Kathrine Frich
The interstellar comet known as 3I/ATLAS has reappeared from behind the sun, giving astronomers a new chance to study the rare visitor as it travels through the inner solar system.
The object, first detected in July, is only the third known interstellar comet ever observed. Its reemergence marks the first opportunity for optical imaging since it became obscured by solar glare during its close pass to the sun in late October.
Interest in 3I/ATLAS has remained high among scientists and amateur astronomers alike, as its unusual behavior and trajectory may offer clues about the composition and evolution of comets that form beyond our solar system.
New optical observations from Arizona
Qicheng Zhang, a postdoctoral researcher at the Lowell Observatory in Arizona, used the facility’s Discovery Telescope to capture what is believed to be the first post-perihelion optical image of 3I/ATLAS on October 31.
Zhang also recorded additional images using a small six-inch telescope and shared them on his Cometary blog on November 2.
According to Zhang, the comet should now be detectable with standard amateur telescopes across much of the Northern Hemisphere.
He explained that observers need clear skies and a low eastern horizon, noting that the comet “won’t look very impressive” but should appear as a faint, gradually brightening smudge over the coming days.
Tracking the comet’s journey
Since its discovery, researchers have determined that 3I/ATLAS is moving at more than 130,000 miles per hour (210,000 kilometers per hour) along an unusually flat and straight path.
The comet reached its closest approach to the sun, or perihelion, on October 29, when it came within about 130 million miles (210 million kilometers) of the star.
During this time, astronomers lost direct sight of it from Earth, but continued to monitor its progress through space telescope data.
A recent study by Zhang and a colleague, posted to the preprint server arXiv, suggested that 3I/ATLAS brightened rapidly near perihelion and appeared distinctly bluer than the sun, likely due to gas emissions increasing its visible brightness.
Further observations are needed to determine whether this brightening continues.
Observing challenges and early results
The Lowell Discovery Telescope is one of the few large telescopes capable of viewing the comet so close to the horizon shortly after perihelion.
Zhang reported that he captured his successful image when 3I/ATLAS was roughly 16 degrees away from the sun, just above the horizon during morning twilight.
While there have been radio observations of the comet throughout this period, Zhang said he has not yet seen other confirmed optical detections since it passed behind the sun.
A rare interstellar visitor
Comets typically heat up and release gas as they approach stars, revealing clues about their chemical composition.
Scientists expect to learn much more about 3I/ATLAS in the coming weeks as it moves away from the sun and becomes easier to observe.
Some early research suggests the comet may be billions of years older than our solar system. Its surface, likely altered by long exposure to cosmic radiation, could carry materials from its original star system.
Despite some public speculation about artificial origins, astronomers agree that 3I/ATLAS is a natural interstellar comet, not a spacecraft.
“The comet is rapidly rising from the sun,” Zhang said. “In one week it will be about 25 or 30 degrees away from the sun, allowing larger telescopes around the world to begin tracking it.”
Sources: Live Science, Lowell Observatory, arXiv (Oct–Nov 2025).
This article is made and published by Kathrine Frich, who may have used AI in the preparation
