Martian Eyes on an Interstellar Wanderer: How ESA's Orbiters Tracked Comet 3I/Borisov

In a remarkable demonstration of scientific adaptability, two of the European Space Agency's (ESA) premier Mars orbiters – Mars Express and the ExoMars Trace Gas Orbiter (TGO) – momentarily pivoted from their primary mission of studying the Red Planet to become impromptu deep-space observatories.

Their target? Comet 3I/Borisov, the second-ever interstellar object detected and the very first interstellar comet, which offered humanity a fleeting glimpse of material from another star system.

Comet 3I/Borisov, a cosmic vagabond, made its closest approach to the Sun in December 2019, having journeyed from beyond our solar system.

Its interstellar origin made it an object of immense scientific curiosity, prompting astronomers worldwide to train their instruments on it. However, the unique vantage point offered by spacecraft orbiting Mars provided an unprecedented opportunity to study this alien visitor up close, yielding data that simply couldn't be obtained from Earth.

The challenge was formidable.

Observing a fast-moving, relatively dim comet from a Martian orbit required rapid planning and precise execution by mission control teams. Both Mars Express and TGO, designed primarily for studying Martian geology and atmosphere respectively, had to be carefully reoriented to point their instruments towards the distant comet.

This unexpected astronomical task showcased the incredible versatility and robust engineering of these missions.

Mars Express, a seasoned veteran in orbit since 2003, utilized its High Resolution Stereo Camera (HRSC) to capture detailed images of the comet's coma and tail. The HRSC, typically used for mapping Mars's surface in stunning detail, provided valuable insights into the immediate vicinity of Borisov's nucleus.

Additionally, the Visual Monitoring Camera (VMC), affectionately known as the 'Mars Webcam,' contributed by providing wide-field views, showcasing the comet's majestic tail stretching across the void.

The ExoMars Trace Gas Orbiter (TGO), a newer arrival at Mars, also joined the observational campaign.

Its Colour and Stereo Surface Imaging System (CaSSIS), renowned for its high-resolution color imaging capabilities of the Martian surface, was instrumental in capturing images that helped scientists analyze the composition of the comet's dust and gas. These multi-instrument observations from different spacecraft provided complementary data, allowing researchers to build a more comprehensive picture of Borisov's characteristics.

The observations revealed fascinating details about Comet 3I/Borisov's structure, its gas and dust production rates, and the dynamics of its coma and tail.

Understanding these properties is crucial because this comet represents primordial material from a different star system, offering clues about the formation processes beyond our own stellar neighborhood. Comparing its characteristics to comets originating within our solar system provides an invaluable benchmark for understanding planetary system evolution.

While Martian orbiters have previously observed comets passing near Mars, such as Comet C/2013 A1 (Siding Spring) in 2014, the interstellar origin of 3I/Borisov elevated these observations to a new level of scientific significance.

It underscored the remarkable capability of our robotic explorers to adapt and contribute to astronomical discovery far beyond their initial design parameters. As we continue to explore the cosmos, these adaptable missions remain our eyes and ears, ready to capture the unexpected wonders the universe has to offer.