The European Space Agency (ESA) is preparing for a unique opportunity to study the interstellar comet 3I/Atlas from what could be the best vantage point in the solar system.
Astronomers made the rare and extraordinary discovery of an interstellar object in our own solar system on July 1, 2025, sparking a scramble to study the mysterious visitor. The object has since been named comet 3I/ATLAS, where 3I stands for “third interstellar,” and designated C/2025 N1 (ATLAS).
As it turns out, it may be observations from Mars, not Earth, that give us our closest look at the comet. 3I/ATLAS will come as close as around 18.6 million miles (30 million kilometers) to Mars, while it will only come within 168 million miles (270 million km) of Earth. That means spacecraft orbiting Mars are in play.
Colin Frank Wilson, Project Scientist for ESA’s Mars orbiters, confirmed that the agency is preparing to attempt observations of the interstellar object 3I/ATLAS during its passage through the solar system.
“We can confirm that we are planning to observe 3I/Atlas around the time of its closest approach to Mars,” Wilson said. “This is predicted to occur on 3 October 2025. On this date, the object will still be approximately 30 million kilometres from Mars.”
ESA will employ both Mars Express and the ExoMars Trace Gas Orbiter (TGO) spacecraft to make observations.
“We will attempt to obtain images of the object using the High Resolution Stereo Camera (HRSC) onboard Mars Express, and also with the Colour and Stereo Surface Imaging System (CaSSIS) onboard TGO,” Wilson explained.
The comet will be too distant for a real close-up look. However, if 3I/ATLAS is bright enough, HRSC may be able to hint at whether it’s elongated, spherical or irregularly shaped. The first discovered interstellar interloper, 1I/’Oumuamua, was unusually elongated and more asteroidal, while 2I/Borisov was more like a typical comet. CaSSIS, meanwhile, could provide insights into 3I/ATLAS’ volatile activity and its composition.
“We will also attempt to measure the spectrum of the object, using the TGO’s NOMAD and MEx’s OMEGA and SPICAM spectrometers,” Wilson said.
These payloads could tease out evidence of molecular signatures such as water vapor or organics in 3I/ATLAS’ coma if it becomes active. “However, we do not have great…
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