The European Space Agency and NASA are coordinating multiple spacecraft, including missions at Mars and Jupiter, to study the interstellar comet 3I/ATLAS. These observations will provide a unique opportunity to analyze the object's composition as it makes its closest approach to the sun this year.
Discovered in July 2025, 3I/ATLAS is the third confirmed object from outside our solar system to be detected. Its high speed and trajectory confirm its interstellar origin, making it a target of significant scientific interest.
Key Takeaways
- Interstellar comet 3I/ATLAS is being tracked by multiple ESA and NASA spacecraft.
- Observations will occur as the comet becomes difficult to see from Earth.
- The primary goal is to analyze the comet's chemical composition during its closest approach to the sun.
- Data could reveal whether planetary systems share common building blocks or contain exotic materials.
A Visitor From Another Star System
Astronomers first identified 3I/ATLAS in July 2025 using the Asteroid Terrestrial-impact Last Alert System (ATLAS) telescope in Chile. The object's path through our solar system immediately distinguished it as an interstellar visitor.
Unlike comets native to our system, 3I/ATLAS does not follow a closed orbit around the sun. Instead, it is on a hyperbolic trajectory, meaning it will pass through once and then continue its journey into deep space.
High-Velocity Traveler
The comet is moving at an estimated speed of 130,000 mph (219,000 km/h). This extreme velocity is a key indicator that it is not gravitationally bound to our sun and originated from another star system.
While ground-based telescopes can track the comet until September 2025, its path will soon take it too close to the sun to be observed from Earth. This limited window makes space-based observations essential for a complete study.
Coordinated Spacecraft Observations
A fleet of planetary missions will provide a continuous watch on 3I/ATLAS as it disappears from Earth's view. These spacecraft are positioned in different parts of the inner solar system, offering unique vantage points.
Mars Orbiters Take First Look
According to the European Space Agency, its Mars missions will be the first to conduct detailed observations. "Between 1 and 7 October, our Mars orbiters Mars Express and ExoMars Trace Gas Orbiter will observe the comet as it passes close to Mars," ESA stated.
The closest distance between the Mars spacecraft and the comet is expected to be 30 million kilometers on October 3. Other orbiters at Mars, including NASA's Mars Reconnaissance Orbiter (MRO), are also in a position to gather data.
Multiple Missions Involved
The observation campaign involves a diverse set of spacecraft:
- ESA Mars Express: An orbiter studying Mars since 2003.
- ESA ExoMars Trace Gas Orbiter: Analyzing the Martian atmosphere.
- NASA Psyche: Currently en route to the metallic asteroid 16 Psyche.
- ESA Juice: A mission heading to study Jupiter's icy moons.
Juice Mission to Capture Peak Activity
ESA's Jupiter Icy Moons Explorer (Juice) will observe 3I/ATLAS between November 2 and 25. This timing is critical because it occurs just after the comet reaches perihelion—its closest point to the sun.
The intense solar radiation at perihelion will cause the comet to become highly active, providing the best opportunity for scientists to study its composition.
The Scientific Importance of Perihelion
The primary scientific objective is to understand what 3I/ATLAS is made of. The period around perihelion is the most crucial for this investigation.
As the comet nears the sun, its surface ices will heat up and vaporize, a process called sublimation. This activity releases gas and dust that were trapped within the comet's nucleus, forming a bright halo, or coma, and a long tail.
"JUICE will be in the best position for the important period around the 3I/ATLAS perihelion, when observations from Earth will be the hardest," said T. Marshall Eubanks, Chief Scientist at Space Initiatives Inc.
By analyzing the light from this released material, scientists can determine its chemical makeup. This provides a chemical fingerprint of the comet and, by extension, a sample of the material from its home star system.
Unlocking Secrets of Other Star Systems
The data gathered from 3I/ATLAS could answer fundamental questions about planetary formation across the galaxy. Scientists will compare its composition to that of comets originating from our own solar system's Oort Cloud and Kuiper Belt.
If the chemical makeup is similar, it would suggest that the building blocks for planets and comets are common throughout the galaxy. This would imply that systems similar to our own could be widespread.
However, if 3I/ATLAS contains different ratios of elements or exotic materials not typically seen in our comets, it would provide a fascinating glimpse into the unique chemistry of another stellar nursery. Either outcome will provide unprecedented insight into the nature of interstellar objects and their role in the galaxy.