When the interstellar object named 3I/ATLAS began its descent toward the Sun, ground-based telescopes had to abandon observations due to solar glare. Scientists then turned to space observatories like SOHO and STEREO-A, which captured exceptional images of this rare phenomenon. These specialized instruments made it possible to track the comet's evolution as it passed through the most hostile regions of our solar system.
Observation sequence of the interstellar comet 3I/ATLAS by different space instruments, showing its unusual luminous behavior during its approach to the Sun
Credit: arXiv (2025). DOI: 10.48550/arxiv.2510.25035
What particularly intrigued the scientific community was the intensity and speed with which this object began to shine. While classical comets typically experience a gradual increase in brightness as they warm up, 3I/ATLAS underwent a spectacular amplification in a very short time. Researchers describe in their study published on
arXiv an acceleration of the luminous phenomenon unprecedented in the annals of cometary astronomy.
The unusual blue color emitted by this comet constitutes another mysterious element. Normally, comets appear rather reddish due to sunlight reflected by dust particles. Here, the azure hue suggests particularly intense gas emission, probably due to molecules like carbon monoxide or cyanogen that illuminate under the effect of solar radiation. This color dominance indicates a chemical composition distinct from that of usual comets.
Preliminary analyses reveal that this interstellar visitor has a unique chemical signature, with abnormally high proportions of carbon dioxide and the presence of more volatile ices than those encountered in our solar system. These peculiarities could explain the observed bursts of activity, as these substances transform more easily into gas under the effect of solar heat. The detection of unusual metals adds further to the singularity of this object.
Now that the comet is moving away from the Sun, astronomers are preparing an intensive observation campaign with the largest ground-based telescopes. These new studies should help uncover the secrets of its composition and better understand the fundamental differences between the materials that populate our solar system and those coming from other systems.
Interstellar comets, messengers from other worlds
Interstellar comets like 3I/ATLAS represent unique samples of matter from other planetary systems. Unlike native comets of our solar system that orbit the Sun, these interstellar travelers pass through our cosmic neighborhood before heading back into infinity. Their detection remains exceptional due to their low brightness and high speed.
The hyperbolic trajectory of these objects allows them to be distinguished from local comets. Their speed, too high to be captured by solar gravity, betrays their extrasolar origin. Studying their composition thus offers a direct window into planetary formation processes in other stellar systems, without needing to travel to these distant worlds.
Each detected interstellar object provides valuable information about the chemical diversity of our galaxy. The compositional differences with bodies in the Solar System inform us about the conditions prevailing in protoplanetary disks around other stars. These variations can be explained by different formation temperatures or distinct evolutionary histories.
The rarity of these observations makes each detection particularly significant for astronomers. Technological advances in observation instruments now make it possible to detect increasingly fainter objects, increasing the chances of discovering new interstellar visitors in the coming years.