In a stunning feat of interplanetary ingenuity, two probes orbiting the Red Planet have turned their gaze away from the dusty surface to capture a once-in-a-lifetime event: the passage of the mysterious interstellar comet 3I/ATLAS, an event virtually invisible from Earth.
Located several hundred million kilometers from home, Mars is currently the best seat in the solar system for a unique celestial spectacle. The visitor, known as 3I/ATLAS, is a comet from another star system, screaming through our cosmic neighborhood at a breathtaking speed of over 60 kilometers per second. But for astronomers on Earth, observing this rare guest has been a challenge due to its position in the sky.
Faced with this limitation, a team of resourceful scientists at the European Space Agency (ESA) devised an audacious plan. They repurposed two of their workhorse spacecraft at Mars—the veteran Mars Express and the newer ExoMars Trace Gas Orbiter (TGO)—to act as long-distance spies.
A Seemingly Impossible Task
The challenge was monumental, pushing the probes' instruments far beyond their original design. The cameras on these orbiters are engineering marvels, but they are optimized for studying the Martian surface and its atmosphere from distances of less than 1,000 kilometers. Comet 3I/ATLAS, by comparison, was a staggering 29 million kilometers away from the probes at the time of observation, appearing as an incredibly faint speck in the void.
"It was a 'Hail Mary' observation, to be honest," explained an ESA mission scientist, speaking on the incredible difficulty. "Not only was the comet astronomically far, but it was also about 10,000 times less bright than the objects these cameras are built to study. We were asking them to see a candle flame from the other side of a city."
The ExoMars TGO Rises to the Occasion
Despite the odds, the team pressed on, focusing their efforts on the state-of-the-art Colour and Stereo Surface Imaging System (CaSSIS) aboard the ExoMars Trace Gas Orbiter. After painstakingly pointing the orbiter and programming the camera, they waited for the data to stream back.
The result was nothing short of spectacular. Against all expectations, the CaSSIS instrument managed to lock onto the faint, speeding comet. The image it returned is a testament to human and technological perseverance. You can see the incredible, animated observation for yourself in this official GIF released by the ESA.
Watch the ExoMars Trace Gas Orbiter observe comet 3I/ATLAS in this official ESA GIF.
The details are breathtaking. The image clearly shows the comet's bright, condensed coma—the ghostly green glow of its atmosphere. This envelope of gas, primarily water vapor and dust, is being blasted off the comet's icy nucleus by the Sun's radiation, creating the characteristic halo that makes comets so mesmerizing.
More Than Just a Pretty Picture: The Science Behind the Sighting
This successful observation is far more than a photographic trophy. For scientists, it's a goldmine of data. By analyzing the composition and structure of the coma, researchers can begin to unravel the secrets of this interstellar traveler. What is it made of? How does its chemistry compare to comets native to our solar system?
The very nature of its origins—from another star system—has even led some in the astronomical community to whimsically refer to it as an "alien probe," highlighting its profound mystery. Every pixel in the TGO's image helps to replace science fiction with scientific fact.
This successful observation underscores the incredible versatility of missions like the ExoMars Trace Gas Orbiter, which, while designed to sniff out gases like methane in the Martian atmosphere, can be adapted for groundbreaking astrophysics. Similarly, the enduring Mars Express probe, which also participated in the campaign, continues to deliver valuable data decades after its arrival, proving the immense value of long-term orbital assets. You can learn more about its ongoing mission on the ESA's dedicated Mars Express page.
What's Next for the Interstellar Comet?
The story of 3I/ATLAS is far from over. In a perfect handoff of cosmic observation, ESA's JUpiter ICy moons Explorer (Juice) mission is poised to take over the watch. As the comet continues its journey and reaches its closest point to the Sun, or perihelion, Juice's powerful instruments will be perfectly positioned for an even closer look.
There is no doubt that the upcoming observations from the Juice mission will provide conclusive new data on the object's composition and trajectory, helping to pinpoint exactly which corner of the galaxy this mysterious visitor came from.
For now, thanks to the sharp eyes of two Martian orbiters, we have been given a secret glimpse of a passerby from the great interstellar dark—a fleeting reminder that our solar system is not an island, but a dynamic port in a vast, flowing cosmic sea.
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