British News Agency

ESA used observation data obtained from the ExoMars Trace Gas Orbiter (TGO), which orbits Mars, in an innovative way, improving the estimated position of the comet by a factor of ten.

In ESA’s statement it was said: “By using data from Mars for an unusual observation, we improved our understanding of the path of the interstellar comet 3I/ATLAS through our Solar System. Although 3I/ATLAS poses no threat, it is a valuable test case for planetary defense.”

The statement described determining the trajectory of an interstellar comet using a Mars orbiter’s data as “a challenging task”: “The CaSSIS instrument was designed to image the nearby Martian surface in high resolution. This time, however, the camera was pointed at the sky above Mars to capture the tiny 3I/ATLAS passing against a starry background.”

Astronomers in ESA’s Planetary Defence team had to account for the special position of the orbiter, as they are accustomed to determining the orbits of comets and asteroids.

ESA noted that orbital observations are typically carried out from fixed observatories on Earth or from space telescopes such as Hubble or the James Webb Space Telescope.

“This time, the ephemeris of 3I/ATLAS — and particularly its accuracy — depended on taking into account the exact position of ExoMars TGO in its fast orbit around Mars. This required joint efforts from multiple ESA teams and partners.”

“The data obtained for 3I/ATLAS represent the first officially accepted astrometric measurements made from a spacecraft orbiting another planet and submitted to the Minor Planet Center (MPC), which serves as the central database for asteroid and comet observations.”