The third confirmed visitor from outside our solar system continues to baffle astronomers. Comet 3I/ATLAS reached its perihelion – its closest point to the Sun – around October 29, displaying behavior that again beat scientists’ expectations and revealing clues about its ancient interstellar journey.
In this new chapter of its journey, what surprised researchers the most was the speed at which the comet brightened as it approached the Sun.
Between mid-September and late October, when 3I/ATLAS approached from twice the Earth-Sun distance to 1.36 AU, its brightness increased much more than expected, showing unusual behavior even for such an exotic object.
Observations show an unprecedented increase in brightness
The comet has remained virtually invisible from Earth for the past month, lying almost directly behind the Sun. However, an ingenious group of astronomers found a way to continue observing it during this critical period.
Qicheng Zhang of the Lowell Observatory and Carl Bottoms of the US Naval Research Laboratory turned to the solar monitoring satellites — STEREO-A, SOHO and GOES-19 — to capture the comet’s spectacular transformation, they report. The universe today.
The result was stunning: According to their calculations, the comet’s brightness increased inversely as the heliocentric distance raised to 7.5 degrees, about twice as fast as a normal comet, according to space media.
“The reason for the rapid increase in brightness of 3I, which greatly exceeds the rate of increase in brightness of most Oort cloud comets at a similar radial distance, remains unclear,” Zhang and Bottoms state in a paper published in the Scientific Publications Repository. arXiv, still awaiting expert review.
By comparison, ordinary comets tend to gradually brighten as they approach the Sun, as heat turns ice into gas. However, this interstellar guest shines about twice as bright as normal, 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 released when heated.
It is interesting that in previous observations, the dust of the comet had a reddish tone. The change to a more bluish color indicates that its surface is undergoing some changes, probably – although this has not yet been confirmed – caused by the release of molecules such as cyanogen or ammonia, responsible for the cooler and brighter tone.
On the other hand, images from the GOES-19 satellite confirmed that the comet is surrounded by a large gas-dust envelope – the so-called coma – which stretches across the sky for several arcminutes.
This is a clear indication that 3I/ATLAS is very active and that the sun’s heat is causing its surface to release material at high rates. At its closest point to the Sun, its brightness reached about magnitude 9, enough to be seen in small telescopes.
The research team considers several possible mechanisms to explain the unusual and rapid increase in brightness. This may be due in part to the speed at which the comet is approaching the Sun, although it may also reflect the characteristics of its internal composition.
This is particularly exciting because if the internal composition of 3I/ATLAS is different from that of comets in the Oort cloud, it could indicate that the planetary system from which it originates also has a different chemical composition.
In addition, astronomers believe that the process of sublimation – the direct transformation of ice into gas – occurs in an unusual way: 3I/ATLAS will continue to emit carbon dioxide even at a relatively close distance from the Sun – about three times the Earth-Sun distance – when water vapor normally predominates. This behavior could alter its heating rate and explain its unexpectedly intense glow.
Cosmic rays changed its surface
Beyond its unusual glow, 3I/ATLAS hides invisible scars: a crust deeply altered by cosmic rays during their billion-year journey across the galaxy.
This is evidenced by another recent study, based on observations by the James Webb Space Telescope and still awaiting peer review, it shows that the comet has accumulated so much interstellar radiation that its outer envelope has been chemically transformed to a depth of 15 to 20 meters.
“It’s very slow, but over billions of years the effect is very strong,” explains Romain Majola from the Royal Belgian Institute of Space Aeronomy. Living science.
According to experts, cosmic rays would turn the carbon monoxide on its surface into carbon dioxide, significantly changing its original composition.
The authors believe that these findings could represent a “paradigm shift” in the study of interstellar objects, since, if confirmed, the comet would no longer display the intact material of its star system, but the product of its long journey.
“We have to be careful and take into account the aging process,” warns Maggiola.
Even so, the hope remains that erosion caused by the Sun’s heat as it passes through perihelion can remove the surface layer and reveal the original materials that will allow us to better understand what these space travelers are made of, and thus infer the conditions of the star systems from which they came.
Closer observations of an interstellar comet
The comet, discovered on July 1 by the ATLAS network in Chile, is now traveling at more than 210,000 km/h – about 68 km per second – on an unusually smooth and straight path.
Some studies suggest that 3I/ATLAS may be one of the oldest comets ever observed, having formed about 3 billion years before the Solar System.
Now that it is emerging from behind the Sun, ground-based observatories will be able to study it in detail throughout November and December. In parallel, ESA’s JUICE mission, which is headed for Jupiter, will observe it from deep space between November 2 and 25, with a closest approach on November 4 at a distance of 64 million kilometers.
As reported IFL science, The full JUICE data won’t be released until February 2026 due to low transmission rates, but could show whether solar erosion has exposed pristine material from the comet’s nucleus.
While scientists continue to be puzzled by its rapid increase in brightness – which may be due to its unique composition, speed or features acquired during interstellar travel – one thing is clear: this third visitor from outside our solar system could provide valuable clues about the formation of star systems and the chemical diversity of space.
Edited by Felipe Espinosa Wang with information from Universe Today, Space.com and Live Science.
