Astronomer Captures First Optical Image of Interstellar Comet 3I/ATLAS After Perihelion

An interstellar visitor, comet 3I/ATLAS, is visible from Earth again after passing behind the Sun, and astronomers have released what is believed to be the first optical image taken after its perihelion passage.

Recent observations

On Halloween (Oct. 31) Qicheng Zhang, a postdoctoral fellow at Lowell Observatory in Arizona, used the facility's Discovery Telescope to image the comet shortly after it re-emerged. Zhang later demonstrated that the object can be detected with small amateur instruments, posting an example on his Cometary blog on Nov. 2. He told Live Science that standard amateur telescopes should begin picking it up across much of the Northern Hemisphere.

"All you need is a clear sky and a very low eastern horizon," Zhang said. "It won't look very impressive — just a smudge — but it will be an increasingly visible smudge over the next few days."

What we know about 3I/ATLAS

Scientists have been studying 3I/ATLAS since its discovery in July. The object is only the third confirmed interstellar body recorded and is traveling through the solar system at speeds exceeding 130,000 mph (210,000 km/h) along an unusually flat, straight trajectory.

The comet briefly fell out of view as it swung around the Sun, reaching perihelion on Oct. 29 at roughly 1.4 astronomical units — about 130 million miles (210 million kilometers) from the Sun. Observers continued to track it using data from space telescopes while it was obscured by solar glare.

Color, brightness and ongoing study

On Oct. 28, Zhang and a colleague posted a study to the preprint server arXiv reporting that 3I/ATLAS underwent rapid brightening before perihelion and appeared distinctly bluer than the Sun. That bluish color is consistent with gas emissions contributing a large fraction of the visible light near perihelion. Zhang cautioned that the comet might still be brightening; further observations are needed to confirm any continuing trend.

Radio observations were collected during perihelion, and while Zhang believes his is likely the first optical image post-perihelion, he acknowledges another optical detection could exist.

How observers can see it now

The Lowell Discovery Telescope is among the largest instruments that can point sufficiently close to the horizon to image the comet so soon after perihelion. From Earth's perspective the object is moving northward away from the northeastern horizon, creating a morning-twilight observing window: the comet sits just above the horizon while the Sun remains low enough for the sky to be dark enough to see it.

Because time on large telescopes is limited, Zhang uses a small 6-inch telescope to test conditions before scheduled Discovery Telescope windows. He captured his image when the comet was roughly 16 degrees from the Sun (about 5 degrees above the horizon).

Origins and scientific importance

Media speculation has occasionally suggested the object might be an artificial spacecraft, but the astronomical community regards 3I/ATLAS as a conventional comet from an unknown stellar system in the Milky Way. One study proposes it could be among the oldest comets observed — potentially billions of years older than the solar system — while other research suggests prolonged exposure to space radiation may have produced a thick, irradiated crust that masks its original surface properties. That crust could make it harder to trace the comet's birthplace.

As comets warm while moving away from a star, ices sublimate into gas and release material that reveals composition. Astronomers expect an active period of follow-up observations in the coming weeks and months to probe 3I/ATLAS's composition and behavior.

"The comet is rapidly rising from the Sun," Zhang said. "I think in one week it's going to be something like 25 or 30 degrees away from the Sun, by which point many other large telescopes around the world will also be able to follow it up."

Key facts at a glance:

• First optical post-perihelion image reported: Oct. 31 (Lowell Discovery Telescope).
• Perihelion date: Oct. 29 at ~1.4 AU (~130 million miles / 210 million km).
• Speed: >130,000 mph (210,000 km/h).
• Appearance: Blue-tinged, consistent with strong gas emissions near perihelion.
• Visibility: Now detectable with many amateur telescopes in the Northern Hemisphere during morning twilight.

Researchers plan intensified multiwavelength follow-up as 3I/ATLAS moves farther from the Sun and becomes accessible to more observatories worldwide.