Our solar system is currently hosting a visitor from another star, and it’s putting on a spectacular and perplexing show. The interstellar comet, designated 3I/ATLAS, has been observed brightening at a surprisingly rapid pace as it made its closest approach to the sun, leaving scientists searching for an explanation. This unexpected behavior could offer a unique glimpse into the chemical makeup of its distant home system.
3I/ATLAS is a rare guest, being only the third interstellar object ever detected passing through our cosmic neighborhood. It follows in the footsteps of the enigmatic ‘Oumuamua and the first confirmed interstellar comet, 2I/Borisov. The brief presence of these celestial travelers provides an invaluable chance for scientists to study materials from planetary systems far beyond our own.
As comets approach the sun, they are expected to brighten. The sun’s intense radiation causes the ice on their surface to turn directly into gas, a process known as sublimation. This process releases gas and dust, forming the glowing halo (coma) and tail that make comets so recognizable. However, the recent brightening of 3I/ATLAS has been far more dramatic than what is typically seen in comets originating from the Oort Cloud, the icy shell at the edge of our own solar system.
Scientists Qicheng Zhang of Lowell Observatory and Karl Battams of the Naval Research Laboratory have been studying this phenomenon. They suggest a few potential reasons for the comet’s unusual activity. One theory is that the comet’s rapid approach speed is a contributing factor. Another, more exciting possibility is that 3I/ATLAS has a fundamentally different composition, shape, or structure compared to our native comets. If true, this could imply that the planetary system from which it was ejected has a distinct chemical environment.
Another proposed explanation involves the specific types of ice sublimating from the comet’s surface. It’s possible that the sublimation of carbon dioxide initially suppressed the more volatile water ice, leading to a later, more dramatic brightening event.
Because of the sun’s glare, ground-based telescopes will have to wait until mid-to-late November 2025 to get another clear view of the interstellar intruder. Until then, the scientific community will be eagerly anticipating what new secrets this visitor from another star will reveal. The continued observation of 3I/ATLAS promises to deepen our understanding of the vast and diverse universe beyond our solar system.