When most people imagine the vastness of space, they picture a dark void with plenty of observable objects. Planets, stars, and other galaxies often come to mind when picturing what space actually looks like. This, however, is a severe understatement of the true emptiness that the universe holds. Imagine your commute to class; maybe it takes you walking across campus, or a few blocks through the city. Maybe you even drive over an hour. If you compared that to an entire trip around the Earth, you’d still only be traveling 1/3735 of the distance from the Earth to the Sun. Comparing that distance to the gap between our solar system and the next, or the Milky Way to all other galaxies, the numbers become incomprehensibly large and unperceivable to humans on Earth.
Since space is made of so much ‘nothing,’ it is no surprise that most objects floating around go undiscovered. Despite Galileo and Sir Isaac Newton beginning their study of the stars in the 1600s, it wouldn’t be until 2017 that humans would discover the first confirmed interstellar objects within the bounds of our own solar system. Aptly named 1I/’Oumuamua, 2I/Borisov, and now 3I/ATLAS are the only recorded objects to have originated from outside of our solar system. Although it is highly theorized that every part of our solar system was impacted by interstellar events — be it original planets with unstable orbits making their exit from the sun, or collisions between planets and asteroids creating moons — technology has only recently become capable of confirming the origin of certain celestial objects via their trajectories.
The main question scientists were asking on July 1, 2025, the day 3I/ATLAS was discovered, was what actually is the object? According to research done via NASA’s Hubble Space Telescope, 3I/ATLAS is a comet with an icy nucleus surrounded by a cloud of dust. Due to difficulties in measuring objects at such speed and distance, the comet has a predicted diameter between 1500 feet and 3.5 miles. Unlike comets from within the solar system, ATLAS is composed of a higher-than-average proportion of carbon dioxide. This chemical makeup could be used to characterize or understand the environment from which the comet originated, and eventually understand the differences between our own solar system and every other type that exists in the universe. While the first sightings of ATLAS occurred in May of this year, NASA’s Transiting Exoplanet Survey Satellite (TESS) was not capable of capturing objects at speeds similar to what the comet was traveling at. Due to this, it took until the completion and launch of NASA’s Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer (SPHEREx) Observatory to fully capture ATLAS.
One of the biggest draws to the study of ATLAS was its close proximity to Earth. While 1.8 astronomical units (or 170 million miles) may seem like a stretch for ‘close proximity,’ this distance allowed for adequate research on the object enough to relate it to the other interstellar visitors. Despite the expected arrival of more comets after ‘Oumuamua, as hinted at by the naming scheme, the three objects have proven to be very different. ‘Oumuamua seemed not to be a comet at first, with a strangely oblong shape and unique tumbling motion through space. While ATLAS and Borisov both more clearly appeared to be comet-like objects, Borisov had a much higher carbon monoxide makeup as opposed to the presence of carbon dioxide in ATLAS. Borisov also appeared to be closer in age to the solar system itself, likely under one billion years old, with ‘Oumuamua closer to two billion years, and ATLAS likely even closer to ten or eleven billion years. These key differences point to totally unique origins and life stories of these objects, which can now further the study of solar systems outside of our own.
3I/ATLAS will continue its trek through the solar system and reach its closest point to the sun — its perihelion — on October 29. The comet will then be observable again in early December and will slowly continue out of the bounds of the sun, continuing its endless path into space. Just like the aftermath of 1I/’Oumuamua and 2I/Borisov, it is inevitable that scientists will spend the coming years awaiting the arrival of 4I, 5I, and so forth. Since the likelihood of detecting interstellar visitors only increases as technology improves, the study of each one will slowly fill in the cosmic jigsaw puzzle that scientists are hoping to complete.
