this third visitor from beyond our solar system could offer valuable clues about the formation of star systems and the chemical diversity of the cosmos.
Edited by Felipe Espinosa Wang with information from Universe Today, Space.com and Live Science.
