Thanks to the data collected by the Colour and Stereo Surface Imaging System (CaSSIS) onboard ESA’s Trace Gas Orbiter (TGO) spacecraft orbiting Mars, scientists have improved the predicted location of the interstellar comet 3I/ATLAS by a factor of 10.
This image of the interstellar comet 3I/ATLAS was captured on October 3, 2025 by the CaSSIS instrument aboard ESA’s Trace Gas Orbiter. Image credit: ESA / TGO / CaSSIS.
3I/ATLAS was discovered by the NASA-funded ATLAS (Asteroid Terrestrial-impact Last Alert System) survey telescope in Rio Hurtado, Chile, on July 1, 2025.
Until September, figuring out the location and trajectory of the interstellar comet relied on Earth-based telescopes.
Between October 1 and 7, TGO turned its eyes towards 3I/ATLAS from its orbit around Mars.
The comet passed relatively close to Mars, approaching to about 29 million km during its closest phase on October 3.
The Mars probe got about 10 times closer to 3I/ATLAS than telescopes on Earth and it observed the comet from a new viewing angle.
The triangulation of the TGO/CaSSIS data with the data from Earth helped to make the comet’s predicted path much more accurate.
While the scientists initially anticipated a modest improvement, the result was an impressive 10-fold leap in accuracy.
“It was a challenge to use the Mars orbiter’s data to refine an interstellar comet’s path through space,” members of the TGO team said in a statement.
“The CaSSIS instrument was designed to point towards the nearby Martian surface and look at it in high resolution.”
“This time, the camera was aimed at the skies above Mars to catch the tiny, distant 3I/ATLAS sweeping by across a starry backdrop.”
Astronomers in the planetary defense team at ESA’s Near-Earth Object Coordination Centre, used to determining the trajectories of asteroids and comets, had to account for the spacecraft’s special location.
“Usually, trajectory observations are made from fixed observatories on Earth, and occasionally from a spacecraft in near-Earth orbit, like the NASA/ESA Hubble Space Telescope or the NASA/ESA/CSA James Webb Space Telescope,” the researchers said.
“The astronomers are well-practiced in considering their location as they determine the future locations of objects, called ephemeris.”
“This time, the ephemeris of 3I/ATLAS, and in particular the prediction’s precision, depended on accounting for the exact location of TGO: at Mars and in a fast orbit around it.”
“It required working together in a combined effort by several ESA teams and partners, from flight dynamics to science and instrument teams.”
Challenges and subtleties that are usually negligible, had to be tackled to reduce the margins as much as possible, in order to achieve the highest accuracy possible.”
![The image shows NGC 1866 superimposed with a false color image from the MUSE data cube, where the ionized shell of the planetary nebula Ka LMC 1 is seen as a red ring. The grayscale insets illustrate the different size of the ionized shells of singly ionized nitrogen [N II] and doubly ionized oxygen [O III]. The magnified Hubble image near the center of the ring reveals the presence of a pale blue star -- most probably the hot central star of Ka LMC 1. Image credit: AIP / M.M. Roth / NASA / ESA / Hubble.](https://cdn.sci.news/images/2025/11/image_14348-Ka-LMC-1-104x75.jpg)
