NASA's fleet of solar-observing spacecraft were able to capture images of comet 3I/ATLAS as it passed behind the Sun, from our perspective on Earth.
The interstellar comet is travelling through our Solar System, having formed about 7 billion years ago around a distant star elsewhere in the Galaxy.
Time is of the essence, if astronomers are to learn as much as they can about 3I/ATLAS before it leaves our Solar System and disappears from view forever.
More on 3I/ATLAS
During October 2025, the comet passed behind the Sun, but has now, as of late November, reemerged into view from Earth.
While it was obscured by the Sun, NASA and the European Space Agency were able to point their Mars rovers and orbiters at the comet.
ESA's Trace Gas Orbiter, for example, captured images of 3I/ATLAS, and those observations have enabled scientists to recalculate the comet's trajectory to a much higher degree.
But as well as Mars spacecraft, a few solar-observing space missions were also able to observe 3I/ATLAS during its period behind the Sun.
NASA's solar missions have caught comets on camera before, but this was the first time its heliophysics missions had purposefully observed an object from another star system.
They were tasked with giving scientists more information about the comet's size, physical properties and chemical makeup.
This is what they saw.
STEREO-A
NASA’s STEREO (Solar Terrestrial Relations Observatory) was the first solar mission to begin observing comet 3I/ATLAS, and it did so from 11 September to 2 October 2025.
The STEREO mission is designed to study activity on the Sun, and how solar activity affects the planets of the Solar System.
Scientists thought 3I/ATLAS would be too faint for STEREO to see, but a clever imaging technique, known as stacking, saw multiple images overlaid to help bring out the minute details of the comet.
Using this technique, images captured by STEREO's Heliospheric Imager-1 instrument, which observes in visible light, were able to bring the comet into view.
Its view of 3I/ATLAS consists of black and pink streaks, with the comet visible as a hazy white blob at the centre.
PUNCH
NASA's PUNCH (Polarimeter to Unify the Corona and Heliosphere) spacecraft is primarily tasked with observing coronal mass ejections, which are powerful bursts of plasma erupting from the surface of the Sun.
And it's this ability to observe areas of the sky near the Sun that enabled PUNCH to track comet 3I/ATLAS as it passed close to our host star.
Images here, including an animation produced using multiple frames, show comet 3I/ATLAS from 28 September to 10 October 2025, when the comet was between 372 million to 378 million km (231 million to 235 million miles) from Earth.
Each of the frames in the animation is made up of multiple observations taken each day.
Because PUNCH was locked on tracking 3I/ATLAS across the sky, more distant stars appear as streaks of light in the background.
Similar streaks were seen, for example, in the Gemini South images of 3I/ATLAS and the Hubble Space Telescope images of 3I/ATLAS.
A few frames show a really bright object streaking past the comet. That's the planet Mars.
PUNCH's observations show 3I/ATLAS's tail, seen as a slight elongation to the lower right, around the 4 o'clock mark.
Because the comet was so faint during these observations, the PUNCH science team weren't sure the spacecraft would be able to see it clearly.
But stacking multiple images of the comet seems to have worked, bringing out the shape of 3I/ATLAS and its tail even against the bright glare from the Sun.
"We’re really pushing the limits of the system," says Kevin Walsh of the Southwest Research Institute in Boulder, Colorado, USA, who led PUNCH’s observations of the comet.
SOHO
The Solar and Heliospheric Observatory, or SOHO, is jointly operated by NASA and the European Space Agency.
It's the latest solar observer to view comet 3I/ATLAS, which it did between 15–26 October 2025.
SOHO is primarily tasked with observing the Sun, but has spotted quite a few comets in its time.
Since its launch in 1995, it's seen more comets than any other space mission.
In fact, as part of the NASA-funded Sungrazer Project, with the help of citizen scientists, SOHO images have led to the discovery of more than half of all known comets, according to NASA.
The spacecraft’s Large Angle and Spectrometric Coronagraph (LASCO) instrument suite saw 3I/ATLAS crossing its field of view from 358 million km (222 million miles) away.
That's over twice the distance between Earth and the Sun.
Again, 3I/ATLAS was expected to be too faint for SOHO to see, but image processing and stacking have brought the comet clearly into view.
The interstellar comet continues to amaze. If you'd like to try and see if for yourself, catch up with our blog on how to observe comet 3I/ATLAS.
