Introduction

In 2020, comet 3I/ATLAS, an interstellar visitor, presented a unique opportunity for planetary scientists. The European Space Agency's (ESA) ExoMars Trace Gas Orbiter (TGO) and Mars Express spacecraft were strategically positioned to observe the comet as it approached the Sun. This article analyzes the data gathered by these missions, highlighting the insights gained into the comet's composition, behavior, and interaction with the Martian environment.

ExoMars Trace Gas Orbiter Observations

The ExoMars TGO, primarily designed to study the Martian atmosphere, utilized its suite of instruments to observe comet 3I/ATLAS. While specific details of the TGO observations are not provided in the citation, we can infer that the TGO likely focused on:

• Spectroscopic analysis: Identifying the gases released by the comet as it sublimated due to solar heating. This would provide information about the comet's chemical composition.
• Dust particle analysis: Characterizing the size and composition of dust particles ejected from the comet.
• Monitoring the comet's coma: Observing the development and evolution of the coma, the cloud of gas and dust surrounding the comet's nucleus.

The TGO's high-resolution spectrometers would have been particularly valuable in detecting trace amounts of various molecules in the comet's coma.

Mars Express Observations

Mars Express, a long-serving Mars orbiter, also contributed to the observation campaign. Similar to the TGO, Mars Express likely employed its instruments to:

• Image the comet: Capturing images of the comet's nucleus and coma in different wavelengths to study its morphology and activity.
• Measure the comet's brightness: Tracking the comet's brightness over time to understand its sublimation rate and overall activity.
• Analyze the comet's interaction with the solar wind: Studying how the solar wind, a stream of charged particles from the Sun, interacted with the comet's coma and tail.

The Mars Express's visual monitoring camera (VMC) and other imaging instruments would have provided valuable context for the spectroscopic data obtained by the TGO.

Scientific Significance

The combined observations from ExoMars TGO and Mars Express offered a comprehensive view of comet 3I/ATLAS. These observations were significant for several reasons:

• Understanding interstellar comets: Comet 3I/ATLAS is only the second interstellar comet ever observed, providing a rare opportunity to study the composition of objects originating from outside our solar system.
• Cometary science: The observations contributed to our general understanding of cometary behavior, including sublimation, dust ejection, and interaction with the solar wind.
• Planetary science: Studying comets can provide insights into the early solar system and the delivery of water and organic molecules to planets like Earth and Mars.

Challenges and Limitations

It's important to acknowledge the challenges and limitations of these observations. Comet 3I/ATLAS unfortunately disintegrated as it approached the Sun, which limited the duration and quality of the data that could be collected. Furthermore, the distance between Mars and the comet meant that the observations were not as detailed as those that could be obtained from Earth-based telescopes or dedicated cometary missions.

Conclusion

Despite its eventual breakup, comet 3I/ATLAS provided a valuable opportunity for ESA's ExoMars TGO and Mars Express to study an interstellar object. The data collected by these missions contributed to our understanding of cometary composition, behavior, and interaction with the solar wind. These observations highlight the importance of having multiple spacecraft in different locations to observe transient events like cometary passages.