Interstellar Comet 3I/ATLAS Reveals Cosmic Origins with NASA’s SPHEREx Mission

A newly observed interstellar comet, 3I/ATLAS, is offering scientists a rare glimpse into the building blocks of other star systems. Observations made by NASA’s SPHEREx mission in December 2025, along with data from other telescopes, have revealed the presence of organic molecules and a dramatic increase in the comet’s brightness as it passed close to the Sun.

The comet, discovered in July 2025, is only the third confirmed object to originate from outside our solar system. This makes it a unique opportunity to study material that formed around another star, potentially shedding light on the origins of life and the formation of planetary systems.

Organic Molecules Detected

Researchers detected organic molecules within the comet’s coma – the cloud of gas and dust surrounding the nucleus – including methanol, cyanide, and methane. While these molecules are fundamental to biological processes on Earth, their presence doesn’t necessarily indicate life. They can also be created through non-biological processes.

“These observations by NASA’s SPHEREx show the infrared light emitted by the dust, water, organic molecules, and carbon dioxide contained within comet 3I/ATLAS’s coma,” NASA reported. The detection of these molecules provides valuable information about the chemical composition of the interstellar medium – the space between stars – where new stars and planets are born.

A Delayed Eruption

The comet exhibited a significant increase in brightness approximately two months after its closest approach to the Sun. This phenomenon is typical of comets as they warm up and release gases like water, carbon dioxide, and carbon monoxide into space. This process, called sublimation, occurs when ice transitions directly from a solid to a gas without becoming a liquid.

Interestingly, the peak of activity wasn’t observed at the comet’s closest point to the Sun. Scientists explain that heat takes time to penetrate the outer layers of the comet, meaning that deeper layers of ice only began to sublimate later. Observations in August 2025 showed a relatively simple coma, but by December, the activity had become much stronger and more diverse in composition.

“Comet 3I/ATLAS was full-on erupting into space in December 2025, after its close flyby of the Sun, causing it to significantly brighten. Even water ice was quickly sublimating into gas in interplanetary space,” said Carey Lisse, study lead from Johns Hopkins Applied Physics Laboratory. “And since comets consist of about one-third bulk water ice, it was releasing an abundance of new, carbon-rich material that had remained locked in ice deep below the surface.”

A Crusty Traveler

Scientists believe that 3I/ATLAS likely developed a crust over the course of its long journey through interstellar space, due to exposure to radiation. As the comet approached the Sun, the energy from our star eventually penetrated this crust, heating the pure ice beneath and releasing chemicals that had been shielded for potentially billions of years.

Phil Korngut, a scientist involved with the SPHEREx instrument, explained, “The comet has spent centuries crossing interstellar space and likely formed a crust due to radiation processes.”

Beyond Gas: Rocky Material Ejected

In addition to gases, observations also revealed the ejection of rocky material. The dust particles released were relatively large, meaning they weren’t easily pushed away from the comet’s nucleus by the pressure of sunlight.

SPHEREx’s Unique Perspective

The observations of 3I/ATLAS represent a fortunate opportunity for the SPHEREx mission. Launched in March 2025, SPHEREx is designed to map the entire sky in infrared light, studying the origins of the universe and searching for the building blocks of life. The comet’s arrival shortly after the mission’s launch allowed SPHEREx to gather unprecedented data on an interstellar object.

“Our unique space telescopes are collecting unprecedented data,” said Yoonsoo Bach, a deputy lead on the study. “The presence of an interstellar comet just a few months after launch was a rare scientific opportunity.”

SPHEREx’s ability to observe in 102 different infrared wavelengths allows it to detect a wide range of gases and cosmic materials. The mission completed its first all-sky infrared map in late 2025.

Confirming an Interstellar Origin

3I/ATLAS was initially detected by the ATLAS survey telescope in Chile on July 1, 2025. Scientists quickly determined that the object originated outside our solar system based on its speed and trajectory. Since then, various NASA missions have been tracking the comet to understand its composition and path.

This research is helping scientists study ancient material that may hold clues about the formation of stars and planets. NASA has confirmed that 3I/ATLAS poses no threat to Earth, despite some speculation online. The comet is simply passing through our solar system and will eventually return to the vastness of interstellar space.