A NASA spacecraft that observes the Universe in infrared has given scientists brand new information about comet 3I/ATLAS.
Discoveries at the comet include the presence of organic molecules, a dramatic change in its brightness and the detection of debris flowing from the interstellar body out into space.
More on 3I/ATLAS
The molecules discovered at 3I/ATLAS can be the foundation for biological processes on Earth, but scientists say they may be produced by non-biological processes too.
Our final observations of 3I/ATLAS?
We're approaching the final period of our ability to observe comet 3I/ATLAS up close.
The comet was discovered on 1 July 2025 and since then has been passing through our Solar System.
It's an interstellar body, which means it originated beyond our Solar System, in a different part of the Galaxy.
3I/ATLAS is one of only three such interstellar bodies ever discovered.
Since its discovery, it has made close passes of the Sun and Earth, it's been photographed by humanity's best telescopes, by spacecraft at Mars and missions on their way to Jupiter.
SPHEREx meets the interstellar visitor
The latest trove of data on 3I/ATLAS comes courtesy of a NASA spacecraft that scans the sky in near-infrared light.
SPHEREx s designed to give astronomers greater insight into objects in deep space like stars and galaxies, but it's been pointed at the interstellar comet to see what it can pick up.
These December 2025 observations follow previous SPHEREx observations of 3I/ATLAS in August 2025.
In these new observations, scientists say they've detected organic molecules like methanol, cyanide and methane.
On Earth, organic molecules like these are a sign of biological processes occurring, but they can be produced by non-biological processes, too.
SPHEREx also found a sharp increase in brightness that occurred two months after the comet made its close approach to the Sun.
This is a common trait of comets that pass close to our Sun, as solar energy causes these frozen, icy space rocks to vent water, carbon dioxide and carbon monoxide into space.
"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," says study lead Carey Lisse of Johns Hopkins Applied Physics Laboratory in Laurel, Maryland.
"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.
"We are now seeing the usual range of early Solar System materials, including organic molecules, soot and rock dust, that are typically emitted by a comet."
3I/ATLAS is venting material into our Solar System
The delay between the comet's close approach to our Sun and the venting of material into space, say scientists, is a result of the time it takes heat from the Sun to travel down into the depths of the comet.
This venting produces a 'coma' around the head of the comet, and this too is a common trait of comets that pass close to the Sun
SPHEREx analysis of the coma revealed huge amounts of carbon dioxide, a little carbon monoxide and some water during the August 2025 observations.
The December 2025 observations show a more active, diverse coma, scientists say, generated by subsurface water ice mixed with other ices, organics and rocky material.
"The comet has spent ages traversing interstellar space, being bombarded by highly energetic cosmic rays, and has likely formed a crust that’s been processed by that radiation," says Phil Korngut, the mission’s instrument scientist at Caltech in Pasadena, California.
"But now that the Sun’s energy has had time to penetrate deep into the comet, the pristine ices below the surface are warming up and erupting, releasing a cocktail of chemicals that haven’t been exposed to space for billions of years."
SPHEREx has also revealed evidence that rocky debris is being vented by 3I/ATLAS out into space.
Scientists say the comet is ejecting large grains and chunks of material too massive to be pushed far away from the comet's nuclear by the Sun's energy.
SPHEREx's brief comet sojourn
SPHEREx normally busies itself with mapping the sky to help astronomers understand more about the Universe.
It launched in March 2025 with the core mission of revealing the origins of the Universe, the evolution of galaxies and whether or not life exists elsewhere in the Galaxy.
SPHEREx is producing all-sky maps of the Universe and can observe in 102 different colours, each one revealing space in different wavelengths of light.
"Our unique space telescope is gathering unprecedented data from across the universe," says Yoonsoo Bach, deputy study lead from the Korea Astronomy and Space Science Institute.
"But in this case, our galaxy delivered a piece of a faraway star system to us only a few months after launch, and SPHEREx was ready to observe it.
"Science is sometimes like that: You’re in the right place at the right time."
